Variability in international normalized ratio and activated partial thromboplastin time after injury are not explained by coagulation factor deficits.

Background: Conventional coagulation assays (CCAs), prothrombin time (PT)/international normalized ratio (INR) and activated partial thromboplastin time (aPTT), detect clotting factor (CF) deficiencies in hematologic disorders. However, there is controversy about how these CCAs should be used to diagnose, treat, and monitor trauma-induced coagulopathy. Study objectives were to determine whether CCA abnormalities are reflective of deficiencies of coagulation factor activity in the setting of severe injury.
Methods: Patients without previous CF deficiency within a prospective database at an ACS-verified Level I trauma center had CF activity levels, PT/INR, aPTT, and fibrinogen levels measured upon emergency department arrival from 2014 to 2017. Linear regression assessed how CF activity explained the aPTT and PT/INR variation. Prolonged CCA values were set as INR greater than 1.3 and aPTT greater than 34 seconds. CF deficiency was defined as less than 30% activity, except for fibrinogen, defined as less than 150 mg/dL.
Results: Sixty patients with a mean age of 35.8 (SD, 13.6) years and median New Injury Severity Score of 32 (interquartile range, 12-43) were included; 53.3% sustained blunt injuries, 23.3% required massive transfusion, and mortality was 11.67%. Overall, 44.6% of the PT/INR variance and 49.5% of the aPTT variance remained unexplained by CF activity. Deficiencies of CFs were: common pathway, 25%; extrinsic pathway, 1.7%; and intrinsic pathway, 6.7%. The positive predictive value for CF deficiencies were: (1) PT/INR greater than 1.3:4.4% for extrinsic pathway, 56.5% for the common pathway; (2) aPTT greater than 34 seconds:16.7% for the intrinsic pathway, 73.7% for the common pathway.
Conclusion: Almost half of the variances of PT/INR and aPTT were unexplained by CF activity. Prolonged PT/INR and aPTT were poor predictors of deficiencies in the intrinsic or extrinsic pathways; however, they were indicators of common pathway deficiencies.
Level of Evidence: Prognostic, level III.