Evaluation of Russell's viper venom time as a test of coagulation in red-tailed hawks (Buteo jamaicensis)

Free-ranging red-tailed hawks (Buteo jamaicensis) risk coagulopathy due to frequent exposure to anticoagulant rodenticides by ingestion of intoxicated prey. Standardized tests to diagnose coagulopathies in birds are lacking... [ view full abstract ]

Free-ranging red-tailed hawks (Buteo jamaicensis) risk coagulopathy due to frequent exposure to anticoagulant rodenticides by ingestion of intoxicated prey. Standardized tests to diagnose coagulopathies in birds are lacking because differences between mammalian and avian coagulation limit the utility of commercial assays. Prothrombin time (PT) assays optimized with avian thromboplastin reagents have been used in research, but these reagents are difficult to prepare and reference ranges have not been developed for red-tailed hawks. We therefore evaluated the Russell's viper venom time (RVVT), a test of coagulation that uses a commercial reagent in red-tailed hawks. We hypothesized that RVVT would show strong correlation with PT in both healthy and sick or injured red-tailed hawks. Between May 2015 and February 2016, citrated plasma samples were collected from free-ranging, sick or injured hawks (n=13) and captive, clinically healthy hawks (n=10) for PT, RVVT, and fibrinogen assessment. For healthy hawks, the median PT=35.6 seconds (range=34.2 - 37.2) and the median RVVT=29.7 seconds (range=26.2 - 38.8). For sick hawks the median PT=35.6 seconds (range=31.7 - 38.1) and the median RVVT =31.1 seconds (range=24.2 - 39.8). We found no significant difference (Wilcoxon rank sum test) between healthy and sick hawks in either PT (p=0.57) or RVVT (p = 0.36). For all birds (n=23), the PT and RVVT were significantly correlated (Spearman’s r=0.428, p=0.04). Our results suggest that RVVT may be applicable for assessing coagulation in red-tail hawks. A larger sample size is needed to fully evaluate the correlation between PT and RVVT across a range of values.