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Chemical Pathology > Chemical Pathology > Flashcards

Chemical Pathology Flashcards

1
Q

What is the chemical structure of porphyrin molecules?

A

It is a cyclic compound with 4 pyrrole rings connected by methenyl bridges.
The 4 nitrogen molecules at the centre can bind metal (iron) ions.

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2
Q

What are the symptoms of porphyria?

A

Skin lesions (exposure to light causes them to release free radicals = itching and rash) - not in AIP
Neurovisceral sx - ALA and PBG in excess

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3
Q

How are porphyria’s classified?

A

1) According to the organ the metabolites accumulate the most in.
O Erythtopoeitic = CEP and EPP
O Hepatic = AIP, HC, VL, PCT

2) acute/non-acute
O Acute = AIP, HC, VP
O Non-acute = PCT, CEP, EPP

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4
Q

What are the phases of acute porphyria and what do these said phases include?

A

Latent phase - enzyme defect
Acute phase - excessive ALA and PBG production

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5
Q

How do you treat an acute porphyria attack?

A

Supportive - fluids and electrolyte balance, IV haem arginate, pain relief, anti-emetics, adequate carb intake

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6
Q

What is an acute porphyria attack commonly mistaken for and why is this dangerous?

A

Acute abdomen, the pt will be taken to theatre and they will die

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7
Q

Which enzyme is deficient in Congenital erythropoietic porphyria?

A

Uroporphyrinogen III cosynthase

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8
Q

What are the clinical features of congenital erythropoeitic porphyria?

A

O Severe photosensitivity with scarring in infancy
O alopecia + hypertrichosis
O brownish/ pink teeth → red under uv light
O haemolytic anaemia

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9
Q

What tests do you request if you suspect congenital erythropoeitic porphyria and what results would you expect?

A

Urine: uro> copro I
Faeces: copro> proto
RBC’s: uro + copro

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10
Q

What enzyme is deficient in erythropoeitic protoporphyria?

A

Ferrochelatase

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11
Q

How does erythropoeitic protoporphyria present?

A

O mild anaemia
O porphrin gallstones
O liver cirrhosis and liver failure
O skin lesions (milder than CEP)

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12
Q

What tests would you request for EPP and what results would you expect?

A

Faeces: proto > copro
RBC’s: proto

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13
Q

What enzyme is deficient in Porphyria cutania tarda?

A

Uroporphrinogen decarboxylase

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14
Q

What are the clinical features of porphyria cutania tarda?

A

Oskin lesions only
O hypertrichosis
Ohyperpigmentation

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15
Q

What may provoke sx in PCT?

A

Ooestrogens
Oalcohol abuse
O Iron overload

(They learn to avoid these)

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16
Q

What would you test for in suspected pct?

A

Urine: uro>copro
Fecal: isocopro

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17
Q

What are some clinical features of an acute porphyria attack?

A

O git: abode pain, constipation, vomiting
O CVS: ↑ HR, hypertension
O CNS: convulsions, depression, psychosis
O peripheral neuropathy: pain, stiffness, weakness, numbness, pins + needles

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18
Q

Predisposing factors of porphyria acute attack

A

O anaesthesia
O alcohol
O oestrogens
O premenstrual
O carbamazepines
O sulphonamides
O stress / infection

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19
Q

What enzyme is deficient in acute intermittent porphyria?

A

PBG deaminase

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20
Q

Symptoms of AIP

A

Mostly asymptomatic
Neurovisceral sx in acute attack

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21
Q

What tests would you request in suspected AIP and expected? Results

A

Latent phase: ALA<PBG
Acute phase: ALA<PBG, uro from PBG

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22
Q

What enzyme is deficient in varigate porphyria?

A

Protoporphrinogen oxidase

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23
Q

What clinical sx of VP?

A

Latent phase: Asymptomatic / skin lesions
Acute phase: Neurovisceral sx

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24
Q

What tests would you order for VP?

A

O urine:
> acute - ALA, BPG, copro> uro
Ofaecal:
> acute- proto> copro
> latent -proto> copro

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25
Q

What enzyme is deficient in hereditary coproporphyria?

A

Coproporphyrinogen oxidase

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26
Q

What is the clinical presentation of hereditary coproporphyria?

A

OLatent phase: rarely skin lesions
OAcute phase: neurovisceral sx

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27
Q

What tests would you order and what results would you expect in hereditary coproporphyria?

A

O urine:
> acute - ALA, PBG, copro > uro
O fecal:
> latent- copro> proto
> active - copro> proto

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28
Q

What is the cause of 2° porphyria?

A

When its not due to an enzyme deficiency but something else causing excess porphrin production
O lead toxicity - inhibits ALA dehydrates, ferochelatase, coproporphrinogen oxidase
O liver disease
O chronic kidney failure
O bleeding stomach/ duodenum
O toxin exposure

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29
Q

What is the minimum volume of water that needs to be excreted by the kidneys for adequate waste removal?

A

500ml/24hrs

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30
Q

What is the physiological response to water loss?

A

O vasopressin release = water retention by kidneys
O hypothalamic thirst centre stimulated
O water ICF →ECF down conc. Gradient

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31
Q

What systems are responsible for sodium and water homeostasis?

A

RAAS
ADH/Vasopressin

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32
Q

How is water and sodium regulated?

A

①↓ effective blood volume
>↓ CO
> systemic vasodilation (sepsis)
>↓ECF (blood loss)
② vasopressin released → kind absorb water
③↑ sympathetic NS
> systemic vasoconstriction →↑BP
> arterial vasoconstriction →↓GFR =↑ water retained = blood volume
④RAAS activation = ↑ sodium + water retention

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33
Q

What causes pseudohyponatraemia?

A

Excess lipids/proteins

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34
Q

What is important to remember when correcting hyponatraemia?

A

Acute = emergency → treat rapidly (MEDICAL EMERGENCY)
Chronic = increase the sodium slowly as the body has adapted to this level

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35
Q

What are complications of acute hyponatraemia?

