Thromboelastographic evaluation of haemostatic abnormalities in uncomplicated canine babesiosis

Abstract

Babesiosis, caused by Babesia rossi, is a common cause of morbidity and mortality of dogs in South Africa. Canine babesiosis can be classified either as uncomplicated or complicated based on the degree of anaemia and the severity of the presenting clinical signs.1,2 In uncomplicated babesiosis, the clinical signs are mostly attributable to the degree of the anaemia, whereas in complicated babesiosis the disease process is characterised by additional organ involvement.3,4 One of the most common haematological hallmarks of canine babesiosis, caused by B. rossi, is thrombocytopenia, which is not associated with clinical haemorrhage despite very low platelet counts that would normally cause inability to maintain normal primary haemostatic function.5 The aim of this study was to describe the thromboelastographic findings in uncomplicated canine babesiosis and compare them with those of normal, healthy control dogs. We hypothesised that these dogs would have a normal to hypercoagulable haemostatic capacity, despite the severe thrombocytopenia, and that this could be detected with thromboelastography (TEG), which has previously been shown to correlate well with clinical signs of haemorrhage in dogs.6 This was a prospective, cross sectional, observational study that included 20 client-owned dogs, diagnosed with uncomplicated canine babesiosis at the Onderstepoort Veterinary Academic Hospital (OVAH). Infection with B. rossi was confirmed by polymerase chain reaction (PCR) and reverse line blot (RLB) hybridisation assay. Blood samples were collected at the time of diagnosis. A group of 10 healthy control dogs were included for comparison. Antithrombin activity (AT) was measured using an automated spectrophotometric analyser (Cobas Integra 400, Roche, South Africa). D-dimer was measured using an immunometric flow-through principle (D-dimer Single test, Nycocard Reader II, Medinor A/S). Prothrombin time (PT), activated partial thromboplastin time (aPTT) and fibrinogen assays were performed on the ST art® 4 analyser (Diagnostica Stago, Roche, South Africa). TEG analysis was performed using the TEG® 5000 Thromboelastograph® Haemostasis System (Haemoscope, Pro-Gen Diagnostics (Pty) Ltd, South Africa). A complete blood count was performed on the ADVIA 2120 (Siemens, South Africa). The results of the babesiosis and control groups were compared using the Mann-Whitney U test or the Students t-test based on normality. The normality assumption for distribution of the variables in the data was evaluated using the Shapiro-Wilk test. The statistical significance was set at p<0.01. The mean haematocrit (Ht) and median platelet count was significantly lower in the babesiosis group than the controls (0.29 vs. 0.50 L/L; p<0.01 and 22.0 vs. 374.5 x 109/l; p<0.01, respectively). There was no significant difference in any of the TEG parameters between the babesiosis group and the controls. The medians for the various TEG parameters in the babesiosis group versus the controls were; R: 5.5 vs. 4.4 min (p=0.05); K: 2.5 vs. 2.0 min (p=0.08); angle: 58.3 vs. 61.1 degrees (p=0.35); MA: 47.0 vs. 57.0 mm (p=0.02); G: 4.9 vs. 6.7 dyn/cm2 (p=0.02); LY30: 0.00 vs. 0.6% (p=0.20); and LY60: 0.00 vs. 3.0% (p=0.014). The median fibrinogen concentration was significantly higher in the babesiosis group than in the control group; 5.8 g/L (5.0 – 7.0) vs. 2.9 g/L (2.5 – 3.3); (p<0.01). The mean AT activity was significantly lower in the babesiosis group than in the control group; 102.6 mg/dl (89.9 – 112.8) vs. 127.8 mg/dl (110.6 – 134.8); (p<0.01). The median D-dimer concentration was not significantly different in the babesiosis group compared to the control group; 0.3 mg/L (0.1 – 0.4) vs. 0.1 mg/L (0.1 – 0.2); (p=0.016). Median PT was not significantly different in the babesiosis group compared to the control group; 6.5 sec (6.4 – 7.2) vs. 6.8 sec (6.6 – 7.5); (p=0.14). Median aPTT was significantly prolonged in the babesiosis group compared to the control group; 13.6 sec (12.4 – 14.5) vs. 11.5 sec (10.7 – 12.2); (p<0.01). Despite the severe thrombocytopenia, dogs suffering from uncomplicated babesiosis did not have clinical signs of haemorrhage. The thromboelastograms of the babesiosis group were normal to hypercoagulable and thus correlated well with the clinical phenotype. Copyright