Internal quality control of prothrombin time in primary care: comparing the use of patient split samples with lyophilised control materials

Anne Stavelin; Per Hyltoft Petersen; Una Sølvik; Sverre Sandberg

doi:10.1160/TH09-02-0082

Thrombosis and Haemostasis, Table of Contents

Thromb Haemost 2009; 102(03): 593-600
DOI: 10.1160/TH09-02-0082

Blood Coagulation, Fibrinolysis and Cellular Haemostasis

Schattauer GmbH

Internal quality control of prothrombin time in primary care: comparing the use of patient split samples with lyophilised control materials

Anne Stavelin

¹NOKLUS, Norwegian Quality Improvement of Primary Care Laboratories, Haraldsplass Diaconal Hospital, Bergen, Norway

,

Per Hyltoft Petersen

²NOKLUS, Norwegian Quality Improvement of Primary Care Laboratories, Section for General Practice, Department of Public Health and Primary Health Care, University of Bergen, Bergen, Norway

,

Una Sølvik

²NOKLUS, Norwegian Quality Improvement of Primary Care Laboratories, Section for General Practice, Department of Public Health and Primary Health Care, University of Bergen, Bergen, Norway

,

Sverre Sandberg

²NOKLUS, Norwegian Quality Improvement of Primary Care Laboratories, Section for General Practice, Department of Public Health and Primary Health Care, University of Bergen, Bergen, Norway

³Laboratory of Clinical Biochemistry, Haukeland University Hospital, Bergen, Norway

› Author Affiliations

Abstract

Summary

Many primary care laboratories use point-of-care (POC) instruments to monitor patients on anticoagulant treatment. The internal analytical quality control of these instruments is often assessed by analysing lyophilised control materials and/or by sending patient samples to a local hospital laboratory for comparison (split sample).The aim of this study was to evaluate the utility of these two models of prothrombin time quality control. The models were evaluated by power functions created by computer simulations based on empirical data from 18 primary care laboratories using the POC instruments Thrombotrack, CoaguChek S, or Hemochron Jr. Signature. The control rules 1_2S, 1_3S, exponential weighted moving average, and the deviation limits of ± 10% and ± 20% were evaluated by their probability of error detection and false rejections. The total within-lab coefficient of variation was 3.8% and 6.9% for Thrombotrack, 8.9% and 10.5% for CoaguChek S, and 9.4% and 14.8% for Hemochron Jr. Signature for the control sample measurements and the split sample measurements, respectively. The probability of error detection was higher using a lyophilised control material than a patient split sample for all three instruments, whereas the probability of false rejection was similar. A higher probability of error detection occurred when lyophilised control material was used compared with the patient split samples; therefore, lyophilised control material should be used for internal analytical quality control of prothrombin time in primary health care.

Keywords

International normalised ratio - point-of-care testing - internal analytical quality control - computer simulation - power functions

Full Text

References

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