Fodrets inverkan på resultatet vid undersökning av förekomst av ockult blod i avföringen hos hund

Abstract: Hemoplus® (Sarstedt, Nümbrecht, Tyskland) is a guaiac-based fecal occult blood test developed for human medicine. Guaiac-based tests make use of the pseudoperoxidase activity of hemoglobin so the test is not specific for human hemoglobin and can therefore be used in veterinary medicine. Peroxidase-containing foods such as meat (hemoglobin and myoglobin) can cause false-positive results of the test. To ensure that a positive result is not caused by diet, it has been suggested that canine patients should be fed a meatless diet for a few days prior to fecal occult blood testing. The aim of this study was to evaluate the effect of commercial dog food on guaiac-based tests. In this study fecal samples from healthy dogs were analyzed with Hemoplus®. The dogs were either fed only dry food diet for four days or a dry food mixed with canned food for three days prior to testing. Three other dogs were fed raw minced meat or black-pudding for two days. Fecal samples were allowed to dry after they had been applied to the Hemoplus-test. All samples were analyzed according to the Hemoplus® test-instructions by adding only the reagent and all samples, except samples of 23 dogs fed the dry food diet, were analyzed by adding water to the samples before the reagent was added. Wetting the feces with water (rehydrating) increases the sensitivity of guaiac-based tests but reduces specificity. All but one fecal samples from dogs fed minced meat or black-pudding were positive both rehydrated and non-rehydrated. One sample was positive only when rehydrated. When hemolysed blood was mixed with feces, a positive result was obtained only when the sample had been rehydrated. All 43 samples from dogs fed the dry food diet were negative. Different types of dry food diets have been used in the study, the majority having chicken as protein-source. Two different types of canned food have been used. One of them, containing beef and liver, resulted in samples from all 16 dogs being negative upon analyzing. The other, containing lamb and rice, resulted in all 16 samples but one being negative when non-rehydrated prior to analyzing them but positive when rehydrated. Different protein-sources or differences in processing the diets may explain the varying results between the diets. To reduce the risk of having false-negative results, we recommend that samples from patients should be analyzed both rehydrated and non-rehydrated. This study suggests that feeding only dry food diet for four days prior to the test is sufficient to reduce the risk of false-positive results. Additional studies on dogs are required to evaluate the sensitivity and specificity of the Hemoplus-test for dogs feces. One should evaluate dry food diets with other protein-sources than chicken.