HemoQuant, A New Quantitative Assay for Fecal Hemoglobin

Abstract

HemoQuant, an assay [for use in humans] based on heme-derived porphyrin, quantifies both total fecal Hb and that fraction already converted to prophyrin by gut flora (the intestinal converted fraction). Recovery by HemoQuant of blood added to stools exceeded 99% and was not affected by ascorbic acid, Fe or other additives. HemoQuant was used to evaluate the performance of Hemoccult on 1018 stools. Hemoccult sensitivity differed widely, remaining negative with up to 42.5 mg Hb per gram of stool (about 43 ml/d of blood) but positive with only 0.04 mg of Hb per g of stool. Driest stools tended to be Hemoccult-negative and the wettest Hemoccult-positive. Hemoccult-negative stools became positive after aqueous dilution independent of Hb concentration. The intestinal converted fraction, not detected by guaiac tests, often constituted most of the fecal Hb equivalents and was significantly higher in Hemoccult-negative than in Hemoccult-positive stools. Hemoccult lost reactivity during fecal storage due to progressive heme degradation. Frequent false-negative and false-positive reactions of Hemoccult were explained largely by variations in stool liquidity and heme degradation.