Arterial and venous blood sampling is equally applicable for coagulation and fibrinolysis analyses

OBJECTIVES

No consensus exists upon whether arterial and venous blood samples are equivalent when it comes to coagulation analyses. We therefore conducted a comparative cohort study to clarify if arteriovenous differences affect analyses of primary and secondary hemostasis as well as fibrinolysis.

METHODS

Simultaneous paired blood samplings were obtained from a cannula in the radial artery and an antecubital venipuncture in 100 patients immediately before or one day after thoracic surgery. Analyses of platelet count and aggregation, International Normalized Ratio (INR), activated partial thromboplastin time (APTT), antithrombin, thrombin time, fibrinogen, D-dimer, rotational thromboelastometry (ROTEM), thrombin generation, prothrombin fragment 1 + 2, and an in-house dynamic fibrin clot formation and lysis assay were performed.

RESULTS

No differences were found between arterial and venous samples for the far majority of parameters. The only differences were found in INR, median (IQR): venous, 1.1 (0.2) vs. arterial, 1.1 (0.2) (p<0.002) and in prothrombin fragment 1 + 2: venous, 289 (209) pmol/L vs. arterial, 279 (191) pmol/L (p<0.002).

CONCLUSIONS

The sampling site does not affect the majority of coagulation analyses. Small differences were found for two parameters. Due to numerically very discrete differences, they are of no clinical relevance. In conclusion, the present data suggest that both samples obtained from arterial and venous blood may be applied for analyses of coagulation and fibrinolysis.

Accuracy assessment of consecutive test strip lots for whole blood INR point-of-care instruments: clarifying the role of frozen plasma pools

Background In the Netherlands, each new lot of test strips for the CoaguChek XS is validated by a group of collaborating centers. The purpose of this study was to assess the accuracy of the international normalized ratio (INR) measured with consecutive test strip lots and the suitability of frozen plasma pools for accuracy evaluation. Methods Each year, a particular lot of CoaguChek XS test strips is used as reference lot. The reference lots have been validated with the International Standard for thromboplastin rTF/09, yielding a mathematical relationship (R1) between reference lot INR and International Standard INR. New lots are compared to the reference lot using patients' capillary blood samples, yielding a relationship (R2) between the new lot INR and the reference lot INR. INRs of the blood samples were within the 1.5-4.5 interval. In parallel, three frozen plasmas pools are analyzed with the test strips. The distance of each plasma point to the line of relationship R2 was assessed. Results Fifty-four test strip lots have been evaluated during 3 years (2014-2016). Mean INR differences between test strip lot and International Standard rTF/09 varied between -0.14 and +0.20 (-4% and +8%, respectively). A positive trend with strip lot sequence number was observed (p<0.001). In several cases, the distance of the frozen plasmas to the whole blood relationship (R2) was greater than the critical value for commutability. Conclusions Using whole blood, all evaluated test strip lots met the analytical bias criterion of ±10%. Frozen plasma pools behave differently compared to whole blood and are not suitable for assessing absolute accuracy of new CoaguChek XS test strips.

Toward a Framework for Outcome-Based Analytical Performance Specifications: A Methodology Review of Indirect Methods for Evaluating the Impact of Measurement Uncertainty on Clinical Outcomes

BACKGROUND

For medical tests that have a central role in clinical decision-making, current guidelines advocate outcome-based analytical performance specifications. Given that empirical (clinical trial-style) analyses are often impractical or unfeasible in this context, the ability to set such specifications is expected to rely on indirect studies to calculate the impact of test measurement uncertainty on downstream clinical, operational, and economic outcomes. Currently, however, a lack of awareness and guidance concerning available alternative indirect methods is limiting the production of outcome-based specifications. Therefore, our aim was to review available indirect methods and present an analytical framework to inform future outcome-based performance goals.

CONTENT

A methodology review consisting of database searches and extensive citation tracking was conducted to identify studies using indirect methods to incorporate or evaluate the impact of test measurement uncertainty on downstream outcomes (including clinical accuracy, clinical utility, and/or costs). Eighty-two studies were identified, most of which evaluated the impact of imprecision and/or bias on clinical accuracy. A common analytical framework underpinning the various methods was identified, consisting of 3 key steps: (a) calculation of "true" test values; (b) calculation of measured test values (incorporating uncertainty); and (c) calculation of the impact of discrepancies between (a) and (b) on specified outcomes. A summary of the methods adopted is provided, and key considerations are discussed.

CONCLUSIONS

Various approaches are available for conducting indirect assessments to inform outcome-based performance specifications. This study provides an overview of methods and key considerations to inform future studies and research in this area.