A

Cerebral oedema ( water goes intracellularly as ↓ extracellular sodium )
> N & V
> confusion
> coma
> death

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36
Q

How do you diagnose syndrome of inappropriate ADH?

A

Diagnostic criteria: (exclude other causes of hyponatraemia )
o hyponatraemia and low serum osmolality
o normal ECF volume
o urine not excessively diluted ( osmolality>100 )
o normal kidney, adrenal, thyroid fxn
o pt not on any drug that may cause hyponatraemia

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37
Q

What investigations needed in hyponatraemia?

A

O blood
> glucose
> lipids
> total protein
> potassium
> osmolality
> urea + creatinine
> TSH + T4
> haematocrit
O urine
> sodium
> osmolality

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38
Q

What are the causes of hyponatraemia?

A

O hyperglycaemia
O too much iv fluids
O congestive heart failure
Ocarcinoma of bronchus
Odiuretic therapy

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39
Q

When is hypernatraemia unlikely to occur?

A

O pts with access to water
O ability to drink
O intact thirst mechanism
O alert

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40
Q

How does the brain adapt to high/ low levels of sodium?

A

Hypernatraemia:
O brain produces idiogenic osmolytic molecules intracellularly to prevent water moving extracellularly

Hyponatraemia
O brain secretes idiogenic molecules to extracellular space to prevent watermoving intracellularly = cerebral oedema

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41
Q

What are some causes of hypokalaemia?

A

① intracellular shift ( alkalosis, insulin admin, refeeding syndrome,↑ k excretion )
② renal causes ( diuretics, AKI, tubular disorders )
③ extravenal ( diarrhoea, vomiting )
④↓ intake

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42
Q

What causes hyperkalaemia?

A

①spurious
> haemolysis
> EDTA contamination
> old sample
② transcellular movement
> acidosis
> tissue damage
>rhabdomyelitis
> k-sparing diuretics
>AKI +CKD
> mineral corticoid deficiency
③ excessive intake
> slow k
> parental infusion

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43
Q

What are some functions of calcium?

A

Obone + teeth structure
O2nd messenger system
O neuromuscular junction - Release neurotransmitters
O muscle contractions
O cofactor in coagulation factors

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44
Q

How do you calculate adjusted calcium?

A

① if [ alb ] < 40: [ca] + 0,02 X ( 40 - [alb] )
② if [alb] > 45: [ Ca] - 0,02 X( [ alb]- 45 )

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45
Q

What are the indications for measuring ionized calcium?

A

O hypercalcaemia of malignancy
O severe pancreatitis
O chronic kidney disease + dialysis
O transplantation
O massive transfusion
O extracorporeal transfusion
O critical illness
O hyperparathyroidism
O post-op parathyroïdectomy

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46
Q

What do you have to keep in mind when taking blood for ionized calcium measurement?

A

①stasis free blood taking method, fill tube maximally
② to the lab in 30mins so that centrifugation can occur within 1 hr
③ avoid removing test tube cap ( co2 into tube ↑ acidity = change ionized calcium levels )
④ keep sample on ice

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47
Q

What hormones regulate calcium homeostasis?

A

O PTH
O calcitonin
O vitamin D

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48
Q

What are the affects ofPTH On its target organs?

A

①bone
> ↑ osteoclast activity =↑ [Ca] plasma
> rapid release calcium
② kidneys
> ↑ calcium reabsorption
>↓ phosphate reabsorption
>↓ bicarb reabsorption = acidosis

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49
Q

What are the effects of calcitonin?

A

O inhibits osteoclast activity:↓ calcium reabsorption

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50
Q

What is fibroblast growth factor 23 (fgf 23 ) and what does it do?

A

It is a phosphotonin. it is secreted by osteoclasts when there is a ↑ phosphate + calcitriol and causes the kidneys to excrete more phosphate = phosphaturia. ( inhibits cotransporter )
= ↓ serum calcitriol and phosphate

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51
Q

Causes of hypercalcaemia

A

OPrimary hyperparathyroidism
O malignancy

O sarcoidosis
O Tb
O thyrotoxicosis
O persistent hyperparathyroidism after rents transplant
O vitamin D toxicity

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52
Q

What are the clinical features of hypercalcaemia

A

O git
>N&V
> abdominal pain
> constipation
> pancreatitis
O CVS
> ECG changes (↓ qt interval,↑ Pr interval)
> arrhythmias
O neuropsychiatric
> confusion
> lethargy, depression
> hypotonia, hyporeflexia, muscle weakness
O renal
> polyuria, polydipsia
> Kidney stones
>↓ GFR

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53
Q

Causes of hyperphosphataemia

A

O vit D intoxication
O chronic kidney injury + renal insufficiency
O hypoparathyroidism
O excess intake
O catabolic States eg: tumor lysis syndrome

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54
Q

What are complications of hyperphosphataemia?

A

O inhibits 1 alpha hydroxylation of 1,25 OH D in the kidneys
O phosphate may combine with calcium (opposite charges) → metastatic calcium deposits in tissues + hypocalcaemia

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55
Q

Management of hyperphosphataemia?

A

Treat the underlying cause
Phosphate binders

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56
Q

What are the causes of hypophosphataemia?

A

O↓ absorption ( malabsorption, vomiting, phosphate binding agents )
O redistribution ( DKA , resp alkalosis, enteral feed with inadequate phosphate )
O ↓ excretion via kidneys ( hyperparathyroidism)

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57
Q

Clinical effects of hypophosphataemia?

A

O mild sx
O it severe - muscle weakness (ATP is phosphate dependent)
O chronic hypophosphataemia = rickets, osteomalacia

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58
Q

Presentation of hypomagnesaemia?

A

O muscle weakness
O arrhythmias
O tetany
O ataxia
O delirium
O convulsions
O agitation

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59
Q

Causes of hypomagnesaemia?

