Review Question - QID 104294

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Renal Tubular Acidosis (RTA) Introduction Renal Tubular Acidosis Type Etiology Pathogenesis Treatment Comments Type II (proximal) Fanconi syndrome Carbonic anhydrase II deficiency Medications acetazolamide ifosfamide topiramate Heavy metals e.g., mercury, cadmium, copper, and QID: 104294 (M2.RL.15.20)

QID 104294 (Type "104294" in App Search)

A 64-year-old man presents to his primary care physician's office for a routine check-up. His past medical history is significant for type 2 diabetes mellitus, hypertension, chronic atrial fibrillation, and ischemic cardiomyopathy. On his last visit three months ago, he was found to have hyperkalemia, at which time lisinopril and spironolactone were removed from his medication regimen. Currently, his medications include coumadin, aspirin, metformin, glyburide, metoprolol, furosemide, and amlodipine. His T is 37 C (98.6 F), BP 154/92 mm Hg, HR 80/min, and RR 16/min. His physical exam is notable for elevated jugular venous pressure, an S3 heart sound, and 1+ pitting pedal edema. His repeat lab work at the current visit is as follows:

Sodium: 138 mEq/L, potassium: 5.7 mEq/L, chloride 112 mEq/L, bicarbonate 18 mEq/L, BUN 29 mg/dL, and creatinine 2.1 mg/dL.

Which of the following is the most likely cause of this patient's acid-base and electrolyte abnormalities?

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Furosemide

4/49

Chronic renal failure

39%

19/49

Glyburide

2/49

Renal tubular acidosis

45%

22/49

Amlodipine

0/49

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This diabetic with a non-anion gap metabolic acidosis (AG = 138-(112+18)=8, normal 6-12), hyperkalemia, and renal insufficiency should be suspected of having type 4 renal tubular acidosis (RTA).

Type 4 RTA is caused by either a deficiency of aldosterone or decreased sensitivity of the renal tubules to aldosterone. The lack of effect of aldosterone leads to decreased secretion of acid as ammonium (NH4+) and retention of potassium. Type 4 RTA may occur in the setting of diabetic nephropathy and can be exacerbated by drugs that inhibit the renin-angiotensin-aldosterone system, such as ACE inhibitors or ARBs.

Illustration A summarizes the characteristics of the different types of RTA. Illustration B lists a number of medications associated with RTA.

Incorrect Answers:
Answer 1: Furosemide is a loop diuretic that may cause contraction alkalosis due to hypovolemia, which would cause a primary increase in bicarbonate.
Answer 2: Chronic renal failure can cause anion-gap metabolic acidosis due to failure to excrete acid as NH4+.
Answer 3: Glyburide is a sulfonylurea hypoglycemic drug that can cause hypoglycemia, but is not associated with acid-base disturbances.
Answer 5: Amlodipine is a calcium channel blocker that is not associated with acid-base disturbances.

ILLUSTRATIONS: