Association of increased erythrocyte osmotic resistance with haematological and histopathological findings in dogs with a congenital extrahepatic portosystemic shunt

The aim of the study was to investigate changes in erythrocyte osmotic resistance in relation to haematological and histological changes in dogs with a congenital portosystemic shunt. Osmotic fragility tests with complete blood counts and liver histological examinations were performed in 12 dogs with single extrahepatic portosystemic shunt confirmed by surgical exploration. Laboratory results were compared with those from 30 healthy dogs. Dogs with portosystemic shunt had a significantly increased erythrocyte osmotic resistance (P < 0.01) with 5%, 50% and 90% haemolysis corresponding to 0.45%, 0.35% and 0.30% NaCl solution, respectively. Statistical analyses revealed no correlation between haematological indicators and the osmotic fragility test results. Increased osmotic resistance was significantly associated with hepatic lipogranulomas. Based on these results, dogs with a congenital portosystemic shunt have a significantly increased erythrocyte osmotic resistance suggesting impaired red blood cell deformability. Osmotic resistance test that until now was not studied in canine hepatopathies seems to be independent of routinely performed haematological tests. Portosystemic vascular anomaly, osmotic fragility, liver biopsy, canine Portosystemic shunt (PSS) is the most common vascular anomaly in dogs. Persistent communication in single PSS allows blood to bypass the liver and be delivered directly from the portal bloodstream into systemic circulation. All laboratory abnormalities are related to secondary metabolic changes due to progressive liver atrophy (Mathews and Bunch 2005). In human medicine, chronic liver diseases are associated with increased erythrocyte osmotic resistance (OR) due to accumulation of membrane cholesterol as a result of impaired lipid metabolism. This change in membrane composition with an increased surface area to volume ratio morphologically corresponding to target cells, has a direct effect on red blood cell deformability (Vassiliadis et al. 2010). Target cells are commonly also seen in dogs with chronic liver disorders, but the alterations in erythrocyte OR in hepatopathies have not been described, yet. A similar tendency for increased erythrocyte osmotic resistance in a portosystemic shunt could suggest a similar pathogenesis to impaired erythrocyte deformability in humans with chronic liver disease. Liver biopsy is the gold standard in the diagnostics of hepatic disorders. The aim of this study was to investigate changes in erythrocyte osmotic resistance in dogs with a single extrahepatic portosystemic shunt, and to determine associations with alterations in the haematology profile and liver histopathological findings. ACTA VET. BRNO 2013, 82: 393–398; doi:10.2754/avb201382040393 Address for correspondence: MVDr. Kristína Řeháková, Small Animal Clinical Laboratory Faculty of Veterinary Medicine University of Veterinary and Pharmaceutical Sciences Brno Palackého tř. 1/3, 612 42 Brno, Czech Republic Phone: +420 541 562 227 E-mail: [email protected] http://actavet.vfu.cz/ Materials and Methods Animals Twelve dogs with a history consistent with the diagnosis of portosystemic shunt confirmed by surgical exploration were used in this study. Yorkshire Terrier, accounting for 7 cases, was the most common breed identified in the study. Other breeds included one each of the following: Bichon Frise, Toy Poodle, West Highland White Terrier, Cairn Terrier and a mixed-breed dog. The median age and median body weight of the dogs with a portosystemic shunt was 13 months (range 3 to 28 months) and 2.2 kg (range 1.5 to 8.5 kg), respectively. Seven animals were males, five were females. The control group consisted of 30 privately owned healthy dogs. Haematological examination In all dogs, the peripheral blood for laboratory analysis was collected from the jugular vein. Quantitative haematological examination (Analyser Celltac alpha MEK 6318, Nihon Kohden, Japan) with a blood smear preparation was performed from blood collected to ethylenediaminetetraacetic acid (EDTA) (Tapval, Dispolab, Czech Republic). Haematological examination included red blood cell (RBC) count, haematocrit (Ht) value, haemoglobin (Hb) concentration, mean cell volume (MCV), mean cell haemoglobin (MCH), mean cell haemoglobin concentration (MCHC), white blood cell (WBC) count and platelet count determination. The presence of target cells was proved by microscopic examination of the blood smear. Osmotic fragility test The blood samples for osmotic fragility test (OFT) were collected on lithium-heparin (Tapval, Dispolab, Czech Republic) a suitable anticoagulant for hypotonic red blood cell lysis (Sláma et al. 2006). The OFT was performed according to the method of Dacie and Lewis (Comazzi et al. 2002) by adding 25 μl of blood into a 2.5 ml NaCl solution of decreasing concentrations of 0.90– 0.10%. After 30 min of incubation at room temperature and centrifugation (165 g, 10 min), the supernatant absorbance was measured at 540 nm (ELISA reader ELX 808 BioTek Instruments Inc., USA). Supernatant from saline was used as a negative control without provoking haemolysis; supernatant from 0.1% NaCl solution served as positive control with complete haemolysis. Histological examination Liver biopsy samples were obtained from 10 dogs with PSS during surgical shunt attenuation. Samples were routinely stained with haematoxylin-eosin and evaluated using an individual score system for portal area changes and for parenchymal changes (Simpson et al. 1997; Isobe et al. 2008; Lee et al. 2011). In the portal area, absence of portal vein (0-3), arteriolar proliferation (0-3), biliary hyperplasia (0-2) and portal fibrosis (0 or 1) were scored. In the parenchyma, steatosis (0-3), lipogranulomas (0-3), pigment accumulation (0-2), inflammation (0 or 1) and necrosis (0 or 1) were evaluated. Statistical analysis Haematological results were reported as median values. A cumulative curve of haemolysis was drawn from the mean values for both PSS and control group. The mean concentrations of NaCl solution corresponding to the minimum (less than 5% haemolysis), medium (50% haemolysis) and maximum (more than 90% haemolysis) osmotic fragility were calculated. Mann-Whitney test was used to compare haematological data, Student’s t-test for changes in OFT. The level of significance was set at P < 0.05. Pearson’s correlation coefficient was used for correlation analyses between osmotic fragility and the haematocrit, haemoglobin, MCV, MCH and MCHC values. The association between abnormalities in OR and histological findings in the PSS group was evaluated using general linear modelling (GLM) (Statistica 6.0, Statsoft Inc., USA).