A

O PPI’s
O diuretics
O malabsorption
O refeeding syndrome
O cirrhosis
O alcoholism
O drug toxicity

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60
Q

What are the dangers of hypermagnesaemia

A

O > 7,5 mmol/dl, can cause resp paralysis + cardiac arrest

On the other hand, can be useful to prevent bronchospasm in ICU pts ( btw 3-4 mmol/dl )

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61
Q

What causes secondary hyperparathyroidism?

A

O kidney injury
O vitamin D deficiency

=↓ synthesis calcitriol =↓ serum calcium = ↑ PTH

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62
Q

What ph does the stomach need to be for pepsinogen activation

A

Ph=3

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63
Q

What are the cells in the stomach and what do they secrete?

A

O parietal cells - HCl + intrinsic factor
O G-cells - gastric
O chief cells - pepsinogin
O d-cells - somatostatin

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64
Q

Vasoactive intestinal polypeptide - where is it secreted and what does it do?

A

O Regulates GI motility and secretions

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65
Q

Motion - where is it secreted and what does it do?

A

In the GI - stimulates motility

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66
Q

Gastric inhibitory peptide _ where is it secreted and what does it do?

A

O In the duodenum + jejunum - stimulates insulin release in response to ↑ glucose

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67
Q

Pancreatic polypeptide location + fxn

A

O released by the pancreas to inhibit exocrine fxn

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68
Q

Secretin location+ fxn

A

Duodenum + jejunum - stimulates pancreatic bicarb secretion

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69
Q

Define diarrhoea

A

Loose stool passage > 3 times per day

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70
Q

Differentiate chronic vs acute diarrhoea

A

Acute = <2 weeks (does not need to be investigated further )
Chronic = > 4 weeks

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71
Q

Classify diarrhoea

A

O small bowel - malabsorption, enzyme deficiency, crohns disease, bile salt malabsorption
O large bowel - crohns, ulcerative colitis
O pancreas - chronic pancreatitis, carcinoma, cystic fibrosis
O endocrine - gastronoma, carcinoid tumor
O other - laxatives, drugs,

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72
Q

What tests would you order to investigate chronic diarrhoea?

A

O FBC,U&E,LFT,ESR
O Ca, mg, na, K, PO4, albumin, folate, vitb12, iron
O fecal occult blood, fecal mc+s, fecal elastase, fecal calprotectin,

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73
Q

How do you further categorize chronic diarrhoea?

A

①secretary
> infection
> endocrine ( TSH, gastrin,
②osmotic
> lactose intolerance (hydrogen breath test)
> mg, carbs

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74
Q

How do you determine if its secretory or osmotic chronic diarrhoea?

A

① Osmotic gap of stools:
290 -2( [Na] + [k] )

> 125 = osmotic
< 50 = secretory

② Fecal ph < 5.6 = carb malabsorption

③ fecal laxative screening
Mg+phenyolphthalene

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75
Q

How is H. Pylori diagnosed?

A

Urea breathe test ( C14 labeled urea taken orally)
Stool antigen test

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76
Q

What is zollinger - Ellison syndrome

A

There is a gastrin producing tumor = ↑ acid secretion

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77
Q

How do you diagnose zollinger Ellison syndrome?

A

basal acid output (BAO)
= ng tube used to measure acid production over hr →> 15mmol/hr

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78
Q

What is coeliac disease?

A

Sensitivity to gliadin in all glutens = inflammation of small intestine → malabsorption

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79
Q

How do you diagnose coeliac disease?

A

O serology
> IgA EMA
> IgA tTG
O confirm with 3 duodenal biopsies
> HLA DQ2 / DQ8 in > 99% coeliac pts

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80
Q

What is fecal calprotectin?

A

O It is a protein found in the cytosol of leukocytes
O not digested by bower enzymes: ↑ amounts in faeces when inflammation
O used to differentiate irritable bowel syndrome to inflammatory bowel disease → avoid unnecessary colonoscopy

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81
Q

What is alpha 1 antitrypsin and why is it important?

A

It is a small protein that can be found in stool in protein loosing enteropathy because it is resistant to gut bacteria: not broken down

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82
Q

Causes of hypercalcaemia?

A

Malignancy
Hyperparathyroidism

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83
Q

Causes of hypercalcaemia?

A

Malignant disease
① widespread skeletal metastasis
② homeostatic malignancy
③ num eral hypercalcaemia of malignancy

Primary hyperparathyroidism
① sporadic
②familial

Less common
① vit D toxicity

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84
Q

Common drugs needing assessment for toxicology

A

Paracetamol
Lead
Iron
Ethanol
Salicylates (aspirin)

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85
Q

When do you take your sample for therapeutic monitoring?

A

When the drug is at a steady state (after about 5 half-lives)

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86
Q

Drugs with narrow therapeutic index

A

Phenytoin
Warfarin
Digoxin
Lithium

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87
Q

Phenytoin signs of toxicity and mechanism

A

Seizures - zero order kinetics cause phenytoin receptors to become saturated at therapeutic range therefore accumulates after that as can’t be eliminated

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88
Q

How does digoxin act and what is it used for

A

Inhibits Na/K ATPase pump
To treat a fib

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89
Q

Therapeutic range of digoxin

A

0,5-2 microgram/L for AF

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90
Q

Signs of digoxin toxicity

A

N&V
Dysrhythmias

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91
Q

Treatment of digoxin toxicity

A

Anti-digoxin antibodies

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92
Q

Another name for paracetamol

A

Acetaminophen

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93
Q

What metabolises paracetamol

A

Glucurodination and sulphation

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94
Q

Signs and sx of paracetamol poisoning

A

<24hr = nausea, vomiting, anorexia
24-48hr = abdo pain, ↑INR,
>48hr = jaundice, encephalopathy, AKI

