Biochemistry

Question 1

Causes of metabolic acidosis.

UKSLAMS

Answer 1

Uraemia.
Ketoacidosis.
Salicylates.
Lactic acidosis.
Alcohol.
Methanol.
Sepsis.

Question 2

Causes of increased anion gap?

ASIDE

Answer 2

Acidosis (lactic).
Salicylates.
Intoxication.
Diabetic ketoacidosis.
Ethylene glycol.

Question 3

Causes of low anion gap.

Answer 3

Hypoalbuminaemia - hepatic or renal disease, malnutrition.
Lithium toxicity.
Multiple myeloma.

Question 4

Causes of hypercalcaemia?

Answer 4

• Malignancy (e.g. prostate cancer).
• Primary, tertiary hyperparathyroidism.
• Sarcoidosis.
• Myeloma.
• Vitamin D excess.

Question 5

How is hypercalcaemia managed?

Answer 5

• IV 0.9% normal saline.

- Bisphosphonates.

Question 6

What is the mechanism of action of bisphosphonates in hypercalcaemia?

Answer 6

Act over 48 hours to prevent bone resorption and inhibit osteoclasts.

Question 7

Describe the electrolyte abnormalities that would support a diagnosis of Vitamin D deficiency.

Answer 7

• Hypocalcaemia.
  (Vitamin D deficiency causes decreased calcium absorption from intestines and decreased renal reabsorption).
• Low serum phosphate.
  (Due to secondary hyperparathyroidism > phosphaturia).
• Elevated ALP.
  (Due to secondary hyperparathyroidism > increased bone turnover).
• Low 25-(OH) D3.
• Low or normal magnesium (never high - Mg and Ca2+ levels correlate - unsure why).

Question 8

ECG features of hyperkalaemia?

Answer 8

• Peaked T waves.
• PR prolongation.
• QRS widening.

Question 9

ABG showing pH 7.2, PaCO2 8.0, PaO2 18, HCO3 24, base excess of -0.5. What is the abnormality?

Normal ranges:

• pH 7.35 - 7.45.
• PaCO2 4.6-6.0 kPa.
• PaO2 10.5-13.5 kPa.
• HCO3 24-30mmol/l.
• Base excess -2 to +2 mmol/l.

Answer 9

Respiratory acidosis.

low pH - acidosis.

• High CO2.
• Base excess and bicarbonate within normal limits.