Establishment of a fecal occult blood test method in detecting reducing substances of feces and its clinical application

Abstract

Objective To establish a method for detecting reducing substances,avoid false negative of fecal occult blood test and improve detection rate.Methods The detection limit of chemical method (ortho-tolidine) and immune colloidal gold method were measured by a series of distilled water diluted known concentration of Hb.As negative control with distilled water,study the impact of reducing substances on the chemical method and the immune colloidal gold method.Establish a method to detect reducing substances in feces and use for clinical fecal occult blood test.Results The detection limit of hemoglobin with the chemical method is≥4.9 mg/L,it is from1.2 mg/L to 2500 mg/L with the colloidal gold method.When vitamin C concentration of injections or tablets is≥156.3 mg/L,the chemical method had the false negative.When tartaric acid concentration is≥5000 mg/L or citrate concentration is ≥2500 mg/L,the colloidal gold can be false positive.Mixed the 0.1 g/L iodine solution and 1.0 g/L starch solution with equal volume,at the ordinary temperature and pH 6.6,detecting the reducing substances,which is the improved chemical method,there have no false negative result when the vitamin C concentration is＜1000 mg/L.In the 294 clinical specimens,56 were positive using the chemical method,106 were positive using the improved chemical method and 40 were positive using the colloidal gold method.Conclusions The improved chemical method can detect the reducing substances and eliminate its interference,avoid the false negative in fecal occult blood test. Key words: Fecal occur blood test; Reducing substances; Improved chemical method