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Path 2022 > Chem Path > Flashcards

Chem Path Flashcards

1
Q

Normal blood pH

A

7.35-7.46

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2
Q

Causes of metabolic acidosis

A

o Increased H+ production e.g., DKA
o Decreased H+ excretion e.g., renal tubular acidosis
o Bicarbonate loss e.g., intestinal fistula

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3
Q

Causes of respiratory acidosis

A

o Decreased ventilation
o Poor lung perfusion
o Impaired gas exchange

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4
Q

Causes of metabolic alkalosis

A

o H+ loss e.g., pyloric stenosis
- Also a raised urea, creatinine, total protein (dehydration)
- Low potassium, low chloride
o Hypokalaemia
o Ingestion of bicarbonate

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5
Q

Causes of respiratory alkalosis

A

Hyperventilation due to:

o Voluntary e.g., anxiety
o Artificial ventilation
o Stimulation of respiratory centre

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6
Q

Cystic Fibrosis diagnostic Ix (in neonate)

A

High blood immune reactive trypsin (IRT)

If IRT >99.5th centile in 3 bloodspots –> do 4 panel DNA mutation analysis
• 2 mutations = CF
• 1 mutation = 28 panel analysis
• 0 mutations = may repeat IRT at 21-28 days if IRT>99.9th centile

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7
Q

Specificity & sensitivity calculations

A

Sensitivity = true positive / total disease present

Specificity = true negative / total disease absent

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8
Q

Predictive value calculations

A

Positive predictive value = true positive / total positive
- NOTE: PPV depends on disease prevalence/incidence too!

Negative predictive value = true negative / total negative

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9
Q

Presentation of Organic Acidurias in neonate

A 
Unusual odour e.g. cheesy/sweaty smell (in isovaleric academia)
Lethargy
Feeding problems
Truncal hypotonia / limb hypertonia
Myoclonic jerks
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10
Q

Differences in neonatal kidneys

A

Low GFR for surface area:

  • slow excretion of solute load
  • limited Na+ available for H+ exchange

Short proximal tubule –> low reabsorptive capability (but is usually enough for small filtered load)

Short Loops of Henle/distal collecting duct –> reduced ability to concentrate urine

Distal tubule relatively unresponsive to aldosterone –> persistent loss of Na+

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11
Q

Causes of Hypernatraemia in neonates

A

Uncommon after 2 weeks

Usually dehydration

Rare causes:

  • Salt poisoning
  • Osmoregulatory dysfunction
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12
Q

Most important cause of HYPOnatraemia in neonate

A

Congenital adrenal hyperplasia

lack of 21 hydroxylase

  • -> build up of 17-OH progesterone
  • -> absence of aldosterone + cortisol
Signs/Sx:
o	Hyponatraemia
o	Hyperkalaemia
o	Marked volume depletion
o	(+ hypoglycaemia)
o	Ambiguous genitalia in female neonates
o	Growth acceleration in older child
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13
Q

Causes of high UNCONJUGATED bilirubin in neonate

A

Early rise:

  1. High level of synthesis (RBC breakdown)
    - Haemolytic disease – ABO, Rhesus incompatibility
    - G6PD deficiency
    - Crigler-Najjar syndrome
  2. Low rate of transport into liver and 3. Enhanced enterohepatic circulation
    - Biliary atresia, choledocal cyst
    - Ascending cholangitis in TPN
    - Inherited metabolic disorders

Prolonged jaundice (<14 in term, >21 in preterm)

  • Prenatal infection / sepsis / hepatitis
  • Hypothyroidism – screened at day 6-8 (Guthrie?)
  • Breast milk jaundice
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14
Q

Key features Acute intermittent porphyria

A

Neurovisceral attacks

  • abdo pain
  • SIADH & hyponatraemia
  • seizures
  • sensory loss / muscle weakness

NO SKIN LESIONS

Precipitated by:

  • medications: barbiturates, steroids, anti-convulsants
  • alcohol
  • stress: surgery, infection
  • reduced calorie intake
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15
Q

Other Acute porphyrias (not acute intermittent)

A

Hereditary Coproporphyria
Variegate Porphyria

Both have acute neurovisceral attacks + skin lesions

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16
Q

Non-acute porphyrias

A

Congenital eryrthopoietic porphyria

  • only skin lesions: blistering, fragility, pigmentation, erosions
  • associated with Myelodysplasic syndromes

Porphyria cutanea tarda

  • skin lesions: vesicles on sun exposed areas, crusting, superficial scarring, pigmentation
  • PCT-like syndrome can be caused by hexachlorobenezene

Erythropoietic protoporphyria (EPP)

  • skin lesions: NO BLISTERS, photosensitivity, burning, itching oedema after sun exposure
  • associated with myelodysplastic syndromes
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17
Q

Important requirement for urine samples if suspecting acute porphyria

A

Protect from light!

