title: Is duplicate testing for prothrombin time and activated partial thromboplastin time necessary?
abstract: To evaluate the necessity of duplicate testing for prothrombin times (PTs) and activated partial thromboplastin times (APTTs), the range of differences between duplicate sample results was analyzed on a widely used automated photo-optical coagulation instrument. Specimens with coagulation test times ranging from normal to threefold above the reference range were included. Of 1,610 PTs and 1,023 APTTs, approximately 95% of duplicates differed by 0.2 s or less and 2.0 s or less, respectively. Approximately 99% of PTs and APTTs differed by 0.4 s or less and 4.0 s or less, respectively; there were three PT and 16 APTT specimens whose duplicates differed by a greater time interval and also by more than 5% of the mean. Thus, PT and APTT testing on automated instrumentation is very precise, but occasional inaccurate single measurements could lead to errors in diagnosis or therapy.
mesh_terms: D001780:Blood Coagulation Tests; D006801:Humans; D010314:Partial Thromboplastin Time; D011517:Prothrombin Time; D011786:Quality Control; D012016:Reference Values