Laboratory diagnosis of gastrointestinal bleeding.

The value of four tests to detect occult alimentary blood loss has been compared in normal subjects, in patients with and without alimentary disease, and in patients with congestive heart failure, and the sensitivities of these tests have been compared using suspensions of blood alone and blood in faeces. The Occultest proved almost as sensitive as did the benzidine test in the detection of faecal blood loss, and, if combined with a spectroscopic test for protoporphyrin, minimizes the number of ;false' positive results that are reported. Such false positive results will inevitably occur but are reduced by dietary restriction before the test is made.