Intraindividual variation of the International Normalized Ratio in patients monitored with a recombinant human thromboplastin

Defining a metrologically traceable and sustainable calibration hierarchy of international normalized ratio for monitoring of vitamin K antagonist treatment in accordance with International Organization for Standardization (ISO) 17511:2020 standard: communication from the International Federation of Clinical Chemistry and Laboratory Medicine-SSC/ISTH working group on prothrombin time/international normalized ratio standardization

Calibration of prothrombin time (PT) in terms of international normalized ratio (INR) has been outlined in "Guidelines for thromboplastins and plasmas used to control oral anticoagulant therapy" (World Health Organization, 2013). The international standard ISO 17511:2020 presents requirements for manufacturers of in vitro diagnostic (IVD) medical devices (MDs) for documenting the calibration hierarchy for a measured quantity in human samples using a specified IVD MD. The objective of this article is to define an unequivocal, metrologically traceable calibration hierarchy for the INR measured in plasma as well as in whole blood samples. Calibration of PT and INR for IVD MDs according to World Health Organization guidelines is similar to that in cases where there is a reference measurement procedure that defines the measurand for value assignment as described in ISO 17511:2020. We conclude that, for PT/INR standardization, the optimal calibration hierarchy includes a primary process to prepare an international reference reagent and measurement procedure that defines the measurand by a value assignment protocol conforming to clause 5.3 of ISO 17511:2020. A panel of freshly prepared human plasma samples from healthy adult individuals and patients on vitamin K antagonists is used as a commutable secondary calibrator as described in ISO 17511:2020. A sustainable metrologically traceable calibration hierarchy for INR should be based on an international protocol for value assignment with a single primary reference thromboplastin and the harmonized manual tilt tube technique for clotting time determination. The primary international reference thromboplastin reagent should be used only for calibration of successive batches of the secondary reference thromboplastin reagent.

Systematic review and meta-analysis of within-subject and between-subject biological variation data of coagulation and fibrinolytic measurands

OBJECTIVES

The diagnosis and monitoring of bleeding and thrombotic disorders depend on correct haemostatic measurements. The availability of high-quality biological variation (BV) data is important in this context. Many studies have reported BV data for these measurands, but results are varied. The present study aims to deliver global within-subject (CVI) and between-subject (CVG) BV estimates for haemostasis measurands by meta-analyses of eligible studies, by assessment with the Biological Variation Data Critical Appraisal Checklist (BIVAC).

METHODS

Relevant BV studies were graded by the BIVAC. Weighted estimates for CVI and CVG were obtained via meta-analysis of the BV data derived from BIVAC-compliant studies (graded A-C; whereby A represents optimal study design) performed in healthy adults.

RESULTS

In 26 studies BV data were reported for 35 haemostasis measurands. For 9 measurands, only one eligible publication was identified and meta-analysis could not be performed. 74% of the publications were graded as BIVAC C. The CVI and CVG varied extensively between the haemostasis measurands. The highest estimates were observed for PAI-1 antigen (CVI 48.6%; CVG 59.8%) and activity (CVI 34.9%; CVG 90.2%), while the lowest were observed for activated protein C resistance ratio (CVI 1.5%; CVG 4.5%).

CONCLUSIONS

This study provides updated BV estimates of CVI and CVG with 95% confidence intervals for a wide range of haemostasis measurands. These estimates can be used to form the basis for analytical performance specifications for haemostasis tests used in the diagnostic work-up required in bleeding- and thrombosis events and for risk assessment.

Point-of-care testing and INR within-subject variation in patients receiving a constant dose of vitamin K antagonist

Many patients treated with vitamin K antagonists (VKA) determine their INR using point-of-care (POC) whole blood coagulation monitors. The primary aim of the present study was to assess the INR within-subject variation in self-testing patients receiving a constant dose of VKA. The second aim of the study was to derive INR imprecision goals for whole blood coagulation monitors. Analytical performance goals for INR measurement can be derived from the average biological within-subject variation. Fifty-six Thrombosis Centres in the Netherlands were invited to select self-testing patients who were receiving a constant dose of either acenocoumarol or phenprocoumon for at least six consecutive INR measurements. In each patient, the coefficient of variation (CV) of INRs was calculated. One Thrombosis Centre selected regular patients being monitored with a POC device by professional staff. Sixteen Dutch Thrombosis Centres provided results for 322 selected patients, all using the CoaguChek XS. The median within-subject CV in patients receiving acenocoumarol (10.2 %) was significantly higher than the median CV in patients receiving phenprocoumon (8.6 %) (p = 0.001). The median CV in low-target intensity acenocoumarol self-testing patients (10.4 %) was similar to the median CV in regular patients monitored by professional staff (10.2 %). Desirable INR analytical imprecision goals for POC monitoring with CoaguChek XS in patients receiving either low-target intensity acenocoumarol or phenprocoumon were 5.1 % and 4.3 %, respectively. The approximate average value for the imprecision of the CoaguChek XS, i. e. 4 %, is in agreement with these goals.