Otherwise, Porphyrinogens oxidised to porphyrins then –> activated porphyrins + O2

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18
Q

Ix results in sick euthyroid

A

o Low T4 (when severe)
o High normal TSH (later becomes low)
o Low T3 and reduced T3 action

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19
Q

Ix results in subclinical hypothyroidism

A

High TSH
Normal free T4

TPO autoantibodies - if positive, can predict future thyroid disease

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20
Q

Ix results in thyrotoxicosis

A
  • Low TSH
  • High free T4, free T3
  • Technetium scan - identify specific cause e.g. single toxic adenoma
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21
Q

Hyperthyroid treatment options

A

Beta blocker (if pulse >100)

Radioactive iodine
- Do NOT use if active thyroid ophthalmopathy

Surgery
- +/- potassium perchlorate before hand to prevent iodide uptake

Thionamides - e.g. Carbimazole, Propylthiouracil

  • Block & replace OR titration regimes
  • NOTE: can cause agranulocytosis - warn pt to stop meds if any sore throat/fever and check FBC!
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22
Q

Vitamin Deficiencies

A

A/retinol - Colour blindness
D/cholecalciferol - Osteomalacia/rickets
E/tocopherol - Anaemia, neuropathy, ?malignany/IHD
K/phytomenadione - Defective clotting

C/ascorbate - Scurvy
Folate - megaloblastic anaemia, NTDs
Niacin - pellagra

Iron - hypo chromic anaemia
Iodine - Goitre, hypothyroidism
Zinc - dermatitis
Copper - anaemia
Fluoride - dental caries
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22
Q

Vitamin Deficiencies

A

A/retinol - Colour blindness
D/cholecalciferol - Osteomalacia/rickets
E/tocopherol - Anaemia, neuropathy, ?malignany/IHD
K/phytomenadione - Defective clotting

C/ascorbate - Scurvy
Folate - megaloblastic anaemia, NTDs
Niacin - pellagra

Iron - hypo chromic anaemia
Iodine - Goitre, hypothyroidism
Zinc - dermatitis
Copper - anaemia
Fluoride - dental caries
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23
Q

Disorders of protein malnutrition

A 
Marasmus
• Shrivelled
• Growth retardation
• Severe muscle wasting
• No subcutaneous fat