Warfarin in nonvalvular atrial fibrillation-Time for a change?

Warfarin is the most commonly prescribed anticoagulant in hemodialysis (HD) patients with nonvalvular atrial fibrillation (NVAF). Recent trends show that Nephrologists are increasingly prescribing novel oral anticoagulants, despite the fact that no randomized clinical trials have been conducted in dialysis patients. Difficulties maintaining international normalized ratio in the therapeutic range, increased risk of intracranial hemorrhage and concerns regarding warfarin-induced vascular calcification and calciphylaxis may be responsible. Anticoagulation quality is poor in HD patients. A variety of factors contribute to this: increased antibiotic exposure; comorbid illness; decreased adherence and vitamin K deficiency. Attempts to address this with standardized protocols have been uniformly unsuccessful. In nonadherent patients, thrice weekly observed therapy improved quality. Low-dose vitamin K supplementation improves time in the therapeutic range (TTR) in those with normal kidney function and should be studied in HD patients given their high frequency of vitamin K deficiency. Vascular and valvular calcification associated with warfarin could result from reduced carboxylation of matrix Gla protein (MGP), a well-known inhibitor of vascular calcification. Multiple observational studies also link calciphylaxis to warfarin; warfarin-induced hypercoagulability and decreased carboxylation of MGP could explain this. A large observational study, two meta-analyses, and a systematic review in HD patients with NVAF showed reduced bleeding with apixaban compared to warfarin with similar efficacy in reducing stroke and systemic embolism. Given these results, apixaban is a reasonable alternative to warfarin for anticoagulation of HD patients with NVAF, especially in those with low TTR, until data from randomized clinical trials become available.

The microINR portable coagulometer: analytical quality and user-friendliness of a PT (INR) point-of-care instrument

Regular measurement of prothrombin time as an international normalized ratio PT (INR) is mandatory for optimal and safe use of warfarin. Scandinavian evaluation of laboratory equipment for primary health care (SKUP) evaluated the microINR portable coagulometer (microINR^®) (iLine Microsystems S.L., Spain) for measurement of PT (INR). Analytical quality and user-friendliness were evaluated under optimal conditions at an accredited hospital laboratory and at two primary health care centres (PHCCs). Patients were recruited at the outpatient clinic of the Laboratory of Medical Biochemistry, St Olav's University Hospital, Trondheim, Norway (n = 98) and from two PHCCs (n = 88). Venous blood samples were analyzed under optimal conditions on the STA-R^®Evolution with STA-SPA + reagent (Stago, France) (Owren method), and the results were compared to capillary measurements on the microINR^®. The imprecision of the microINR^® was 6% (90% CI: 5.3-7.0%) and 6.3% (90% CI: 5.1-8.3) in the outpatient clinic and PHCC2, respectively for INR ≥2.5. The microINR^® did not meet the SKUP quality requirement for imprecision ≤5.0%. For INR <2.5 at PHCC2 and at both levels in PHCC1, CV% was ≤5.0. The accuracy fulfilled the SKUP quality goal in both outpatient clinic and PHCCs. User-friendliness of the operation manual was rated as intermediate, defined by SKUP as neutral ratings assessed as neither good nor bad. Operation facilities was rated unsatisfactory, and time factors satisfactory. In conclusion, quality requirements for imprecision were not met. The SKUP criteria for accuracy was fulfilled both at the hospital and at the PHCCs. The user-friendliness was rated intermediate.

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.

Precision and accuracy of point-of-care testing coagulometers used for self-testing and self-management of oral anticoagulation therapy

BACKGROUND

Oral anticoagulation therapy is monitored by the use of the International Normalized Ratio (INR). Patients who perform self-testing or self-management use a point-of-care testing (POCT) coagulometer (INR monitor) to estimate their INRs. A precondition for a correct dosage of coumarins is a correct INR estimation, and the method and apparatus used for providing the INR measurements are crucial in this context. Several studies have been published regarding the precision and accuracy of these POCT coagulometers, and have led to diverse conclusions. It is difficult and challenging to perform an overview of the literature, owing to the vast amount of papers, with differences in design, statistical analysis, etc.

OBJECTIVES

The aim of this systematic review was to analyze the current literature, especially regarding the precision and accuracy of the POCT coagulometers, to provide recommendations for clinical use and quality control, and to point out areas for future research.

METHODS

We included a total of 22 studies, of which four were characterized as high-quality studies.

RESULTS

The precision of the POCT coagulometers was generally adequate for clinical use. Their performance in terms of accuracy has to be viewed in the context of the inherent inaccuracies of INR measurements.

