Assessment of mutual impact of different sodium citrate concentrations and minimum specimen volume on the result of routine coagulation tests

Abstract Background: Routine coagulation assays including prothrombine time [PT] and activated partial thromboplastine time [aPTT] are influenced by two independent parameters comprising sample volume and tri-sodium citrate concentration. Objective: To evaluate minimum specimen volume requirements for routine coagulation testing with dependence on citrate concentration. Methods: An experimental study was performed on samples obtained from randomized healthy persons and patients receiving oral anticoagulant therapy. The tubes (3.2% and 3.8% sodium citrate) were filled to varying total sample volumes ranging from 3.0 to 5.0 mL and results of routine coagulation tests were compared. Findings: By using 3.8% citrate, there is a statistically significant difference in the results of PT and aPTT assays in the sample less than 80% and 90% filled compared with those that are 100% filled. There is no significant difference in PT results from a 3.2% citrate tube between fill volume of 60% and 100% as well as 70% and 100% for aPTT. Conclusion: Underfilling may significantly affect the aPTT and PT, resulting in artifactual prolongation of results, particularly in samples drawn into 3.8% citrate. This study supports the recommendations to use 3.2% citrate, because 60% of the optimum filled for PT and 70% for aPTT are acceptable.