Kwashiorkor
• More common at times of famine – carbohydrate remains but protein content reduced
• Scaling/ulcerated
• Lethargic
• Large liver, subcutaneous fat
• Protein deficient
• Oedematous
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24
Causes of SIADH
* CNS pathology – stroke, haemorrhage, tumour * Lung pathology – pneumonia (esp Legionella), pneumothorax * Drugs – SRRIs, TCA, opiates, PPIs, carbamazepine * Tumours * Surgery * Acute intermittent porphyria
25
Treatment of hyponatraemia
If hypovolaemic: Volume replacement, 0.9% saline If euvolaemic: Fluid restrict <750ml/day + Abx infusions + Treat underlying cause - E.g. hydrocortisone + fludrocortisone in Addison's - E.g. levothyroxine in hypothyroidism - E.g. Demeclocycline or Tolvaptan in SIADH If Hypervolaemic = Fluid restrict <750ml/day + Treat underlying cause + Abx infusions If severe (reduced GCS, seizures) = hypertonic 3% saline + seek expert help
26
The risk of rapid increase in serum sodium?
Central Pontine Myelinolysis should not increase Na by more than 8-10mmol/L in first 24 hours Osmotic shifts cause stretching of BBB endothelial cells --> inflammatory signals Presents with: - quadriplegia - dysarthria - dysphagia - seizures, coma, death
27
Management of HYPERnatraemia
1. Fluid replacement – 5% Dextrose 2. Treat underlying cause 3. Take serial Na+ measurements every 4-6 hours If also hypovolaemic, give 0.9% saline to correct ECF depletion (alongside 5% dextrose to correct water deficit)
28
ECG changes in HYPERkalaemia
* Peaked T waves (Early) * Broad QRS * Flat P-wave * Prolonged PR (+ bradycardia) * Sine wave (latest)
29
Management of HYPERkalaemia
Tx if ECG changes of K+ ?6.5 * 10ml 10% calcium gluconate * 100ml 20% dextrose (previously 50ml 50% dextrose) + 10U insulin * Nebulised salbutamol * Treat underlying cause
30
Management of HYPOkalaemia
If K+ 3.0-3.5 • Oral potassium chloride – 2 x SandoK tablets TDS for 48 hours • Recheck serum K+ If K+ <3.0 • IV potassium chloride - Max rate 10mmol/hour • Rates >20mmol/hour = irritating to peripheral veins + Tx underlying cause
31
Management of HYPOkalaemia
If K+ 3.0-3.5 • Oral potassium chloride – 2 x SandoK tablets TDS for 48 hours • Recheck serum K+ If K+ <3.0 • IV potassium chloride - Max rate 10mmol/hour - Rates >20mmol/hour = irritating to peripheral veins + Tx underlying cause
32
Diagnostic findings in Conn's syndrome
HTN + Low K+ | High aldosterone:renin ratio (aldosterone suppresses renin)
33
Normal response to combined pituitary function test
``` Glucose drops <2mM then recovers Cortisol reaches 450-550nM (>400) Growth hormone >10IU/L LH, FSH, TSH >10IU/L Prolactin stimulation ```
34
Treatment of (functioning) prolactinoma
``` Urgent hydrocortisone (Fludrocortisone not needed - adrenals make aldosterone independent of hypothalamic-pituitary axis) ``` Other hormone replacement: - levothyroxine - oestrogen - GH - + Dopamine agonist e.g., Cabergoline or Bromocriptine to shrink prolactinoma
35
Clinical features of Acromegaly
* Headaches * hyperhidrosis * Large hands “spade like” * Prominent supraorbital ridges * Increased interdental spaces * Macroglossia * Prognathism * Bitemporal hemianopia * Often presents alongside increased prolactin?
36
Diagnostic Ix for Acromegaly
IGF-1 measurement = raised Oral glucose tolerance test = paradoxical growth hormone rise after glucose given MRI pituitary = visualise any adenoma
37
Treatment of acromegaly
``` Trans-sphenoidal surgery (if no lateral growth or involvement of blood vessels) +/- Pituitary radiotherapy D2 receptor agonist e.g. Cabergoline Somatostatin analogues e.g. Octreotide GH receptor antagonist e.g. Pegvisomant ```
38
Osmolality equation
* (Na+, K+) + (Cl-, HCO3-) + Urea + Glucose | * OR just 2 x (Na+, K+) + Urea + Glucose – since do not know anion levels!
39
Anion gap equation
Na + K - Cl – HCO3 | Normal range = 16-20mM
40
Diagnostic findings in DKA
Hyperglycaemia >11.0mmol/L Ketonaemia >3.0mmol/L OR significant ketonuria (2+ on dip) Acidosis HCO3- <15.0mmol/L AND/OR venous pH <7.3
41
MOA of diabetes drugs
Gliptins e.g., sitagliptin = DPP-4 inhibitors Thiazolidinediones / glitazones e.g., Pioglitazone = bind to peroxisome proliferator activated receptor-gamma in adipocytes --> maturation of fat cells + reduced circulating fat --> improved insulin sensitivity Biguanides e.g. metformin = inhibit conversion of lactate to glucose in liver
42
T2DM diagnostic criteria
Fasting plasma glucose > 7.0mM OR Glucose tolerance test (75 grams given at time 0) plasma glucose > 11.1mM at 2 hours OR HbA1c > 48 NOTE: impaired glucose tolerance is 2-hour value 7.8-11.1mM OR HbA1c >42
43
Summary of adrenal disease
