Electrolyte Disorders USMLE Step 1 Practice Question
A 68-year-old man with stage 3 CKD and type 2 diabetes presents with polyuria and polydipsia. Vital signs: BP 158/92, HR 104, RR 22, temp 37.2°C, SpO2 98%. Serum sodium 152 mEq/L, glucose 580 mg/dL, osmolality 330 mOsm/kg, creatinine 2.1 mg/dL. Urine osmolality is 250 mOsm/kg with negative ketones. He denies recent medication changes. Which mechanism best explains his polyuria?
Answer choices
- APrimary polydipsia
- BOsmotic diuresis from hyperglycemiaCorrect answer
- CDiabetes insipidus secondary to hyperglycemia
- DNephrogenic diabetes insipidus from chronic kidney disease
- ESIADH with secondary hyperglycemia
- FF. Acute tubular necrosis from diabetic ketoacidosis
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.