Blood Tests

Question 1

List some causes of high Hb.

Answer 1

• Dehydration
• Diuretic therapy
• Secondary to anoxia (high altitude, hypoxic respiratory conditions, heavy cigarette smoking)
• Secondary cause e.g. polycythaemia rubra vera

Question 2

Name a cause of low and high Hct.

Answer 2

Low in any anaemia and high in polycythaemia.

Question 3

What does MCV stand for? What is MCH?

Answer 3

Mean corpuscular volume - average volume of patient’s RBCs. Helps to morphologically classify anaemia, dependent on its cause. Low = microcytic, normal = normocytic, high = macrocytic

Mean corpuscular haemoglobin - average haemoglobin content in an RBC. If low typically shows hypochromia. Can be seen in iron-deficiency and haemoglobinopathies.

Question 4

What diagnosis does MCHC aid with?

Answer 4

Mean corpuscular haemoglobin concentration (MCHC) – average haemoglobin concentration per RBC. Helps to classify microcytic anaemias. Low levels are typical of iron deficiency or thalassaemia; very high often reflect spherocytosis or RBC agglutination.

Question 5

What does high RDW suggest?

Answer 5

Red cell distribution width (RDW) – a measure of the variation in RBC size.

If high this suggests a large variation in sizes, seen in iron deficiency, myelodysplastic syndrome and haemoglobinopathies.

Question 6

List some causes of thrombocytosis.

Answer 6

Reactive:

• Blood loss
• Infection
• Inflammation
• Post-splenectomy

Autonomous:

• Genetic abnormalities
• Malignancies

Question 7

List some causes of thrombocytopenia.

Answer 7

• Drugs
• Foods
• Infections
• Liver disease e.g. hypersplenism
• Alcohol
• Nutrient deficiency
• Pregnancy
• Bone marrow disorder
• Inherited
• Bleeding - platelets initiate mechanisms that repair injury to thr vascular endothelium. Can be high (thrombocytosis) or low (thrompocytopenia)

Question 8

What type of infections are these cells most commonly associated with?

• Neutrophils
• Lymphocytes
• Monocytes
• Eosinophils
• Basophils

Answer 8

• Neutrophils - bacterial
• Lymphocytes - viral
• Monocytes - chronic infection
• Eosinophils - allergies/parasites
• Basophils - viral/urticaria

Question 9

List 3 causes of neutrophilia and neutropenia.

Answer 9

Neutrophilia

• bacterial infection
• steroids
• post-surgery
• burns
• vasculitis
• neoplasia

Neutropenia

• infection
• drugs (chemo)
• autoimmune e.g.CTD, hereditary

Question 10

List 3 causes of lymphocytosis and lymphopenia.

Answer 10

Lymphocytosis

• reactive (viral infection, stress)
• metabolic syndrome
• primary (malignancies)

Lymphopenia

• steroids
• immunosuppressive agents
• AI disease

Question 11

List 3 causes of monocytosis.

Answer 11

• Chronic infection (TB, syphilis)
• IBD
• carcinomas
• myelodysplastic syndromes

Question 12

List 3 causes of eosinophilia.

Answer 12

• allergy
• neoplastic
• CTD
• parasitic infection

Question 13

List 3 causes of basophilia.

Answer 13

• Viral infection
• Urticaria
• Hypothyroidism
• Post-splenectomy
• UC

Question 14

What information is found through requesting U&Es?

Answer 14

Sodium, potassium, chloride, urea, creatinine

Common to also get eGFT reported

Question 15

What are the normal ranges for sodium?

Answer 15

135-145

Hyponatraemia:

• Na < 135; Mild:
• 130-134, Moderate:
• 120 -129, Severe <120

Hypernatraemia:

• Na >145

Question 16

Is sodium an intra/extracellular ion? How is its concentration maintined?

Answer 16

Extracellular

It is closely linked to fluid as water follows solutes by osmosis. Sodium reabsorption is increased by aldosterone in the DCT. ADH causes reabsorption of water (alone) from the collecting duct.

Question 17

How can you divide the causes of hyponatraemia? Why can it be fatal?

Answer 17

Into hypovolaemia, euvolaemia, hypervolaemia.

It can develop rapidly and water can shift into the brain causing cerebral oedema.

Question 18

Summarise the 2 causes of hyponatraemia in hypo/eu/hypervolaemia.

Answer 18

Hypovolaemia = Na lost and H₂O follows

Na loss from kidneys:

• -Addison’s Disease
• -Diuretics
• -Kidney Injury
• -Osmotic diuresis

Na loss from elsewhere:

• -Diarrhoea and vomiting
• -Burns
• -Fistula

Euvolaemia = Normal Na quantity, H₂O gained

• SIADH
• Hypothyroidism
• Glucocorticoid insufficiency
• Water intoxication

Hypervolaemia = Excess ADH released secondary to intravascular fluid depletion (due to extravasation)

• CCF
• Hypoalbuminaemia e.g. cirrhosis, nephrotic syndrome

Question 19

List two causes of hypernatraemia in hypo/euvolaemia.

Answer 19

Hypovolaemia

• Fluid loss
  
  • Burns
  • Diarrhoea and vomiting
• Diabetes insipidus
• Osmotic diuresis

Euvolaemia

• Iatrogenic
  
  • Excess IV crystalloid
  • Sodium containing drugs

Question 20

What are the normal ranges of potassium? Is it mostly intra/extracellular?

What increases potassium uptake and excretion?

Answer 20

3.5- 5.0 (4.2 is normal) - levels outside this can have cardiac effects.

