Insensitivity of guaiac slide tests for detection of blood in gastric juice.

Two guaiac slide tests (Hemoccult and Fe-Cult) were evaluated for their ability to detect blood in gastric juice and other fluid mixtures relevant to clinical testing in upper gastrointestinal hemorrhage. Blood was added to these fluid mixtures in various amounts sufficient to yield concentrations from 20 microL blood/dL to 4000 microL/dL. With these agents we frequently could not detect blood in unbuffered gastric juice at concentrations as great as 4000 microL/dL. Buffering of gastric juice to pH 4 with either of two antacids only slightly restored sensitivity for blood detection. In contrast, blood in gastric juice obtained from subjects previously given intravenous cimetidine tested positive at concentrations as low as 50 microL/dL. The ability of both test agents to detect blood in gastric juice was considerably enhanced by neutralizing gastric juice with 0.1 N NaOH.