Endocrinology, Diabetes, and Metabolism
Core concepts
Expect questions on diabetic ketoacidosis and hyperosmolar hyperglycemic state, thyroid disease, adrenal insufficiency, calcium and sodium disorders, pituitary disease, and outpatient diabetes pharmacology. In DKA, total body potassium is depleted even when serum potassium is normal or high; insulin is withheld until potassium is at least 3.3 mEq/L. HHS features profound hyperosmolality and minimal ketosis. Thyroid storm is clinical, treated with thionamide, iodine, beta-blocker, and steroids. Primary adrenal insufficiency causes hyponatremia, hyperkalemia, and hypotension; confirm with cosyntropin stimulation.
Traps
- Giving insulin in DKA before correcting severe hypokalemia.
- Using only corrected calcium without checking albumin or ionized calcium in critically ill patients.
- Missing euglycemic DKA in a patient on an SGLT2 inhibitor.
- Treating subclinical hypothyroidism aggressively without symptoms.
- Confusing primary hyperaldosteronism (hypertension plus hypokalemia) with secondary causes.
- Forgetting that metformin should be held with contrast or severe illness due to lactic acidosis risk.
Worked example
A 24-year-old with type 1 diabetes presents with vomiting, glucose 480 mg/dL, pH 7.12, bicarbonate 8, and potassium 3.1. The error is starting an insulin infusion immediately. Give isotonic fluids and potassium first; once potassium is above 3.3, begin insulin. The anion gap closes as ketones clear, and bicarbonate is rarely needed. Rule of thumb: in DKA, fix the potassium before you fix the sugar.