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95
Q

What is the best marker of paracetamol poisoning severity

A

Prothrombin time

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96
Q

Treatment of paracetamol poisoning

A

① drug screen, liver + renal fxn
② N acetalcysteine ASAP
③ activated charcoal within 1hr of ingestion
④ 5% dextrose ( risk hypoglycaemia due to liver damage)

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97
Q

Signs of salicylate toxicity

A

①tinnitus
② resp alkalosis
③ then metabolic acidosis + N&V and electrolyte disturbances

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98
Q

Treatment of salicylate toxicity

A

Alkali is action of blood so that salicylate can ionise and be excreted in the urine.
NaHCO3, hydration, avoid hypoglycaemia, urine pH mustn’t exceed 8

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99
Q

Signs of iron toxicity

A

Circulatory collapse
encephalopathy
Renal failure
Liver necrosis

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100
Q

Treatment of iron toxicity

A

Desferroxamine
Fluids
Avoid hypoglycaemia

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101
Q

Lead toxicity blood levels that sx start

A

> 0,5

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102
Q

Sx of lead toxicity

A

Abdominal pain
N&V
Encephalopathy
Convulsions
Coma

Interferes with porphrin pathway

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103
Q

Lead toxicity tests

A

Urine - coporporphyrinogen III
Urine Aminolaevulinic acid

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104
Q

Treatment of lead toxicity

A

Chelation therapy (DMSA)

105
Q

What electrolyte changed occur in insulin deprivation?

A

Hyperkalaemia
Hyperphosphataemia

(Insulin cellular uptake of these)

106
Q

Electrolyte changes in insulin therapy?

A

Hypokalaemia
Hypophosphataemia
Hypomagnesaemia

107
Q

Pathophysiology of T2 DM

A

Increased lipolysis
Increased gluconeogenesis
Decreased in retain
Increased resorption of glucose in the kidneys
Decreased insulin production
Insulin resistance
Increased glucagonp

108
Q

Normal fasting glucose

A

<6.1

109
Q

2-hr glucose tolerance test

A

Fast overnight
75g glucose in 200ml water
Measure glucose before and after 2hrs
>11,1 = DM

110
Q

DM HbA1C

A

> 6.5% or >48mmol/L

111
Q

When can you NOT use HbA1C

A

New onset DM
Rapidly changing glucose levels
Sever Anaemia (low Hb <6.5)
Abnormal RBC lifespan
No HbA
Pregnancy

112
Q

How do you diagnose GDM

A

Oral glucose tolerance test >7.8

113
Q

What is the DKA triad

A

Hyperglycaemia
Ketones
Acidotic

114
Q

Biochemical abnorms in DKA

A

Hyperglycaemia
Hyperkalaemia
Hyponatraemia
Hyperphosphataemia
Metabolic Acidosis
Dehydration
Kidney injury

115
Q

How do you treat DKA?

A

IV saline
Insulin
Vit K, phosphate and magnesium

Check U&E and blood glucose every 6hrs
Monitor fluid status with CVP

116
Q

What is hyperosmolar hyperglycaemic state and treatment

A

No ketones, high blood glucose
DM2
Minimal acidosis

Treatment = fluids +low dose insulin

117
Q

Whipples tried

A

Hypoglycaemic sx
Hypoglycaemia
Sx resolve after glucose load

118
Q

Causes of fasting hypoglycaemia

A

Chronic kidney disease
Chronic liver disease
Cancer
Endocrine disease
Alcohol/drugs
Hyperinsulinaemia

119
Q

What is the expected pCO2 formula for METABOLIC ACIDOSIS?

A

Expected pCO2 = 1,5 x [HCO3] + 8
(range +/-2)

120
Q

What is serum protein electrophoresis used for?

A

It shows the levels of various proteins in the blood (albumin, alpha 1+2, beta and gamma)

Can help diagnose varies pathologies ie myeloma = spike in gamma

121
Q

What is serum immunofixation?

A

Helps identify which of the proteins from gel electrophoresis have spiked within the protein section

122
Q

What does hypoalbuminaemia indicate

A

CHRONIC liver disease, liver cirrhosis

123
Q

What is the serum ascites albumin gradient calculation and how does it help?

A

Serum albumin - ascites albumin (indicates if exudate/transudate)

124
Q

What does a high gradient SAAG indicate?

A

> 1,1
Portal HT, non-peritoneal cause of ascites, malnutrition, liver cirrhosis

<1,1
Peritoneal cause of ascites eg cancer, TB

125
Q

Which cofactors in the clotting cascade are dependent on Vit K

A

2, 7,9,10

126
Q

What markers of liver disease guide you towards alcohol induced

A

AST:ALT >2
Gamma GT increased
Increased triglycerides
Increased serum IgA
Red cell macrocytosis

127
Q

What type of bilirubin causes bilirubinuria?

A

Conjugated

128
Q

Lab findings in haemolytic jaundice?

A

Urine urobilinogen
Increased AST and LDH
Increased reticulocytes
Increased unconjugated bilirubin
Positive Coombs test

129
Q

What is delta bilirubin?

A

Conjugated bilirubin bound to albumin elevated in pts with long-standing obstructive jaundice/hyperbilirubinaemia

130
Q

Sources of ALP (explained isolated increase)

A

GIT
LIVER
BONE
PLACENTA
TUMORS

131
Q

Why does liver cirrhosis cause increased ammonia?

