Sensitivity and specificity of 20-minute whole blood clotting test, prothrombin time, activated partial thromboplastin time tests in diagnosis of defibrination following Malayan pit viper envenoming.

Malayan pit vipers (Calloselasma rhodostoma) are major health hazard in Southern Thailand causing systemic bleeding by defibrination and thrombocytopenia. Twenty minute whole blood clotting test (20WBCT) is a useful and informative bedside test recommended by WHO for diagnosis of significant coagulopathy following snakebite envenoming since it to some extent predicts the need for anti-venom therapy. Prothrombin time (PT), international normalized ratio (INR) and activated partial thromboplastin time (APTT) are standard clotting assays that are widely used for diagnosis of coagulopathy. The purpose of this study is to compare 20WBCT with the standard clotting assays (PT, INR, APTT, fibrinogen) in management of Malayan pit viper bitten-patients. We studied 296 victims prospectively during a 3-year period. In total, 115 (38.9%) cases showed a positive 20WBCT (un-clot) suggesting systemic envenomation. Thrombocytopenia (platelet count less than 100,000/μL), prolonged PT, prolonged APTT, INR ≥ 1.2, and fibrinogen level <100 mg/dl were found in 12.2%, 47.6%, 18.9%, 34.8% and 40.9%, respectively. Significant predictors for thrombocytopenia by multivariate analysis included systemic bleeding (p < 0.001), higher INR (p < 0.001), 20WBCT showing unclotted blood (p = 0.049), and longer bite-to-hospital time (p = 0.031). When a fibrinogen level below 100 mg/dl was determined as hypofibrinogenemic condition, INR had the highest area under ROC curve followed by 20WBCT and APTT, respectively, to identify such as hypofibrinogenemic condition. The diagnostic accuracy of 20WBCT and INR at or more than 1.155 were better than APTT at any cut-off points. INR >1.155 had a sensitivity of 78.5% and specificity of 90.3% while 20WBCT had sensitivity of 81.0% and specificity of 90.3%.
CONCLUSIONS: Both 20WBCT and INR are useful to assess coagulation abnormality in Malayan pit viper-bitten patients.