USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

Which condition may lead to metabolic alkalosis due to volume contraction?

1. Hypothyroidism

2. Chronic diarrhea

3. Heart failure

4. Asthma

The correct answer is: Chronic diarrhea

The condition that can lead to metabolic alkalosis due to volume contraction is chronic diarrhea. In chronic diarrhea, the loss of gastrointestinal fluids can lead to the depletion of bicarbonate and volume contraction, which can paradoxically result in an increase in serum bicarbonate concentration, thus causing metabolic alkalosis. When the body is volume-contracted, there is a compensatory response that can affect renal function and electrolyte balance, leading to the retention of bicarbonate or an increase in its production. This shift can manifest as metabolic alkalosis, especially in scenarios where there is significant extracellular fluid loss and subsequent renal compensation. Other conditions listed—such as hypothyroidism, heart failure, and asthma—do not typically cause metabolic alkalosis due to volume contraction in the same way that chronic diarrhea does. Hypothyroidism may lead to a variety of metabolic disturbances, but it is not primarily associated with volume contraction-induced metabolic alkalosis. Heart failure can contribute to fluid overload, leading more commonly to metabolic acidosis rather than alkalosis. Asthma is characterized by bronchoconstriction and airway inflammation, which can lead to respiratory acidosis rather than metabolic alkalosis. Thus, chronic diarrhea stands out as the condition that specifically leads to metabolic alkalosis through the mechanism of volume contraction