A

Liver converts ammonia to urea for excretion by kidneys therefore urea cycle affected by liver disease
Can lead to hepatic encephalopathy

132
Q

Formula for expected CO2 at compensated metabolic alkalosis

A

0,7 x [HCO3] +20 (+-5)

133
Q

AG formula

A

[Na] + [K] - [Cl-] - [HCO3]

134
Q

Causes of metabolic acidosis

A

DKA
Lactic acidosis
Kidneys unable to resort HCO3
Kidneys unable to excrete H+
Ingestion alcohol/salicylates

135
Q

Causes of metabolic alkalosis

A

Potassium depletion
Volume depletion (pyloric stenosis, gastric aspiration)
Chronic alkali intake

136
Q

Causes of respiratory acidosis

A

Airway obstruction
Depression of resp centre (anaesthesia, cerebral trauma)
Neuromuscular disease (Guillian Barre)
Pulmonary disease (severe pneumonia, pulmonary fibrosis)

137
Q

Causes of respiratory alkalosis

A

Increased respiratory drive (high altitude, severe anaemia)
Voluntary hyperventilation
Mechanical overventilation

138
Q

What is the normal amount of protein excreted in the urine?

A

Less than 150mg/24hrs

139
Q

What are the categories of proteinurea?

A

Persistent(1+ or more) = CKD

> 300mg/day (corrected for creatinine)

Benign

140
Q

Why do we test microalbuminurea and why does it help us?

A

Detects albumin at very low concentrations (more sensitive than dipstix)
Measures from 30-300mg/day
Indicates early nephropathy

141
Q

What are the mechanisms of proteinurea?

A

Secretory (kidneys or urinary tract secrete proteins)
Overflow (excess protein, kidney can’t resorb all)
Glomerular (permeability increased)
Tubular (impaired/saturated absorption)

142
Q

What is urine protein electrophoresis and how does it help us?

A

It’s used to determine what category of proteinurea we are dealing with.

143
Q

Causes of increased creatinine

A

Rhabdomyolysis
AKI
Diet
Patient stature
Drugs
Analytical interference

144
Q

Causes of low plasma creatinine

A

Elderly and infants
Chronic illness
Analytical interference
Vegetarians

145
Q

What is the formula for creatinine clearance?

A

[Urine creatinine] x (urine flow rate) / plasma creatinine concentration = ml/min

146
Q

GFR Formula

A

eGFR = 175 x [sCr x 0,011312]^-1,154 x age^-0,203

147
Q

When can eGFR be misleading?

A

> AKI
pregnancy
increased volume of distribution eg oedema of heart failure
malnutrition
extreme of age
meat fish meal
decreased or increased muscle mass

148
Q

What has been found more useful that creatinine in estimating kidney function?

A

Cystatin C

149
Q

Why is Cystatin C better than eGFR?

A

Not influenced by mass or sex
Single reference range for men and female under 50
Improved accuracy

BUT influenced by malignancy, hyperthyroidism and steroid tx

150
Q

Explain the exogenous pathway of fat metabolism

A

Enterocyte absorbs fat with apo B48. The chylomicron is then transported via lymph, through thoracic duct into circulation. It gains apo E, C1,2 and 3 from HDL. Hydrolysis of the chylomicron allows fatty acids to be released and absorbed by fat and muscle tissue. Glycerol to the liver. Now the chylomicron is dense cholesterol. Apo C’s are given back to HDL. This is removed from circulation by the liver.

151
Q

Explain the endogenous pathway of fat metabolism

A

The liver releases VLDL with only apo-100. It gains C1-3 and E app’s from HDL. The triglyceride is hydrolysed by LPL and fatty acids are released and taken up by fat and muscle. The VLDL reduces in size (IDL now). Some of the IDL is removed by receptor mediated pathways and it is now LDL (by hepatic lipase). The uptake of LDL is dependent on LDL receptors.

152
Q

Function of HDL

A

The precursor for HDL (nascent HDL) is released by the liver with Apo A1+2 apo, apo E and phospholipids. It is disc shaped. These molecules absorb free cholesterol to become HDL3. hDL3 is esterified by LCaT which allows it to have more carrying capacity for cholesterol. The cholesterol esters move to the centre and it becomes spherical.

HDL3 accepts apo C2+3 and phospholipids from cholesterol and VLDL and then at HDL2.
The cholesterol in HDL2 is exchanged with chylomicron and VLDL for triglycerides. (Mediated by CETP)
VLDL now with cholesterol esters is removed by the liver.

153
Q

Classify dyslipidaemias

A

Primary
Secondary (exclude first)

154
Q

Describe the pathophysiology of familiar hypercholesterolaemia

A

There is a mutation in the gene coding for the LDL receptors. (Apo B100) It is a dominant gene. 1 mutation = receptors working @ 50%. 2 mutations = 0 receptors working.

Heterozygous = 7.5-12mmol/L total (>4.5 LDL)
Homozygous = up to 20mmol/L

155
Q

What does familial dysbetalipoproteinaemia present with typically?

A

Fat deposits in palmar crease and tuberous xanthomata.
Excess IDL and chylomicron remnants which can’t be cleared

156
Q

List Causes of secondary dyslipidaemias NB

A

Diabetes
Obesity
Excess alcohol intake
Hypothyroidism
Nephrotic syndrome
Cholestasis
Chronic renal failure
Drugs

157
Q

What is the Framingham risk score used for?
What does it consist of? NB

A

Used to determine LDL treatment target
Defines the risk of suffering CV event in the next 10y without treatment.

Low risk <3%
Mod 3-15%
High 15-30%
Very high >30%

Includes gender, age, systolic BL, TG, HDL, smoker status

158
Q

When do you NOT use the Framingham risk score?

A

If the patient has already suffered a CV event
OR
Strong family history of CV event
→ treat

159
Q

Who qualifies for a lipogram?

A

anyone above 40y old

160
Q

What is the formula to calculate LDL?

A

Total cholesterol - (HDL + TG/2.2)

Invalid if TG >4.5

161
Q

Why do we treat hyperlipidaemia?

A

Decrease risk CV event and pancreatitis

162
Q

What are paraneoplastic endocrine syndromes?

A

When hormones or hum oral factors are secreted by the tumor

163
Q

What are the most common paraneoplastic endocrine syndromes.

A

Cushing Syndrome
Syndrome of inappropriate ADH
Hypercalcaemia of malignancy

164
Q

What are the effects of ectopic vasopressin secretion?

