A new occult blood test not subject to false-negative results from reducing substances.

A new stool occult blood test is described with improved sensitivity (more true positives) and specificity (fewer false negatives; more true negatives) than other clinically available procedures. The procedure chemically separates heme from globin and extracts heme into ethyl acetate, where a colorimetric reaction gives semiquantitative estimation of hemoglobin. The test is based on the retention of heme pseudoperoxidase activity in the ethyl acetate. Specifically, peroxide is degraded by heme to superoxide radicals which oxidize a chromophore to a colored compound. Various diamino and other chromogens are evaluated, and a new reagent, the noncarcinogenic diamino compound TMB is recommended for routine use. False positives may account for two thirds of all positives in routine screening. In addition, special diets and time delays due to dietary restrictions are avoided in this test. The test is also inexpensive and easy to perform. A technologist can perform 30 or more tests per hour.