CONCLUSIONS

The accuracy of POCT coagulometers seems, in this respect, to be generally acceptable, and they can be used in a clinical setting.

Significance of consecutive international normalized ratio (INR) outcomes using statistical control rules in long-term anticoagulated patients. Optimization of laboratory monitoring and interpretation of borderline measurements

Analysis of serial measurements is needed to elaborate observations in all fields of medical research. In the present study, retrospective data of anticoagulated patients were used to calculate a mean of observations and control limits, X+/-1sigma and X+/-2sigma (mean+/-standard deviation). During 18 months of coagulation monitoring, 45 patients without major oral anticoagulant therapy complications, with more international normalized ratio (INR) determinations in the therapeutic range and with a normal distribution of INR values according to the Kurtosis coefficient, were selected. The cumulative distribution functions allowed us to obtain critical limits of INR with a cumulative probability (p). Control limits, calculated for a therapeutic control chart, indicated through different control rules, 1S2 or 2S1, an alarm signal to analyze the cause of INR outside the therapeutic range. Our investigation suggested that for results at the level of the therapeutic control limits, we needed at least two consecutive INR results to detect a significant over- or under-anticoagulation. The therapeutic control chart method should be a useful means in clinical practice for evaluating the statistical significance of consecutive and borderline INR outcomes. Analytical improvements and control rules applied to laboratory monitoring may help optimize drug dose administration.

Poor agreement among prothrombin time international normalized ratio methods: comparison of seven commercial reagents

BACKGROUND

Prothrombin time (PT) has long been the most popular test for monitoring oral anticoagulation therapy. The International Normalized Ratio (INR) was introduced to overcome the problem of marked variation in PT results among laboratories and the various recommendations for patient care. According to this principle, all reagents should be calibrated to give identical results and the same patient care globally. This is necessary for monitoring of single patients and for application of the results of anticoagulation trials and guidelines to clinical practice.

METHODS

We took blood samples from 150 patients for whom oral anticoagulation had been prescribed. Plasmas were separated and PTs determined by use of seven commercial reagents and four calibrator sets. The differences in results were assessed by plotting, for each possible pair of methods, the differences in INR values for each sample against the mean INR value (Bland-Altman difference plots).

RESULTS

Mean results differed significantly (P <0.001) for 17 of 21 possible paired comparisons of methods. Only two pairs of methods produced very similar results when assessed for problems of substantial differences in INR values; a significant, systematic increase in the difference with INR; and a significant systematic increase in the variation in difference with increasing INR values.

CONCLUSIONS

The agreement among several (and perhaps most) commercial INR methods is poor. The failure of current calibration strategies may severely compromise both the monitoring of individual patients and the application of oral anticoagulation guidelines and trial results to clinical practice.

Has the Quick or the Owren prothrombin time method the advantage in harmonization for the International Normalized Ratio system?

Prothrombin time (PT) is the most commonly used coagulation test in health care. We sought here to compare two major PT methods (Quick and Owren) for harmonization of International Normalized Ratio (INR) results. We measured PT with an ACL 7000 analyser. We used three Owren and three Quick reagents for PT, and estimated the International Sensitivity Index (ISI) for each reagent using two local and two manufactured ISI calibrator sets. The coagulation time was measured using five different normal plasmas to assess variation for every reagent and both methods. We studied the analytical bias for every reagent and both methods at INR = 1.0 and INR = 2.5. The mean percentage coefficient of variation of the Owren reagent ISI was 2.40% and that of the Quick reagent ISI was 12.85%. The mean percentage coefficient of variation of normal plasma seconds for the Owren method was 2.54% and that for Quick was 4.02%. The absolute error at INR = 1.0 and INR = 2.5 was 0.00 and 0.04 INR for Owren, and 0.01 and 0.16 INR for Quick. The Owren PT method has the advantage over the Quick PT method in ISI calibration, normal plasma variation, within-run analytical variation and absolute error at INR = 2.5. The INR system is more demanding on analytical quality than earlier units (Ratio,%). The data would indicate that the Owren PT method has advantages over the Quick PT method in harmonization of the INR system.

Quality specifications based on analysis of effects of performance on clinical decision-making

The graphical model for evaluation of analytical requirements for bimodal distributions, based on probit transformation and calculation of false-positive and false-negative results for assumed random and systematic analytical errors, is presented in theory. It is concluded that the bimodal model is an excellent tool for evaluation of the effect of analytical quality and, therefore, useful for estimation of analytical quality specifications for quantities used in specific clinical strategies and situations as well as based on analysis of clinical outcome.