A

Dilutional hyponatraemia
With water retention
(SIADH)

165
Q

What are the sx of hyponatraemia?

A

Asymptomatic
Drowsiness
Confusion
Fits
Coma

166
Q

Which tumors increase ADH concentration

A

Small cell Ca of bronchus
Carcinoid tumors
Breast cancers
Pancreatic adenocarcinomas

167
Q

What is the pathophysiology of hypercalcaemia in malignancy?

A

PTH secreting peptides are released bY the tumor which stimulates the kidney to reabsorb more calcium (the PTH peptides from the tumor are not regulated)

Some tumors have osteoclast activating cytokines (myeloma)
And prostaglandins produced by metastasis (breast Ca)

168
Q

How do malignant diseases harm the kidneys?

A

Hypercalcaemia, cytotoxic drugs, urinary tract obstruction, antibiotics, Bence Jones proteinurea, kidney infiltration, tumor lysis syndrome (TLS)

169
Q

What is tumor lysis syndrome?

A

Cytotoxic drugs break down tumors causing massive tumor necrosis and
Hyperkalaemia
Hyperphosphataemia
Hyperuricaemia
Hypocalcaemia

170
Q

How do you prevent tumor lysis syndrome?

A

Fluids, allopurinol to inhibit Uris acid synthesis, careful fluid and electrolyte monitoring

171
Q

Where do gastroenteropancreatic neuroendocrine tumors arise from?

A

Neuroendocrine cells derived from the embryological gut

172
Q

What is carcinoid syndrome?

A

When vasoactive amines such as serotonin and peptides such as ACTH are secreted into circulation from a tumor.

173
Q

Another name for serotonin

A

5 hydroxytryptamine (5 HT)

174
Q

Symptoms of carcinoid syndrome

A

Pellagra like skin lesions (decreased nicotinic acid production - it’s diverted to make serotonin)
GI - N&V, diarrhoea, colicky pain
CVS - flushing, pulm stenosis
Resp - bronchospasm

175
Q

How do you screen for carcinoid syndrome?

A

24hr urine 5-hydroxyindk,eacetic acid (5-HIAA) = metabolite of serotonin

Chrimogranin A (less specific)

176
Q

What is an ideal tumor marker?

A

One that can be used for
Screening
Diagnosis
Prognosis
Treatment monitoring
Recurrence detection

177
Q

What is used to screen for Down syndrome?

A

Alpha fetoprotein (produced by yolk sac and embryonic liver and gut)

178
Q

What tumors does raised alpha fetoprotein indicate?

A

Hepatocellular Ca (but not specific)
Testicular germ cell tumors

179
Q

What tumor marker suggests colorectal cancer?

A

CEA (carcinoembryonic antigen)
Not sensitive or specific

180
Q

What may elevated hcg indication? (Extremely sensitive)

A

Choriocarcinoma (malignant prolif of hydatidiform mole)

181
Q

Classify acute coronary syndrome using tropoin and ECG

A

Unstable angina = normal troponin and nonspecific ECG
Non ST elevation MI = increased troop in and ST depression
ST elevation MI = increased troponin and ST elevation

182
Q

Pathogenesis of atherosclerosis

A

LDL trapped in subintimal space. Oxidises and attracts monocytes and macrophages to become foam cells.
Foam cells:
>secrete pro-inflam cytokines which attract leukocytes and cause endothelial damage
>secrete enzymes that erode plaque cap and increase risk of plaque rupture
>activate Th1 cells to products inflammatory cytokines

183
Q

Pathogenesis of Acute MI

A

Plaque of artherosclerosis ruptures, platelets aggregate and thrombosis is stimulates by Tissue Factor
Vascular occlusion by clot with/without embolisation plus vascular spasm which restricts blood flow

184
Q

What is STEMI

A

Abrupt total occlusion of major coronary artery causing transmural ischaemia/necrosis

185
Q

Treatment of STEMI NB

A

<12 hrs after event = percutaneous coronary intervention (PCI)with stent placement

If >120min delay expected = start fibrinolytic treatment and transfer to PCI capable hospital

186
Q

What is NSTEMI

A

Partial occlusion of major artery or total occlusion of minor artery causing partial thickness/subendocardial necrosis

187
Q

What troponin subunits are specific to myocardium

A

Troponin I and T

188
Q

How do you diagnose MI

A

1) test troponin (rise within 1-2hrs of onset)
2) use only highly sensitive troponin assay
3) repeat troponin over several hours to aid injury mechanism (occlusive or non-occlusive)
If first trop is normal but pt still unwell, might be an evolving AMI or unstable angina
4) repeat in 1-3hrs: >50% = diagnostic
5) NB FOR TEST: High and very high risk Framingham risk pts = involve cardiology

189
Q

Pitfalls of troponin

A

> causes rise and falls in coronary occlusion on serial testing
can’t distinguish between injury mechanisms (occlusion, inflam, toxic)
decreased clearance in kidne6 failure (monitor trends if creat>200)

190
Q

Point of care testing of trop pitfalls

A

Not highly sensitive
: will miss cases (but better than nothing in rural setting)

191
Q

Layers of the adrenal gland from outside in

A

Capsule
Zona glomerulosa
Zona fasciculata
Zona reticular is
Medulla

192
Q

What is the diurnal rhythm?

A

It shows how cortisol levels in the blood differ at different times of the day physiologically.

Lowest = midnight
Highest = 8am

193
Q

Causes of increased glucocorticoid

A

ACTH dependent
>pituitary (Cushing)
>ectopic
>ACTH therapy

ACTH independent
>adrenal adenoma
>adrenal carcinoma
>glucocorticoid therapy (steroid to)
>micronodular hyperplasia

194
Q

How do you test for Cushing Syndrome?

