Use of lyophilized calibration plasmas and control blood for international normalized ratio calculation in external quality assessment of the prothrombin time.
In the Netherlands, most anticoagulant clinics (thrombosis centers) use the reagent Thrombotest with citrated venous blood for laboratory control of oral anticoagulant therapy. In a national external quality assessment scheme, artificial control blood samples were mailed to 160 participants. Each participant returned prothrombin times and international normalized ratio (INR) values for these blood samples. The author investigated whether local calibration with lyophilized plasmas could reduce the interlaboratory variation of the INR. Five lyophilized plasmas were mailed along with the control blood samples. Using a local calibration line determined with the lyophilized plasmas, the interlaboratory variation of INRs determined routinely could be reduced slightly from 5.8% to 7% coefficient of variation (CV) to 5.3% to 6.5% CV. In contrast, when a local calibration line was determined with four similar control blood samples, the interlaboratory variation of the INR was reduced substantially to 2.5% CV.
Department of Hematology, Leiden University Hospital, The Netherlands.
A M
AM
van den Besselaar
D002138:Calibration; D005612:Freeze Drying; D006801:Humans; D007753:Laboratories / Q000592:standards; D009426:Netherlands; D010949:Plasma / Q000737:chemistry; D011517:Prothrombin Time; D011786:Quality Control; D012015:Reference Standards