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

Summary: False positive and negative hemoccult reactions on a normal diet and effect of diet restriction. M. L. Bassett and K. J. Goulston, Aust. N.Z. J. Med . 1980, 10 . pp. 1–4. The reliability of Hemoccult, a guaiacimpregnated slide for detecting faecal occult blood, was assessed on both normal and restricted diets. Two‐hundred‐and‐twenty‐five faecal samples 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. Faecal blood was quantitated by 51 Cr red cell labelling. On a normal diet, the false positive rate was 11%. This reduced to 2% on a high fibre diet free of red meat and raw fruit and vegetables. This false positive rate is lower than has been previously reported for other : more widely‐used, occult blood tests. The overall false negative rate was 48%; this diminished with increasing faecal blood loss.