A

> Low-dose dexamethasone suppression test
urinary free cortisol
late night salivary cortisol

195
Q

Other tests when increased ACTH to determine origin

A

> potassium - hypokalaemic alkalosis (ectopic ACTH production due to increased output of mineralcorticoids)
selective venous sampling
pituitary function tests (to see if other hormones from the pituitary are affected = tumor?)
tumor markers
Glucose tolerance test (steroid induced diabetes)

196
Q

What is Cushing disease?

A

An increase in serum cortisol levels leading to sx related to this

197
Q

Causes of adrenal insufficiency?

A

① Primary (inside adrenal)
>autoimmune
>infective
>secondary tumor
>infiltration
>congenital adrenal hyperplasia
>drugs (eg etomidate)

② secondary due to pituitary
>congenital
>tumours
>infection
>trauma
>iatrogenic
>vascular lesions

198
Q

Causes of primary hyperaldosteronism?

A

> idiopathic/bilateral adrenal hyperplasia
unilateral adenoma (Conns syndrome)
primary adrenal hyperplasia
aldosterone producing carcinoma

199
Q

How do you investigate primary hyperaldosteronism?

A

> plasma aldosterone:renin ratio
urine 18 hydroxycortisol
genetic CYP11B2 testing

200
Q

What causes secondary hyperaldosteronism?

A

Diuretics

201
Q

What is a phaeochromocytoma?

A

A tumor releasing catecholamines

202
Q

How do you investigate increased catecholamines?

A

> plasma free metadrenalines
urinary fractionated matadrenalines

203
Q

Classify Congenital adrenal hyperplasia

A

Classic = early onset

No classic = late onset

204
Q

What is the pathophysiology of congenital adrenal hyperplasia?

A

21 alpha hydroxylase deficiency is the most common cause = decreased aldosterone and increased androgens

205
Q

Who should have a TFT?

A

① symptomatic
> fam hx
> features of thyroid disorder
> elderly with non-specific symptoms
> women in menopause with nonspecific sx
> pt taking myroxine

② pts at risk
> presenting with dm
> autoimmune disease
> treated hyperthyroidism
> down + Turner’s syndrome
> lithium + amiodarone

206
Q

What is the proteins that T3 and T4 bind to in the plasma?

A

Thyroxine binding globulin
Albumin
Transthyretin

207
Q

Mechanism of action of thyroid hormones

A

T4 and T3 dissociate from protein in plasma to cross the cell membrane and enter the nucleus where they promote mRNA and protein synthesis

208
Q

What drugs affect thyroid function?

A

> steroids and dopamine - decrease TSH secretion
lithium, iodine, amiodarone - decrease thyroid hormone secretion, induce hyperthyroidism
PPI’s
oestrogens

209
Q

Causes of low TSH in euthyroid patient?

A

> subclinical hyperthyroidism
treated hyperthyroidism
no thyroid all illness
pregnancy
ophthalmic Graves’ disease
treatment with dopamine or high dose steroids

210
Q

Causes of high TSH in euthyroid patient?

A

> subclinical al hypothyroidism
recovery phase of non-thyroidal illness

211
Q

When is TSH a good first line test vs when is it not a good first line test?

A

First line TSH okay
>asymptomatic patients
>monitoring pts on thyroxine

First line TSH not okay
>symptomatic patient not treated
>optimising tax in hyper or hypothyroidism
> screening and monitoring in pregnancy
>diagnosisi and monitoring of hypopituitarism
>diagnosis of TSHoma and Thyroid hormone resistance

212
Q

How do you treat hypothyroidism?

A

T4 treatment (to normalise TSH (neg feedback) and to relieve sx of patient)

Annual follow up

Wait 6-8weeks before lab tests after changing dose

213
Q

Classify causes of hypothyroidism?

A

Congenital
>thyroid aplastic
>dyshormogenesis

Acquired
>primary
• iatrogenic
° inflammatory ( autoimmune/transient)
>secondary
•hypopituitism
o iodine deficiency
• hypothalamic dysfunction

214
Q

When do you treat subclinical hypothyroidism?

A

> if TSH >10
if TSH 4.5-10 but positive anti-TPO antibodies

215
Q

Classify the causes of hyperthyroidism

A

> inflammatory (graves/thyroiditis)
toxic multinodular goitre
TSH-Oma
iodine induced ( toxic high intake of iodine in pts with autonomously functioning thyroid gland)
trophoblastic

216
Q

How do you manage hyperthyroidism?

A

> radioiodine
carbimazole
thyroidectomy

Measurement of TSH not reliable in first 4-6months

217
Q

What other lab tests are affected by hyperthyroidism?

A

> impaired glucose tolerance
hypocholesterolaemia
hypercalcaemia
abnormal LFT’s
increased SHBG

218
Q

What other lab tests are affected by hypothyroidism?

A

> hyponatraemia
hypercholesterolaemia
hyperprolactinaemia
increased CK
deceased SHBG

219
Q

When are thyroid function tests unreliable?

A

> nonthyroidal illness (thyroid abnormality twice as likely to be due to illness)
recovering from nonthyroidal illness
neonate (spike at birth and then gradual decrease)
pregnancy (trimester related reference ranges)

220
Q

Causes for abnormal results in euthyroid patients

A

> abnormal TBG
genetic variants of albumin
assay interference

221
Q

How do testes make testosterone? (Precursor and enzyme)

A

The enzyme 17B-HSD (17B hydroxysteroid dehydrogenase) converts androstenedione to testosterone

222
Q

What is the active form of testosterone?

A

Dihydrotestosterone (5 alpha reductase)

223
Q

What are the results of leydig cell dysfunction?

A

Decreased masculinisation and decreased sperm count

224
Q

What are the results of serotonin cell dysfunction?

A

Normal masculinisation but decreased sperm count

225
Q

Signs and symptoms of androgen deficiency?

A

> delayed puberty
decreased masculinisation
infertility
decrease bone mineral density
ED
reduced sexual desire
gynaecomastia
small testes
insulin resistance and T2 DM

226
Q

First line tests for suspected androgen deficiency?