Analytical accuracy and precision of two novel Point-of-Care systems for INR determination

BACKGROUND

Portable point-of-care (POC) instruments for determination of the whole blood prothrombin time (PT) have been available for the last three decades. Recently, two novel POC instruments for PT and International Normalized Ratio (INR) determination in whole blood have been manufactured. The purpose of this study was to compare INR values obtained with the novel instruments (microINR® and ProTime InRhythm™) to the INR determined with the international standard for thromboplastin rTF/09.

MATERIALS AND METHODS

In 60 patients treated with vitamin K-antagonists, venous whole blood was analysed with four different types of POC instruments including the novel ones. In the same patients, citrated plasma was analysed with the international standard rTF/09 and the manual tilt tube technique for clotting time determination. We assessed the bias of the INR read from the POC instruments relative to the international standard. To study the imprecision of the two novel POC instruments, duplicate INR determinations were performed.

RESULTS

The results obtained with the two novel POC instruments were positively correlated with those of the international standard rTF/09. However, there was a significant bias between INR read from the novel instruments and the INR determined with rTF/09 (P < 0.001). The mean bias was -13.7% (MicroINR) and -9.3% (InRhythm). The imprecision coefficient of variation in venous blood was 5.0% and 5.1%, respectively.

CONCLUSION

The imprecision of the two novel instruments is acceptable with respect to the average within-subject variation of the INR. The accuracy of the systems is borderline and should be improved by the manufacturers.

A multicenter study of plasma use in the United States

BACKGROUND

Detailed information regarding plasma use in the United States is needed to identify opportunities for practice improvement and design of clinical trials of plasma therapy.

STUDY DESIGN AND METHODS

Ten US hospitals collected detailed medical information from the electronic health records for 1 year (2010-2011) for all adult patients transfused with plasma.

RESULTS

A total of 72,167 units of plasma were transfused in 19,596 doses to 9269 patients. The median dose of plasma was 2 units (interquartile range, 2-4; range 1-72); 15% of doses were 1 unit, and 45% were 2 units. When adjusted by patient body weight (kg), the median dose was 7.3 mL/kg (interquartile range, 5.5-12.0). The median pretransfusion international normalized ratio (INR) was 1.9 (25%-75% interquartile range, 1.6-2.6). A total of 22.5% of plasma transfusions were given to patients with an INR of less than 1.6 and 48.5% for an INR of 2.0 or more. The median posttransfusion INR was 1.6 (interquartile range, 1.4-2.0). Only 42% of plasma transfusions resulted in a posttransfusion INR of less than 1.6. Correction of INR increased as the plasma dose increased from 1 to 4 units (p < 0.001). There was no difference in the INR response to different types of plasma. The most common issue locations were general ward (38%) and intensive care unit (ICU; 42%).

CONCLUSION

This large database describing plasma utilization in the United States provides evidence for both inadequate dosing and unnecessary transfusion. Measures to improve plasma transfusion practice and clinical trials should be directed at patients on medical and surgical wards and in the ICU where plasma is most commonly used.

The influence of coagulation factors on the in-treatment biological variation of international normalized ratio for patients on warfarin

BACKGROUND

Biological variation is usually estimated in healthy individuals during steady-state conditions. The aim of this study was to estimate the in-treatment biological variation of the International normalised ratio (INR) and to investigate to what extent the different levels of coagulation factors could explain this variation.

METHODS

Blood samples were collected from randomly included patients on warfarin treatment. INR was determined on a laboratory instrument (STA Compact(®)) and on three point-of-care instruments (Simple Simon(®)PT, CoaguChek(®)XS and INRatio(™)). The level of fibrinogen, and the activity of coagulation factors II, V, VII and X were determined.

RESULTS

The in-treatment within- and between-subject coefficients of variation of INR were dependent on the method and varied between 18 and 24% and 13 and 19%, respectively, and were reduced to 3.9-5.1% and 2.3-5.8%, after correction for coagulation factors which could explain 91-95% of the variance of INR.

CONCLUSIONS

The in-treatment biological variation of INR was higher than reported for healthy individuals as well as patients in a steady-state condition, but by correcting for appropriate coagulation factors it was reduced. The association between INR and coagulation factors was different for the different PT methods mainly due to different sensitivity towards FII and FVII.

Biological variation of INR in stable patients on long-term anticoagulation with warfarin

Within-individual biological variation of INR (CV(B)) was assessed in 245 selected stable warfarin-treated patients monitored by three thrombosis centers. Selection criteria were: treatment period of six months or longer before the observation period; at least six consecutive INRs within the therapeutic range of 2.0 - 3.0; interval between consecutive INR measurements of two weeks or longer; no change in warfarin dose; no changes in the patient's circumstances which may influence the INR, such as intercurrent diseases, invasive procedures, starting or stopping drugs interacting with warfarin. The minimum, maximum and mean within-individual coefficient of variation CV(B) of the INR measurements in the 245 selected patients were 0.4%, 14.5%, and 9.0%, respectively Analytical performance goals for the INR measurement (imprecision) could be derived from the mean CV(B). For a therapeutic range of 2.0 - 3.0 with warfarin, the desirable and optimum imprecision of INR determination is <4.5% CV and <2.25% CV, respectively. The biological variation and analytical performance goals have been derived using classic laboratory methods but should be applicable to point-of-care testing as well.