Addison's - low Na - high K+ - hypotension - Ix = short SynACTHen --> low cortisol - Tx = corticosteroid replacement Phaeo - HTN - Ix: urine + serum metanephrines (catecholamines, normetanephrines) - Tx = alpha blockade, beta blockade, surgery Conn's - high Na - low K - HTN - Ix: HIGH aldosterone: renin ratio - Tx: adrenalectomy OR aldosterone antagonist Cushing's - centripetal obesity, inter scapular fat pad, bruising etc. - DM, HTN - low K - Ix: - - 9am + 12am plasma cortisol --> HIGH - - low dose dexamethasone suppression test --> not suppressed - - IPSS (pituitary sampling) to identify cause - Tx: Treat cause e.g. stop steroids, remove tumour
44
Normal GFR
120mL/min
45
Diagnostic criteria for AKI
* Increase in serum creatinine by >26mmol/L within 48 hours OR * Increase in serum creatinine to 1.5x baseline within 7 days OR * Urine output <0.5ml/kg/hour for 6 hours
46
Stages of AKI
Stage 1 - Increase in serum Cr by ≥26 micromol/L OR by 1.5 to 1.9x the ref serum Cr - UO <0.5ml/kg/hour for 6-12 hours Stage 2 - Increase in serum Cr by 2-2.9x ref serum Cr - URO <0.5ml/kg/hour for ≥12 hours Stage 3 - Increase in serum Cr by ≥354micromol/L OR ≥3x ref serum Cr - UO <0.3ml/kg/hour for ≥24 hours OR anuria for ≥12 hours
47
Pre-renal causes of AKI
Generalised reduction in tissue perfusion or selective renal ischaemia + failure of adaptive mechanisms to maintain renal percussion * true volume depletion * hypotension * oedematous states * selective renal ischaemia * drugs affecting glomerular blood flow - NSAIDs, calcineurin inhibitors, ACEi, ARB, diuretics
48
Renal causes of AKI
Abnormality of any part of nephron • Vascular disease – vasculitis • Glomerular disease – glomerulonephritis • Tubular disease – acute tubular necrosis (most common!) from untreated pre-renal AKI or endogenous/exogenous toxins • Interstitial disease – analgesic nephropathy
49
Post-renal causes of AKI
Physical obstruction to urine flow * Intra-renal obstruction * Ureteric obstruction – bilateral * Prostatic/urethral obstruction * Blocked urinary catheter
50
Indications for emergency dialysis in AKI
* (Metabolic) acidosis * Refractory hyperkalaemia * Lithium, aspirin ‘intoxication’ * Pulmonary oedema * Uraemic encephalopathy, pericarditis
51
Definition/Criteria for Chronic kidney disease
Abnormalities of kidney function ≥ 3 months with implications for health Longstanding decline in GFR (<60) OR 1 of: • Albuminuria / proteinuria • Urine sediment abnormalities e.g., haematuria • Electrolyte abnormalities • Histological abnormality • Structural abnormalities (on imaging) • Hx kidney transplant
52
Stages of CKD
G1: GFR >90 with evidence of kidney damage G2: GFR 60-89 G3a: GFR 45-59 G3b: GFR 30-44 G4: GFR 15-29 G5: GFR <15
53
Most common causes of CKD
* Diabetes!! * Atherosclerotic renal disease * HTN * Chronic glomerulonephritis * Infective or Obstructive nephropathy * Polycystic kidney disease
54
Progression of Uraemic cardiomyopathy (in CKD)
LV hypertrophy LV dilatation LV dysfunction
55
Indications for dialysis in CKD
``` o Intractable hyperkalaemia o Acidosis o Uraemic Sx – nausea, pruritis, malaise o Therapy-resistant fluid overload o CKD Grade 5 ```
56
Patterns of LFT abnormalities
High ALP + GGT (ALP >>) = biliary obstruction e.g. gallstones, HOP ca. GGT > ALP = recent ETOH intake ALP > GGT = pregnancy? osteomalacia (if PTH high), Paget's disease (if osteocalcin high) AST + ALT high = hepatocyte damage - AST rises most (>ALT) = alcoholic hepatitis / cirrhosis - ALT rises most (>AST) = viral hepatitis
57
Tumour markers
Ca125 = ovarian Ca19-9 = pancreatic, cholangiocarcinoma acid phosphatase / PSA = prostate CEA = colorectal AFP = testicular ca. (teratoma), hepatocellular ca.
58
Treatment of acute gout
NSAIDs colchicine - inhibits polymerisation of tubular --> less neutrophil motility --> less inflammation Glucocorticoids - oral or intra-articular injection Do NOT attempt to alter plasma urate concentration - can cause further precipitation of crystals!
59
Microscopy of crystal arthropathies
Gout (monosodium urate) - negative birefringence (yellow when parallel to compensator, blue when perpendicular) - needle shaped Pseudogout (calcium pyrophosphate) - weak positive birefringence (blue when parallel to compensator) - rod or Rhomboid shaped
60
Pathophysioloy & key features of Lesch Nyhan syndrome
X linked Complete deficiency of H(G)RPT enzyme No recycling of hypoxanthine or guanine to IMP/GMP Normal at birth BUT then - developmental delay, mental retardation - spasticity - hyperuricaemia - choreiform movements ~1 year - self mutilation, aged 1-16yrs (affects 85%)
61
Pathways of purine synthesis
De novo - metabolically difficult - inefficient Salvage - recycles purine catabolites - predominates in most tissues EXCEPT bone marrow - highly efficient
62
Rate limiting step of Purine Metabolism
PAT - Negatively regulated by AMP & GMP (end products of purine synthesis) - Also subject to positive feed-forward effect by PPRP
63
Transport of thyroid hormone
75% thyroid binding globulin 20% TBPA 5% Albumin 0.03% free T4

Path 2022 (12 decks)

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