A

Total serum testosterone (FASTING at 9am)
LH
FSH

227
Q

What are the sx experienced at different levels of testosterone?

A

<13 =decreased vitality and vigour
<11 =decreased morning erections
<8,5 =ED
<8 =decreased sexual thoughts

228
Q

When must free testosterone be measured?

A

When there is a decrease SHBG

> obesity
DM
nephrotic syndrome
steroids
hypothyroidism
acromegaly
polymorphisms in SHBG gene

When there is an increased SHBG (decreases free testosterone)
>aging
>HIV
>cirrhosis and hepatitis
>oestrogen use
>hyperthyroidism

229
Q

Second line tests for suspected hypogonadism?

A

> HCG stimulation test (Hypo-thalam pituitary axis)
stimulates leydig cells to increase testosterone (differentiate primary and secondary) = no response =primary testicular failure

> semen analysis

230
Q

How do you treat testosterone deficiency

A

Testosterone replacement therapy (IM or implant)
Goal = 10-15nmol/L

231
Q

What are the functions of oestrogens?

A

> female sexual characteristics (body shape, fat, hair pattern)
Prepare for pregnancy
maintenance of pregnancy
preparation for lactation

232
Q

Functions of progesterone

A

> promotes implantation
decreased contractility of uterine muscle
decrease maternal immune response

233
Q

What hormone indicates hypogonadism in females and how does it present?

A

Decreased 17B estradiol

Oligo/amenorrhoea

234
Q

How do you test for uterine dysfunction?

A

Progesterone challenge test (try and elicit withdrawal bleed = only if adequately oestrogenized)

235
Q

What is the pathophysiology of PCOS?

A

Ovaries produce excessive androgens = hyperandrogenism

236
Q

Differential diagnosis for hirsutism?

A

Ovarian
>PCOS
>androgen secreting tumor
>post-menopausal

Adrenal
>congenital adrenal hyperplasia
>Cushing syndrome
>androgen secreting tumors

iatrogenic
>androgens
>pRogesterones

237
Q

What is the Ferriman Gallwey score?

A

Used to score abnormal hair patterns
>8 = abnormal

238
Q

Menopause pathophysiology

A

Increase FSH, Low oestrodiol
- osteoporosis

Adverse lipid changes = decrease HDL, increase LDL
Adrenal androgens take over

239
Q

What is Kallman Syndrome?

A

Neurodevelopmental disorder caused by abnormal migration of olfactory and GnRH neurons through cribiform plate = by decreased GnRH leading to hypogonadism and anosmia.

Results in decreased FSH, LH, and testosterone.

240
Q

Treatment of Kallmans syndrome?

A

Testosterone replacement therapy

241
Q

Kleinefelter syndrome

A

XXY

decreased testosterone, increased FSH,LH and oestrogen

= gynaecomastea, tall, female body type

242
Q

What is the pathology in osteomalacia and rickets?

A

Decreased mineralisation of bone, most commonly due to decreased supply of calcium

243
Q

Causes of osteomalacia and rickets

A

Calciopenic
>nutritional calcium/VitD deficiency
>CKD
>anticonvulsants

Phosphopenic
>isolated phosphate loss
>generalized renal tubular disorders (Fanconi syndrome, renal tubular acidosis, hypophosphataemic rickets)

244
Q

What is the function of fibroblast growth factor 23?

A

Inhibits calcitriol
Stimulates renal phosphate loss

245
Q

What is hypophosphatasia?

A

A rare inherited disorder with features that resembles rickets in which the ALP is decreased.

246
Q

Clinical features of osteomalacia and rickets?

A

Bone pain
Bone deformities
Proximal muscle weakness

247
Q

Management of osteomalacia and rickets

A

Vit D supplementation

Ca and PO4 supplementation
Monitor ALP, PTH, Ca and phosphate = should normalise

248
Q

What is osteoporosis?

A

Decrease in bone mass and abnormal micro architecture

BMD >2.5 std deviations below the mean, or by a pathological fracture

249
Q

Pathology of osteoporosis

A

Increased osteoclast activity
Decreased osteoblast activity

250
Q

How do you diagnose osteoporosis?

A

DEXA
WHO frax tool to estimate future risk of fracture with clinical knowledge and BMD

251
Q

Bone remodelling process

A

Bone lining cells line quiescent bone surfaces. These cells are replaced by osteoclasts which reabsorb the bone. Once they are done, they apoptoses and are replaced by osteoblasts which lay down new osteoid 6-12 months)

252
Q

What are markers of bone resorption

A

Collagen derivatives
>pyridinium cross links of collagen (urine)
>cross linking telopeptides of Type 1 collagen (serum)

253
Q

Name markers of bone formation

A

> plasma osstoclacin
bone specific ALP
procollagen type 1 terminal peptides

254
Q

What is the use of bone turnover markers?

A

Monitoring treatment and adherence
NOT diagnosing

255
Q

What is pagets disease of bone

A

It is a disease of unknown aetiology caused by increased osteoclastic resorption if bone and the new bone that replaced it is disorganised
=deformed, painful bone

256
Q

What blood test result is common in pagets?

A

Increased ALP
normal calcium and phosphate

257
Q

What is CKD-MBD

A

Chronic kidney disease with mineral and bone disorder

258
Q

Pathogenesis of CKD BMD

A

Decrease of nephrons leads to hyperphosphataemia. This causes a increase FBF23 and the. A decrease calcitriol synthesis = hypocalcaemia

Hypocalcaemia causes increased PTH (increases phosphate excretion but limited by poor kidney function)

Phosphate becomes so high that it exceeds solubility and phosphate and calcium form metastatic calcification.

259
Q

How do you manage CKD BMD

A

Monitor calcium and phosphate, PTH, ALP
Oral phosphate binder
Oral calcitriol
PTH maintained at 2-4x normal

Chemical Pathology (8 decks)

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