Pesquisa de sangue oculto fecal em cães com hipercortisolismo pituitário-dependente

Abstract

In the small animal clinical practice, endocrine diseases are a subject of attention. The overexposure of endogenous cortisol, called hypercortisolism, is the third most diagnosed endocrinopathy. This thesis is divided in three chapters, the first refers to general considerations about hypercortisolism and the damaging effects of serum cortisol, its action in gastrointestinal system and the diagnostic method of fecal occult blood test (FOBT) as an early screening for tissue damage in gut mucosa. The second chapter aimed to investigate and to compare the analytical sensitivity of FOBT detection tests based on guaiac and benzidine reagents for the identification of blood in faecal samples obtained from healthy dogs. Those feces were forged with known amounts of the animal's own blood (hemoglobin/g faeces). Hemoglobin was added at 1, 5, 10, 20, 40 µg/g of feces and tested by both methods aforementioned. Three pathologists performed the reading of the photographed samples in a double-blinded manner. The analysis of the results showed that gFOBT had greater sensitivity, positive and negative predictive values, positive and negative likehood ratios and accuracy. The third chapter aimed to investigate the presence of FOBT by the guaiac method in dogs with pituitary-dependent hypercortisolism (HCPD) randomized in two groups: hypercortisolemic dogs (recently diagnosed, pharmacologically uncontrolled - positive control) and normocortisolemic (pharmacologically controlled, negative control). The results were also interpreted by three evaluators (double-blindly ) and analyzed according to different scenarios aiming to verify whether there is presence of FOB in dogs with spontaneous hypercortisolism or not [scenario 1, 0=0 (absence of FOB) and scores 1, 2, 3=1 (presence of FOB)]. This method aimed to reduce a possible effect of the high sensitivity of gFOBT for minimum amounts of hemoglobin within faecal samples (<1mg Hb/g faeces) observed in a pilot study (Chapter 2), or even to reduce the individual variability in the classification of the score 1 [scenario 2, scores 0 and 1=0 (absence of FOB) and scores 2 and 3=1 (presence of FOB)] . Additionally, the method applied was able to verify the applicability of the originally proposed scores in which 0 represents "absence" of FOB and scores 1, 2 and 3 as weakly, moderately, and strongly positive for FOB (scenario 3). It was observed that, despite all the proposed scenarios, there was a certain degree of agreement between the evaluators, however they were not strong at any moment, which raised questions about the variability of the colorimetric results obtained. It was not possible to state that hypercortisolism itself is related to occult fecal bleeding in dogs with HCPD (scenarios 1 and 3) as the high sensitivity of the gFOBT was suggested (scenario 2) and the slightest positive score was reclassified as being negative. The proportion of animals with no FOB (negative score) was significantly higher than the those with FOB (positive score) in both hypercortisolemic and normocortisolemic HCPD dogs (p=0.001690 and p=0.004343, respectively), indicating the absence of FOB in dogs with HCPD. Thus, in the light of the results obtained in this research, it is not possible to declare that there is occult fecal bleeding by the guaiac method in dogs with pituitary-dependent hypercortisolism, whether they are hypercortisolemic or not.