A Comparison of Point-of-Care Instruments Designed for Monitoring Oral Anticoagulation with Standard Laboratory Methods

From Ink Pens to Computers: A Personal Look Back at Landmark Changes during 5 Decades as a Clinical Laboratory Scientist in U.S. Hemostasis Laboratories

In 2023, Seminars in Thrombosis and Hemostasis will be celebrating its 50^th anniversary, and similarly this will also mark my 5^th decade of working in, or association with, laboratories that perform hemostasis testing. My career started at a large military medical center, but I also worked at several other facilities, including military dispensaries, community hospitals, and a large academic institution. The difference between each type of hemostasis laboratory was as expected, with larger facilities having better instrumentation and more prolific test menus. However, whether one worked in a large academic center, or a small rural hospital, regulatory changes affected every clinical laboratory to the same degree. Advances in technology also eventually affected every hemostasis laboratory, but these salient changes were more likely to occur earlier at the larger institutions. As Seminars in Thrombosis and Hemostasis celebrates its 50^th anniversary, that milestone triggered recollection about those salient events that occurred during my own career in hemostasis testing. As such, I describe (my impression) the top ten landmark changes that altered laboratory practice at the facilities where I worked during the past 5 decades.

Administration of tissue plasminogen activator without coagulation results in a Chinese population

Routine coagulation test before intravenous tissue plasminogen activator (tPA) use increases the door to needle time (DNT). We sought to evaluate the safety of tPA use without coagulation results and its impact on prognosis. In our stroke registry, tPA was delivered with coagulation results from December 2015 to April 2016 and without coagulation results from May 2016 to December 2016. Differences of demographics, clinical characteristic, and prognosis between these two groups were analyzed. In addition, logistic regression analysis was conducted to identify predictors for DNT of over 60 min. A total of 201 stroke patients were included in the final analysis. Of these, 81 patients received tPA with coagulation results and 120 patients without coagulation results. Only one (0.8%) patient with abnormal coagulation results met the exclusion criteria of tPA use in patients without coagulation results. The difference of DNT between groups with (mean, 61.7 min) and without (mean, 41.9 min) coagulation results was significant (P = 0.00). The group without coagulation results had a higher rate of favorable 90-day outcome (74.2 vs 70.4%) and lower rates of symptomatic intracranial hemorrhage/nonintracranial hemorrhage (4.9 and 22.2% vs 1.7 and 19.2%) than the group with coagulation results did; these differences were not statistically significant. In multivariate analysis, only tPA use with coagulation results was the predictor for DNT of over 60 min (P = 0.0030, OR = 2.44, 95% CI 1.28-4.65). The present study suggests that tPA could be delivered safely without coagulation results in patients without suspected coagulopathy, and avoiding coagulation tests reduces significantly the DNT interval.

Comparison of two point-of-care international normalized ratio devices and laboratory method

: A number of factors contribute to interlaboratory variation of international normalized ratio (INR) results. This variability can lead to differences in clinical decision-making. This prospective cohort study evaluated the accuracy, precision, and clinical decision-making variability of two point-of-care (POC) devices (CoaguChek XS and the Coag-Sense) to a clinical laboratory method of INR measurement as the 'reference' and by using the laboratory's accuracy standard (±25% of the reference INR). Study subjects included adults taking warfarin undergoing a POC INR with each device and a laboratory INR on the same day and evaluated differences in clinical decision-making using a warfarin nomogram. A correction factor was derived for each POC method to estimate the corresponding laboratory INR for POC INRs more than 3.0. A total of 100 patient encounters (76 unique patients) included INR testing by all three methods. Both POC devices demonstrated excellent precision across the entire range (r = 0.98), but poor accuracy relative to the laboratory standard for POC INRs greater than 3.0 (accuracy CoaguChek 19% and Coag-Sense 35%). A correction factor applied to POC INRs greater than 3.0 improved accuracy to 99% for both devices. Applying the correction factor also significantly reduced differences in clinical decision-making (49-28% for CoaguChek and 56-40% for Coag-Sense, P < 0.001). Both POC devices demonstrated poor accuracy for INRs over 3.0. A device-specific, institution-specific correction factor applied to POC INRs greater than 3.0 can provide better accuracy of INR measurement and can significantly reduce variability in warfarin dosing decisions. More study is needed to assess impact on clinical adverse events.

