Nitrosonapthol test for screening of small intestinal diarrheal disease in the dog

The nitrosonapthol test, which qualitatively measures urinary excretion of 4-hydroxyphenylacetic acid and related compounds, was evaluated as a screening test for small intestinal disease in 60 dogs with chronic diarrhea. Test results were positive in 8 of 13 dogs with pancreatic exocrine insufficiency, in 8 of 12 dogs with small intestinal malabsorption, in 2 of 17 dogs with colitis, and in all of 14 dogs with normal gut function and in which the specific cause of diarrhea was not determined. Test results were negative in 4 dogs with functional (stress-induced) diarrhea and in 25 clinically normal dogs. Thus, the test results were positive in 30 of 39 (77%) dogs with confirmed small intestinal or pancreatic disease or in which small intestinal disease was the most likely diagnosis, and in only 2 of 21 (9.5%) dogs with large intestinal disease (P less than 0.001). In human medicine, positive test results have been associated with bacterial overgrowth in the small intestine. Accordingly, antibiotics were administered orally to 8 of the dogs with diarrhea of undetermined cause. In all treated dogs, antibiotic therapy resulted in improvement in fecal consistency, decreased frequency of defecation, and a change from a positive to a less strongly positive or negative reaction to the nitrosonapthol test. These findings suggested that the nitrosonapthol test is useful in the discrimination of small intestinal from large intestinal diarrhea and as a guide to the use of oral antibiotic therapy in dogs with chronic diarrhea of undetermined cause.