Experimental detection of canine haemoglobin (occult blood) in canine faeces by reversed passive latex agglutination.

A reversed passive latex agglutination test (RPLA) using anti-canine haemoglobin (Hb) antibody was developed for detecting bleeding in the lower digestive organs in dogs, and its applicability as a simple test for faecal occult blood was assessed. In Ouchterlony's gel immunodiffusion test, the anti-canine Hb antibody used to sensitize the latex reacted with canine Hb but not with Hbs, plasmas or meat extracts from pigs, goats, sheep, cattle, horses or chickens, or with fish extracts. Using latex sensitized with 50 micrograms/mg of anti-canine Hb IgG antibody, the lowest limit of detection for canine Hb was 21 micrograms/ml, and the latex reacted negatively with all test specimens other than canine Hb. In an in vitro experiment with a mixture of canine faeces and erythrocytes, the antigenicity of the Hb was found to undergo only very slight changes even when the specimens were allowed to stand for 12 h at room temperature. Hb could not be detected by RPLA in any of four successive faecal samples from three experimental dogs after infusion of autologous blood (5, 3 or 1 ml) into the stomach. In 3 other experimental dogs given an infusion of autologous blood (5, 3 or 1 ml) into the ascending colon, the presence of Hb was confirmed by RPLA in all four successive faecal samples obtained from those which received 5 or 3 ml of blood and in all except that obtained following the first defecation from the animal which had received 1 ml of blood.