In suspected fat malabsorption, which stool test is most sensitive for detecting fat malabsorption when the patient consumes a fat-containing diet?

• A. Stool for leukocytes
• B. Stool for 72-hour fecal fat
• C. Stool for ova and parasites
• D. Stool for culture and sensitivity

Answer: (B)

When evaluating suspected fat malabsorption, quantifying how much fat leaves the body while fat intake is adequate is key. The 72-hour fecal fat collection is the most sensitive test for this because it measures total fat excreted over several days of a fat-containing diet. By collecting all stool for 72 hours and analyzing the fat content, you capture the ongoing loss that can vary day to day, making it more reliable for detecting malabsorption than a single stool sample. If the fat excretion is above normal (a commonly used threshold is around 7 g/day, though lab references vary), fat malabsorption is indicated.

The other stool tests are aimed at different problems: stool leukocytes suggest inflammatory processes in the gut, ova and parasites look for parasitic infections, and culture and sensitivity identifies bacterial pathogens. None of these specifically assess fat absorption, especially under a fat-containing diet, which is why the 72-hour fecal fat test is the best choice for detecting fat malabsorption.