Endocrinology and Diabetes Mellitus
Diabetic emergencies
Diabetic ketoacidosis shows hyperglycaemia, ketonaemia and acidosis (pH <7.3, bicarbonate <15); hyperosmolar hyperglycaemic state shows glucose above 30 mmol/L, osmolality above 320 mOsm/kg and minimal ketosis, with higher mortality. Give fluids first, check potassium before insulin, and replace potassium once below 5.5 mmol/L; do not give routine bicarbonate. Watch for hypokalaemia, and for cerebral oedema in children.
Thyroid and adrenal disease
TSH is the first-line test. Primary hypothyroidism gives a high TSH with low free T4; subclinical disease gives a high TSH with normal free T4. Primary adrenal insufficiency shows low cortisol with high ACTH, hyponatraemia, hyperkalaemia and hyperpigmentation, and is confirmed by a short synacthen test; secondary disease has low ACTH and no pigmentation.
Calcium and bone
Correct calcium for albumin before interpreting it, and measure PTH: a high PTH with high calcium suggests primary hyperparathyroidism, while a suppressed PTH suggests malignancy. Treat hypercalcaemia with intravenous saline, then bisphosphonate. A DEXA T-score of −2.5 or below defines osteoporosis.
Traps: diagnosing hypothyroidism on free T4 alone in suspected pituitary disease (TSH is unreliable there); missing adrenal insufficiency in a patient whose hyponatraemia looks like SIADH; forgetting that hyponatraemia can be the presenting feature of hypothyroidism or adrenal disease and must be excluded before diagnosing SIADH.
Rule of thumb: corrected calcium (mmol/L) = measured calcium + 0.02 × (40 − albumin in g/L). For a patient with albumin 25 g/L and calcium 2.10 mmol/L, corrected calcium is 2.10 + 0.30 = 2.40 mmol/L - normal.