Step 1 Question of the Week: Renal Physiology

This week’s edition of the Step 1 Question of the Week comes from the area of renal physiology.  See if you can answer the question and then watch the video to learn the correct answer as well as the rationales for all of the options.

Renal Physiology

A 66-year-old man with a 15-year history of type 2 diabetes mellitus presents to his primary care physician for a routine evaluation. On that visit, his serum creatinine concentration is 2.2 mg/dL, which is elevated from his baseline concentration of 1.3 mg/dL determined 3 years prior. His physician prescribes an angiotensin-converting enzyme (ACE) inhibitor. However, at the follow-up visit, there is no improvement in his creatinine level or urinalysis results. In between visits, he is hospitalized for a mild acute asthma exacerbation and has an arterial blood gas determined, which shows an arterial blood pH of 7.33 and PCO2 of 40 mm Hg.

Other selected laboratory test results are:

Potassium: 5.5 mEq/L
Urine pH: 5.2
Sodium: 140 mEq/L
Bicarbonate: 18 mEq/L
Chloride: 110 mEq/L

Which of the following is the most likely diagnosis?

A. Acute kidney injury

B. Hyperreninemic hyperaldosteronism

C. Type I renal tubular acidosis

D. Type II renal tubular acidosis

E. Type IV renal tubular acidosis

We invite you to leave a comment with your answer as well as your rationale.  When you’re ready to check your work, watch the video!
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