Hemoccult detection of fecal occult blood quantitated by radioassay.

Results from the quaiac slide or Hemoccult (HO) test for fecal occult blood were compared with quantitative determinations of gastrointestinal loss after intravenous administration of 51Cr-labeled red cells. Subjects were 80 consecutive patients, without dietary restriction, who were referred because of clinical suspicion of gastrointestinal blood loss or complex anemia. A total of 555 stool specimens analyzed for 51Cr loss were graded negative, trace, or positive by the HO method. Of 338 specimens containing 0-2 ml/day by isotope assay, 7.4% were positive to the HO qualitative test. Loss of at least 10 ml/day in 51Cr equivalent was necessary to assure that the majority of HO reactions would be positive. Of specimens containing more than 30 ml/day, 93% were positive. The ratio of 51Cr-labeled red cell equivalents to stool volume and the percentage of positive HO reactions increased together. When this ratio exceeded 10%, two thirds of the HO responses were positive.