Chronic Kidney Disease USMLE Step 1 Practice Question
A 46-year-old man with bipolar disorder presents with polyuria and polydipsia. He has taken lithium for 8 years. Vital signs show BP 138/82 mmHg, HR 88/min, RR 16/min, temp 37°C, SpO2 98%. Serum sodium is 149 mEq/L; serum creatinine 1.2 mg/dL. Urine osmolality remains 285 mOsm/kg despite water deprivation and minimal response to desmopressin. Urinalysis shows no proteinuria. Which mechanism best explains his presentation?
Answer choices
- ADeficient release of antidiuretic hormone from the posterior pituitary
- BImpaired response of collecting duct principal cells to antidiuretic hormoneCorrect answer
- CEnhanced aquaporin insertion into the collecting duct membrane
- DConstitutive activation of vasopressin V2 receptors
- EExcess secretion of aldosterone from the adrenal cortex
- FDecreased expression of aquaporin-2 water channels in the collecting duct epithelium
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