Effect of in vitro gastrointestinal environment on immunochemical fecal occult blood test

Abstract

Objective To investigate the effect of gastrointestinal environment on fecal occult blood test. Methods Mixed peripheral venous blood (45 ml) of 25 healthy volunteers from medical examination center of China-Japan Friendship Hospital in 2015 were collected to establish an in vitro gastrointestinal digestion model. The model was used to study the effects of different digestion time and concentration of digestive juice on the immunochemical fecal occult blood test using two kinds of occult blood detection reagents. Results When the amount of bleeding was over 5 ml, fecal occult blood test still showed positive after artificial stomach liquid digestion for 2 hours and artificial intestinal liquid digestion for 5 hours.The fecal occult blood test turned negative after artificial stomach liquid digestion for 0.5-3 hours and artificial intestinal liquid digestion for 3 hours. The positive rate of fecal occult blood test was closely related to the amount of bleeding. When the amount of bleeding was large and bleeding was acute, false negative could be caused by postzone phenomenon. The upper detection limit of two reagents was more than 3 165 ng/L, and the lower detection limit was0.2 ng/L. Conclusions Higher positive rate was detected not only in lower digestive tract bleeding but also in upper gastrointestinal bleeding with immunoassay method. Immunochemical fecal occult blood reagent had a wide detection range and could meet the clinical requirements for detection of gastrointestinal bleeding. (Chin J Lab Med, 2017, 40: 294-297) Key words: Occult blood; Feces; Gastrointestinal tract; Hemoglobins