Measurement of Carbonic Anhydrase I and II Isozymes in Feces as a Marker of Occult Blood in Horses with Intestinal Tract Bleeding

Although endoscopy is the definitive diagnostic method for the detection of colonic ulcers, the equipment required for performing the test is costly and difficult to use. Therefore, a simple cost-effective and reliable screening test for intestinal tract bleeding is needed. To this end, we measured carbonic anhydrase isozymes (CA-I and CA-II) originating from erythrocytes by ELISA in order to determine if they could be used as markers of occult blood in feces. For fecal extract preparation, 2 g of feces were mixed with 4 ml of 0.01 M Tris-HCl (pH 8.0) containing 0.01% thimerosal. The concentrations of CA-I and CA-II in the fecal samples of 13 clinically normal racehorses were found to be 30.0 ± 10.0 and 34.0 ± 13.0 ng/ml, respectively. Increased concentrations of CA-I were detected in the fecal samples of 5 horses after blood administration; however, no increase was observed in CA-II. The concentrations of CA-I and CA-II in the fecal samples of 88 racehorses with clinical signs of equine gastric ulcer syndrome (EGUS) were 115.3 ± 79.0 and 41.0 ± 42.0 ng/ml, respectively. Thus, our results indicate that CA isozymes can be useful as markers of occult blood in the fecal samples of horses with intestinal tract bleeding.