Validation of Pre-analytical Stability of Specimens Requested for Various Routine Coagulation Tests

Abstract

Storage conditions, such as storage time and temperature, can affect the stability of coagulation factors and influence the results of coagulation assays. Therefore, a clinical laboratory should determine the allowable time interval between collection of the specimen and testing of the sample stored at a certain temperature. The Clinical and Laboratory Standards Institute (CLSI) guidelines (H21-A5) recommend that whole blood samples or plasma samples stored at room temperature for routine hemostasis tests or determination of coagulation factors should be analyzed within 4 hr after sample collection, with the exception of prothrombin time testing with stability up to 24 hr. However, there have been some studies suggesting samples stored for prolonged time periods are acceptable for reliable testing. For example, there were no clinically relevant changes in prothrombin time (PT) test results with up to a 24–48 hr delay. These data are practically important, because if a longer storage time were acceptable, resampling for additional coagulation testing and rejection of specimens due to prolonged delivery could be reduced. However, there are some differences between studies according to the storage conditions, testing method, and criteria for acceptability. Most studies have dealt with unspun blood samples (focusing on time from sample collection to delivery to the laboratory) or separated plasma. Therefore, these study data are not applicable to additional tests of samples with prolonged storage, considering most clinical samples are stored in the primary collection tube after initial testing. Additionally, there are few studies that include testing for fibrinogen degradation product (FDP) and coagulation inhibitors. This study aimed to investigate the stability of coagulation tests after storage of centrifuged samples in the primary collection tube with plasma remaining on top of the cells at room temperature for different time periods and to evaluate whether a longer storage period is acceptable compared with current CLSI guidelines. In this study, along with routine coagulation tests such as activated partial thromboplastin time (aPTT), prothrombin time (PT), fibrinogen, D-dimer, coagulation factors VIII (FVIII)/IX (FIX)/XI (FXI)/XII (FXII)/II (FII)/V (FV)/VII (FVII)/X (FX), and von Willebrand factor antigen (vWF antigen) and activity (vWF activity), tests such as antithrombin III (ATIII), FDP, dilute Russell’s viper venom time screening (dRVVT screen) and confirmation (confirm) were conducted.