Semin Thromb Hemost 2005; 31(1): 59-65
DOI: 10.1055/s-2005-863806
Copyright © 2005 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA.

External Quality Assessment and the Laboratory Diagnosis of Thrombophilia

Piet Meijer1 , 2 , Frits Haverkate2
  • 1Director, ECAT Foundation, Leiden, the Netherlands
  • 2ECAT Foundation, Leiden, the Netherlands
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Publication History

Publication Date:
11 February 2005 (online)

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ABSTRACT

External quality assessment is a tool to compare the result of a particular laboratory test in relation to those of other laboratories as well as to assess the performance of a laboratory test over a prolonged period of time. We evaluated the relationship between the between-laboratory variation and the sample category (normal, borderline, and abnormal) for antithrombin, protein C, protein S, and the activated protein C resistance test. Only for antithrombin and protein S was a significant relationship (0.004 < p < 0.012) observed. The effect of the between-laboratory variation of the different sample categories on the clinical interpretation was investigated. With the exception of free protein S antigen, all variables showed a significant relationship (0.004 < p < 0.045) between the sample category and the percentage of misclassification. Because in clinical practice a stable test performance over a prolonged period of time is important, we evaluated the quality of test performance using the long-term analytical coefficient of variation (LCVa). A wide range in the LCVa was observed for antithrombin, protein C, and protein S. Less than half of the participants could fulfill the quality specification for diagnostic testing (LCVa ≤ 0.58 × total biological variation). This study shows that a more stable performance of laboratory tests involved in the screening of thrombophilia over a prolonged period of time is necessary.

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