Anticoagulation Monitoring Part 1: Warfarin and Parenteral Direct Thrombin Inhibitors

OBJECTIVE:

To review the availability, mechanisms, limitations, and clinical application of point-of-care (POC) devices used in the management of warfarin and parenteral direct thrombin inhibitors.

DATA SOURCES:

Scientific articles were identified through a MEDLINE search (1966–August 2004), manufacturer Web sites, additional references listed in articles and Web sites, and abstracts from scientific meetings.

STUDY SELECTION AND DATA EXTRACTION:

English-language literature from clinical trials was reviewed to evaluate the accuracy, reliability, and clinical application of POC monitoring devices.

DATA SYNTHESIS:

The prothrombin time expressed as the international normalized ratio (PT—INR) is a well-established test for monitoring warfarin anticoagulation. Multiple devices are available for POC testing. Because there is no universally accepted standard, the performance of each device is typically tested against a standard test performed in a reference laboratory. Performance of currently available devices, as measured by correlations to a standard reference laboratory PT—INR, may be considered very good and acceptable for use in patient care. Utilization of patient self-testing and patient self-monitoring of warfarin anticoagulation using POC devices is increasing. Parenteral direct thrombin inhibitors are typically monitored using a standard laboratory activated partial thromboplastin time. Some research has shown that POC monitoring of direct thrombin inhibitors using the ecarin clotting time is helpful for patients undergoing cardiopulmonary bypass surgery, although that test is not readily available.

CONCLUSIONS:

POC testing for anticoagulation therapy has been available for >20 years. Multiple POC devices are available to monitor warfarin. There is some variability in results between devices and between reagents used in the same device. Despite these limitations, POC monitoring of warfarin via the PT—INR is an integral part of clinical practice. Additional research evaluating POC monitoring of direct thrombin inhibitors is necessary.

Point-of-care (POC) versus central laboratory instrumentation for monitoring oral anticoagulation

Point-of-care (POC) instruments employing fingerstick whole blood to monitor patients treated with warfarin are a popular alternative to complex, central laboratory coagulation analyzers utilizing citrated plasma derived from venipuncture. We investigated the accuracy of two widely utilized POC instruments for oral anticoagulation monitoring compared with a central laboratory instrument. Instrument-to-instrument variation differed for the two POC instruments, which correlated with the central laboratory instrument, but exhibited positive bias of 0.24-0.35 INR units. Positive bias increased as the INR values increased. We conclude that clinicians should exercise caution when interpreting results generated by POC monitors, particularly at high INR values. A high POC measurement of INR does not necessarily warrant decreasing the warfarin dose. Instead, a predefined cut-off range for high INR values generated by POC instruments should mandate confirmatory testing with central laboratory instrumentation.

Point of Care: Diagnostics in Hemostasisthe Wrong Direction?

Point-of-care-testing (POCT) is performance of a laboratory assay outside the laboratory by nontrained personnel. The advantages of POCT are: more rapid medical decisions, avoidance of long sample transports, and small samples. The disadvantages of POCT are: no laboratory personnel, insufficient calibration, quality control and maintenance, poor documentation, high costs, difficult comparability POCT/central laboratory. Therefore, disposing of a 24-hour central laboratory, the POCT spectrum should be limited to the vital parameters: K+, Ca++, Na+, glucose, creatinine, blood gases, hemoglobin or hematocrit, NH3, lactate. POCT offers no advantages, if the hospital has a rapid transport system such as a pneumatic delivery to the central laboratory. The rapid diagnosis of the acute hemostasis state of a patient should be performed in the 24-hour central laboratory that is connected to all hospital wards via a good pneumatic delivery.

Analytical performance of a point-of-care device in monitoring patients on oral anticoagulation with vitamin K antagonists

BACKGROUND

[Please check the following sentence for clarity: "Point-of-care devices measuring international normalized ratio have clinical appeal, reports of 'off-label' in-hospital/primary care use report improved time to intervention/dose adjustment."]Point-of-care devices measuring international normalized ratio have clinical appeal, reports of 'off-label' in-hospital/primary care use report improved time to intervention/dose adjustment. We evaluated the accuracy and precision of a device for such multiple patient use compared to a reference laboratory.

