Endocrinology and Metabolism
The exam tests the emergencies (diabetic ketoacidosis, hyperosmolar state, thyroid storm, adrenal crisis), the interpretation of paired hormone and gland tests, and safe chronic prescribing. Most marks are lost by treating a laboratory value without checking volume status or the paired hormone.
Diabetic emergencies
- Diabetic ketoacidosis: glucose usually above 250 mg/dL, pH below 7.30, bicarbonate below 18, ketonaemia, raised anion gap. Treatment is isotonic saline, intravenous insulin infusion at 0.1 unit/kg/h, potassium replacement once potassium is below 5.5 with adequate urine output, and dextrose added when glucose falls near 200 mg/dL to allow continued insulin.
- Hyperosmolar hyperglycaemic state: glucose often above 600 mg/dL, osmolality above 320, minimal ketosis, profound dehydration and altered consciousness. Fluid replacement and slower glucose correction matter more; cerebral oedema is a risk with over-rapid correction.
- Never stop the insulin infusion abruptly; overlap with subcutaneous insulin before stopping.
Thyroid and adrenal
- Primary hypothyroidism: high TSH with low free T4. Subclinical: high TSH with normal free T4. Pituitary disease: low or inappropriately normal TSH with low free T4.
- Adrenal crisis presents with hypotension, hyponatraemia, hyperkalaemia, hypoglycaemia and pigmentation. Draw a cortisol sample if it does not delay treatment, then give intravenous hydrocortisone 100 mg immediately with saline.
- Thyrotoxicosis: TSH suppressed; use free T4 (and T3) to grade severity. Thyroid storm is clinical: fever, tachyarrhythmia, agitation, gastrointestinal upset; treat with a beta-blocker, thionamide, iodine after the thionamide, and steroid.
Calcium and pituitary clues
- Correct calcium for albumin (add 0.8 mg/dL for every 1 g/dL albumin below 4). High calcium with inappropriately normal or high PTH suggests primary hyperparathyroidism; suppressed PTH suggests malignancy.
Worked example
A 22-year-old with type 1 diabetes has vomiting, glucose 420 mg/dL, pH 7.12, bicarbonate 9, and potassium 5.8 with normal urine output. Give saline, start the insulin infusion, defer potassium until it falls below 5.5, add dextrose when glucose reaches 200 mg/dL, and look for the precipitant (infection, missed insulin, myocardial infarction).
Traps
Giving bicarbonate routinely in ketoacidosis; starting potassium replacement at a potassium of 5.8; giving iodine before a thionamide in thyroid storm; and diagnosing adrenal insufficiency on a random cortisol taken during acute stress without interpreting it in context.