Endocrinology, Diabetes, and Metabolism
Thyroid
Screen with TSH; free T4 and total T3 follow. Remember sick euthyroid physiology - abnormal thyroid tests in hospitalized patients often resolve. Thyroid storm is a clinical diagnosis (fever, tachyarrhythmia, CNS and GI dysfunction) treated with beta blockade, thionamide, iodine after the thionamide, and steroids. Use PTU in the first trimester. Myxedema coma requires IV levothyroxine plus stress-dose hydrocortisone until adrenal insufficiency is excluded.
Adrenal and calcium
In suspected adrenal crisis, draw a cortisol and give dexamethasone (which does not interfere with the cosyntropin stimulation test) plus isotonic fluids and glucose. Primary adrenal insufficiency causes hyperpigmentation, hyponatremia, hyperkalemia, and hypotension; secondary does not. For calcium disorders, correct the calcium for albumin (add 0.8 mg/dL per 1 g/dL that albumin is below 4). Primary hyperparathyroidism shows high or inappropriately normal PTH with high calcium and low phosphate; malignancy-associated hypercalcemia suppresses PTH.
Diabetes
Differentiate DKA (glucose often <250, ketones, anion gap acidosis) from HHS (very high glucose, hyperosmolality, minimal ketosis). In both, total-body potassium is depleted - check and replace potassium before insulin if it is below 3.3 mEq/L. A1c is unreliable in anemia, hemoglobinopathies, pregnancy, recent transfusion, and advanced CKD. Metformin is contraindicated below an eGFR of 30 and held for contrast or acute illness; SGLT2 inhibitors can cause euglycemic DKA. Estimated sodium in hyperglycemia = measured sodium + 1.6 mEq/L per 100 mg/dL glucose above 100.