METHODS

The point-of-care international normalized ratio result of patients on oral anticoagulation at the Vascular Surgery clinic was compared to the reference to check for statistical and clinical correlation. This was a prospective case-control study design with sample size calculated for sensitivity of 87.5%, precision 5% and desired confidence level 95%.

RESULTS

There were 168 patients tested; 55% were male, the mean age was 45.4. Sixty per cent were in the target international normalized ratio range. Tests were done for statistical and clinical correlation. The international normalized ratio range using the point-of-care device was 0.8-7.5 (reference lab 0.8-10), mean international normalized ratio was 2.22 ± 1.6 (point-of-care device) compared to 2.46 ± 1.3 (reference lab). The mean absolute difference was 0.79 ± 0.92 and the mean relative difference was 8.1% ± 1.03. Data was analysed using a Bland-Altman plot yielding a mean of 0.738 (standard deviation 0.92). Concordance between the tests was 75% with r2 = 0.52 on linear regression. Using an error grid plot, excellent clinical correlation was seen in 63.8%. In 5.4% major corrective action was needed but potentially missed if relying on the point-of-care device.

CONCLUSION

The accuracy and precision of this point-of-care device is moderate. It may have potential utility only where access to a reference lab is difficult.

Reliability of Point-of-Care Testing of INR in Acute Stroke

Background:

In the emergency department, portable point-of-care testing (POCT) coagulation devices may facilitate stroke patient care by providing rapid International Normalized Ratio (INR) measurement. The objective of this study was to evaluate the reliability, validity, and impact on clinical decision-making of a POCT device for INR testing in the setting of acute ischemic stroke (AIS).

Methods:

A total of 150 patients (50 healthy volunteers, 51 anticoagulated patients, 49 AIS patients) were assessed in a tertiary care facility. The INR’s were measured using the Roche Coaguchek S and the standard laboratory technique.

Results:

The interclass correlation coefficient and 95% confidence interval between overall POCT device and standard laboratory value INRs was high (0.932 (0.69 - 0.78). In the AIS group alone, the correlation coefficient and 95% CI was also high 0.937 (0.59 - 0.74) and diagnostic accuracy of the POCT device was 94%.

Conclusions:

When used by a trained health professional in the emergency department to assess INR in acute ischemic stroke patients, the CoaguChek S is reliable and provides rapid results. However, as concordance with laboratory INR values decreases with higher INR values, it is recommended that with CoaguChek S INRs in the > 1.5 range, a standard laboratory measurement be used to confirm the results.

International normalized ratio testing with point-of-care coagulometer in healthy term neonates

Background

Neonates routinely receive vitamin K to prevent vitamin K deficiency bleeding, which is associated with a high mortality rate and a high frequency of neurological sequelae. A coagulation screening test might be necessary to detect prophylactic failure or incomplete prophylaxis. However, venous access and the volume of blood required for such testing can be problematic. CoaguChek XS is a portable device designed to monitor prothrombin time while only drawing a small volume of blood. Although the device is used in adults and children, studies have not been performed to evaluate its clinical utility in neonates, and the reference value is unknown in this population. The objectives of the present study were to determine the reference intervals (RIs) for international normalized ratio (INR) using the CoaguChek XS by capillary puncture in healthy term neonates, to evaluate factors that correlate with INR, and to evaluate the device by assessing its ease of use in clinical practice.

Methods

This study included 488 healthy term neonates born at a perinatal center between July 2012 and June 2013. The INRs determined by CoaguChek XS were measured in 4-day-old neonates.

Results

The enrolled neonates were orally administered vitamin K 6-12 h after birth. A RI for INRs in 4-day-old neonates was established using the CoaguChek XS with a median value of 1.10 and a range of 0.90–1.30. A significant difference in the INR was noted between male (median value, 1.10; RI, 0.90–1.30) and female (median value, 1.10; RI, 0.90–1.24) neonates (p = 0.049). The INR was found to correlate with gestational age, birth weight, and hematocrit value.

