A stool specimen that appears black and tarry should be tested for the presence of:

• A. Occult blood
• B. Fecal fat
• C. Trypsin
• D. Excess mucus

Answer: (A)

A stool that is black and tarry points to digested blood in the GI tract, so the test of choice is to look for occult blood in the stool. Occult blood testing detects trace amounts of heme in the stool, confirming the presence of blood even when it isn’t visibly obvious. The black, tarry appearance (melena) specifically arises from blood that has been exposed to stomach acid and digested as it moves through the gut, making occult blood testing the most direct way to assess for GI bleeding.

Fecal fat testing would be used to evaluate fat malabsorption, not bleeding. Trypsin testing assesses pancreatic enzyme activity, not blood in stool. Excess mucus points to inflammatory or mucous changes in the intestinal lining, not blood detection.