Assignment of international normalized ratio to frozen and freeze-dried pooled plasmas

Abstract

ObjectivesFrozen and freeze-dried plasmas may be used for local prothrombin time system calibration, for direct international normalized ratio (INR) determination, and for quality assessment. The purpose of the present study was to evaluate the usefulness of INRs assigned with various types of thromboplastins to frozen and freeze-dried pooled plasmas obtained from patients treated with vitamin K antagonists.MethodsINRs were calculated according to the international sensitivity index (ISI) model using various thromboplastins and instruments, i.e. International Standards for thromboplastin as well as six commercial reagents prepared from rabbit and bovine brain, and recombinant human tissue factor. The uncertainty of the INRs was assessed using the standard deviations of clotting times and ISI values. Commutability of the plasmas was assessed according to the approved Clinical and Laboratory Standards Institute (CLSI) Guideline EP30-A. Validation of a set of six frozen plasma pools for direct INR determination was performed according to the Subcommittee on Control of Anticoagulation of the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis (SSC/ISTH) guidelines.ResultsFor all frozen and freeze-dried plasmas, the INRs calculated with bovine thromboplastin Thrombotest were lower than the INRs assigned with other thromboplastins. With a few exceptions, the frozen and freeze-dried pooled plasmas were commutable. When the set of six frozen plasma pools was used for local calibration, the analytical bias of the INR was less than ±10% for all commercial reagents except Thrombotest.ConclusionsProcessing of fresh plasmas to prepare pooled frozen plasmas and freeze-dried plasmas may lead to different INR assignments depending on the thromboplastin used. Despite minor INR differences, a set of six frozen plasma pools could be used for local calibration by direct INR determination.

Effect of the reaction temperature on the prothrombin time and the apparent International Normalized Ratio determined with International Standards for thromboplastins

“…The use of pooled plasmas is justifiable because the previous studies have shown that pooled plasmas may replace individual plasmas for ISI determination. 7 , 12 The change of INR A per degree centigrade increased with the increasing temperature. The relationship between INR A and reaction temperature could be described by a quadratic equation.…”

“…We used one pooled plasma obtained from healthy adults and another one from patients treated with VKA (coumarin plasma) with an INR of approximately 2.8 to estimate the change of the PT ratio and the “Apparent INR” (INR A ) with the reaction temperature. The use of pooled plasmas is justifiable because the previous studies have shown that pooled plasmas may replace individual plasmas for ISI determination 7,12 . The change of INR A per degree centigrade increased with the increasing temperature.…”

“…The international standards for rabbit thromboplastin (coded RBT/16) and recombinant human thromboplastin (coded rTF/16) were obtained from the National Institute for Biological Standards and Control (Potters Bar, UK). Frozen pooled normal plasma and frozen pooled coumarin plasma were prepared as described previously 7 . Borosilicate glass test tubes, 12 × 75 mm, were obtained from Duran Wheaton Kimble (product nr 73500‐1275).…”

“…Frozen pooled normal plasma and frozen pooled coumarin plasma were prepared as described previously. 7 Borosilicate glass test tubes, 12 × 75 mm, were obtained from Duran Wheaton Kimble (product nr 73500‐1275). A glass tank (40 × 26 × 17 cm) filled with water was used as a thermostat bath.…”