In acute diarrhea, sodium is typically:

• A. High
• B. Low
• C. Normal
• D. Varied

Answer: (B)

Acute diarrhea causes a rapid loss of fluid and electrolytes in the stool, which lowers the effective circulating blood volume. In response, the body activates mechanisms to conserve volume, notably the renin-angiotensin-aldosterone system, which increases sodium reabsorption in the kidneys. This heightened reabsorption decreases the amount of sodium excreted in urine, so urinary sodium is typically low during diarrheal dehydration. Keep in mind that serum sodium can vary depending on how fluids and electrolytes are replaced and the overall hydration status, but the typical finding in the context of volume depletion from acute diarrhea is a low urinary sodium.