In a dehydrated patient with diarrhea and absent deep tendon reflexes, which electrolyte abnormality is most likely?

• A. Hypercalcemia
• B. Hyponatremia
• C. Hyperkalemia
• D. Hypokalemia

Answer: (D)

Potassium loss in the GI tract drives this picture. Diarrhea washes potassium out of the body, and in dehydration you end up with hypokalemia. Low potassium makes nerve and muscle cells less excitable, so muscles weaken and reflexes diminish or disappear. This matches the patient’s presentation of weakness with absent deep tendon reflexes. Other disturbances don’t fit as neatly: hypercalcemia isn’t typically caused by diarrhea and wouldn’t explain the acute GI-related potassium loss; hyponatremia can cause confusion or seizures but doesn’t specifically produce the reflex-suppressing weakness seen here; hyperkalemia would cause weakness too, but in the setting of diarrhea you’re more likely to see potassium depletion from stool losses rather than retention.