90% intracellular ion

• Uptake - insulin and catecholamines
• Excretion - aldosterone

Question 21

List 2 causes of hypokalaemia caused by:

• increased renal excretion
• increased cellular uptake
• other loss

Answer 21

Increased renal excretion

• Thiazide or loop diuretics
• Endocrine - steroids, Cushing’s, Conns
• RTA - hypomagnasaemia

Increased cellular uptake

• Salbutamol
• Insulin
• Alkalosis

Other loss:

• Intestinal fluid loss
• Burns
• Malnutrition

Question 22

What are the ranges for mild moderate and severe hyperkalaemia? What causes pseudohyperkalaemia?

Answer 22

K>5.5;

• Mild: 5.5-5.9,
• Moderate: 6.0-6.4,
• Severe: >6.5 mmol/L.

Note can also be pseudohyperkalaemia due to haemolysis.

Question 23

What are the causes of hyperkalaemia caused by

• Reduced renal excretion
• Increased cellular release
• Excess load

Answer 23

Reduced renal excretion

• Acute/chronic kidney injury
• Drugs (K sparing diuretics, ACEi, NSAIDs)
• Addisons

Increased cellular uptake

• Acidosis
• Tissue breakdown e.g. rhabdomyolysis

Excess load

• Iatrogenic
• Massive blood transfusion

Question 24

How is urea formed in the body? List 3 causes of a low and high urea.

Answer 24

Urea is formed when ammonia is converted in the liver, and then excreted in the kidneys. It is raised in kidney injury however urea is not specific for kidney disease as there are other causes of abnormal urea.

Causes of high urea:

• dehydration,
• GI bleed,
• increased protein breakdown (surgery, trauma, infection, malignancy),
• high protein intake,
• drugs

Causes of low urea:

• malnutrition,
• liver disease,
• pregnancy

Question 25

What is creatinine a waste product of?

Answer 25

Creatinine is a waste product of the breakdown of creatine phosphate. It is excreted in the kidneys and is specific for kidney injury (but baseline depends on muscle mass).

Question 26

How is AKI defined?

Answer 26

An Acute Kidney Injury is when Creatinine rises ≥50% of baseline within 7 days or ≥26μmol/ in 48 hours (or urine output is \<0.5ml/kg/hr ≥ 6 hours).

Question 27

What is ALT? What are the normal ranges?

Answer 27

**Alanine Transferase (ALT)** is a cytosolic enzyme, which is expressed predominantly in liver cells and is used as a marker to assess liver cell damage. ALT \< 120 IU/L: generally considered mild ALT \> 120 IU/L: generally considered severe

Question 28

List 3 common causes of raised ALT.

Answer 28

Common causes: * Alcohol * Viral hepatitis * Steatosis * MEdications toxins e.g. NSAIDs, antibiotics, statins, antiepileptics, antituberculosis drugs Less common: * AI hepatitis * Haemochromatosis * Alpha-1 antitrypsin deficiency * Wilson's disease Non-hepatic causes of raised ALT (usually small) * Coeliac * Strenuous exercise * Muscle disease * Endocrine disease e.g. Hypo/hyperthyroidism

Question 29

What is AST? How can it be helpful alongside ALT? Is it better than ALT? Where is it found in the cell?

Answer 29

**_Aspartate Aminotransferase (AST)_** **Ratio of AST to ALT** may provide useful information about the possible cause of liver disease: AST:ALT ratio **≥ 2.1 may be suggestive, but not diagnostic of alcohol related liver disease**, while AST:ALT ratio **\< 2.1 may suggest hepatic steatosis or chronic viral hepatitis.** AST is expressed in the liver, as well as in the heart, skeletal muscle, kidneys, brain and red blood cells and therefore is not as liver specific as ALT. ALT is predominantly cytoplasmic and **AST is present in both cytoplasm and mitochondria**

Question 30

What is ALP? Where is it found?

Answer 30

**Alkaline Phosphatase (ALP)** The two main sources of ALP are liver and bone, although there are also intestinal and placental isoforms. Elevations may be physiological or pathological.

Question 31

List 3 physiological and pathological causes of a raised ALP?

Answer 31

_Physiological:_ * Third trimester of pregnancy * Adolescents, due to bone growth * Benign, familial _Pathological:_ * Bile duct obstruction * Primary biliary cirrhosis * Primary sclerosing cholangitis * Drug induced cholestasis, e.g. anabolic steroids * Metastatic liver disease * Bone disease e.g. Paget’s * Heart failure

Question 32

What is GGT a good marker for? What is a disadvantage?

Answer 32

**Advantage**/_disadvantage_ ## Footnote Gamma-Glutamyl Transferase (γGT) is a **sensitive marker for hepatobiliary disease,** but its use is limited by _poor specificity_ The use of γGT is in **supporting a hepatobiliary source for other raised liver enzymes, e.g. ALP**. _It has limited utility as a primary liver test._ If an isolated raised γGT is found, consider retesting after 3m if mildly raised (5x ULN). Consider ultrasound if γGT is \>5x ULN.

Question 33

List some causes of raised GGT.

Answer 33

* Hepatobiliary disease (often with other liver enzyme abnormalities) * Pancreatic disease * Alcoholism * Chronic obstructive pulmonary disease * Renal failure * Diabetes * Myocardial infarction * Drugs, e.g. carbamazepine, phenytoin and barbiturates and oral contraceptive pill

Question 34

Apart from LFTs which tell us about liver/bile duct damage, which tests can we do to assess liver function?

Answer 34

* Haem breakdown – Bilirubin * Plasma proteins – Albumin * Clotting factors - PT/INR * Portal system – platelets