False Positive and Negative Hemoccult Reactions on a Normal Diet and Effect of Diet Restriction

Abstract

The reliability of Hemoccult, a guaiac-impregnated slide for detecting fecal occult blood, was assessed on normal and restricted diets. Fecal samples (225) were obtained from 40 patients on a normal diet and 115 samples from 20 patients on a restricted diet. A single Hemoccult I test was performed on each sample. Fecal blood was quantitiated by 51Cr red cell labeling. On a normal diet the false-positive rate was 11%. This reduced to 2% on a high fiber diet free of red meat and raw fruit and vegetables. This false-positive rate is lower than previously reported for other more widely-used, occult blood tests. The overall false-negative rate was 48%; this diminished with increasing fecal blood loss.