Is duplicate testing for prothrombin time and activated partial thromboplastin time necessary?

Keshgegian, A.A.; Mann, J.M.; Cooper, J.H.

Archives of Pathology and Laboratory Medicine 110(6): 520-522

1986


ISSN/ISBN: 0003-9985
PMID: 3754725
Document Number: 273712
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.

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