Endocrinology, Diabetes and Metabolism
Core concepts
Cover thyroid disease (TSH as first-line test; primary hypothyroidism shows high TSH and low free T4; Graves disease shows suppressed TSH with diffuse uptake), adrenal disorders (primary adrenal insufficiency with hyperpigmentation and hyperkalemia; Cushing syndrome with dexamethasone suppression testing), pituitary disease, calcium metabolism (primary hyperparathyroidism vs malignancy-related hypercalcemia), and diabetes diagnosis and management (HbA1c ≥6.5%, fasting glucose ≥7.0 mmol/L, 2-hour OGTT ≥11.1 mmol/L). Know DKA and HHS management: fluids, insulin infusion, potassium replacement, and avoidance of cerebral edema.
Traps
Examiners test the "check potassium before insulin" rule in DKA and the fact that total body potassium is depleted even when serum potassium is normal or high. Beware of thyroid storm (Burch-Wartofsky) and myxedema coma as emergencies. In hypercalcemia, a suppressed PTH points to malignancy; an elevated PTH points to primary hyperparathyroidism. Remember that subclinical hypothyroidism (high TSH, normal free T4) does not always require treatment.
Worked rule of thumb
DKA: start isotonic fluids, then insulin infusion once potassium is ≥3.3 mmol/L; add potassium to fluids when serum K is <5.5; monitor glucose hourly and add dextrose when glucose <14 mmol/L to continue insulin clearance of ketones.
Key points
- TSH is the best initial thyroid test.
- Primary adrenal insufficiency: hyperkalemia, hyponatremia, hyperpigmentation.
- Check potassium before starting insulin in DKA.
- PTH level distinguishes hypercalcemia causes.
- HbA1c ≥6.5% is diagnostic of diabetes.