Hematuria and false-positive tests for stool occult blood

A false-positive test for occult blood may result when stool samples are collected from a toilet bowl contaminated with urine that contains blood. This was the case in three patients subjected to extensive work-up for gastrointestinal bleeding. In vitro tests confirmed this reaction. Hematuria may not be noted by the patient, or it may be masked by colored toilet bowl cleaners when samples for test cards are collected at home.