Conclusions

The CoaguChek XS device is safe, fast, and convenient for performing INR assays in neonates. Our study is the first to establish a RI for INRs that were measured using the CoaguChek XS in healthy term neonates.

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.

Oral anticoagulant therapy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

The objective of this article is to summarize the published literature concerning the pharmacokinetics and pharmacodynamics of oral anticoagulant drugs that are currently available for clinical use and other aspects related to their management.

METHODS

We carried out a standard review of published articles focusing on the laboratory and clinical characteristics of the vitamin K antagonists; the direct thrombin inhibitor, dabigatran etexilate; and the direct factor Xa inhibitor, rivaroxaban

RESULTS

The antithrombotic effect of each oral anticoagulant drug, the interactions, and the monitoring of anticoagulation intensity are described in detail and discussed without providing specific recommendations. Moreover, we describe and discuss the clinical applications and optimal dosages of oral anticoagulant therapies, practical issues related to their initiation and monitoring, adverse events such as bleeding and other potential side effects, and available strategies for reversal.

CONCLUSIONS

There is a large amount of evidence on laboratory and clinical characteristics of vitamin K antagonists. A growing body of evidence is becoming available on the first new oral anticoagulant drugs available for clinical use, dabigatran and rivaroxaban.

Discrepancies in International Normalized Ratio Results between Instruments: A Model to Split the Variation into Subcomponents

BACKGROUND

Observed differences between results obtained from comparison of instruments used to measure international normalized ratio (INR) have been higher than expected from the imprecision of the instruments. In this study the variation of these differences was divided into subcomponents, and each of the subcomponents was estimated.

METHODS

Blood samples were collected at 4 different patient visits from each of 36 outpatients who were receiving warfarin treatment and were included in the study. INR was determined on 1 laboratory instrument (STA Compact®) and 3 point-of-care instruments (Simple Simon®PT, CoaguChek®XS, and INRatio™). All 4 INR instruments were compared in pairs. Linear regression was used to correct for systematic deviations. The remaining variation of the differences was subdivided into between-subject, within-subject, and analytical variation in an ANOVA nested design.

RESULTS

The mean difference between instruments varied between 1.0% and 14.3%. Between-subject variation of the differences (expressed as CV) varied between 3.3% and 7.4%, whereas within-subject variation of the differences was approximately 5% for all 6 comparisons. The analytical imprecision of the differences varied between 3.8% and 8.6%.

CONCLUSIONS

The differences in INR between instruments were subdivided into calibration differences, between- and within-subject variation, and analytical imprecision. The magnitude of each subcomponent was estimated. Within results for individual patients the difference in INR between 2 instruments varied over time. The reasons for the between- and within-subject variations of the differences can probably be ascribed to different patient-specific effects in the patient plasma. To minimize this variation in a monitoring situation, each site and patient should use results from only 1 type of instrument.

Point-of-care testing in haemostasis

Point-of-care testing (POCT) in haematology has seen a significant increase in both the spectrum of tests available and the number of tests performed annually. POCT is frequently undertaken with the belief that this will reduce the turnaround time for results and so improve patient care. The most obvious example of POCT in haemostasis is the out-of-hospital monitoring of the International Normalized Ratio in patients receiving a vitamin K antagonist, such as warfarin. Other areas include the use of the Activated Clotting Time to monitor anticoagulation for patients on cardio-pulmonary bypass, platelet function testing to identify patients with apparent aspirin or clopidogrel resistance and thrombelastography to guide blood product replacement during cardiac and hepatic surgery. In contrast to laboratory testing, POCT is frequently undertaken by untrained or semi-trained individuals and in many cases is not subject to the same strict quality control programmes that exist in the central laboratory. Although external quality assessment programmes do exist for some POCT assays these are still relatively few. The use of POCT in haematology, particularly in the field of haemostasis, is likely to expand and it is important that systems are in place to ensure that the generated results are accurate and precise.

Comparison of plasma with whole blood prothrombin time and fibrinogen on the same instrument

We compared plasma with whole blood (WB) international normalized ratio (INR) and fibrinogen using the same instrument and reagents. WBINRs were 50% higher than plasma INRs. After increasing the WB sample volume 40% and adjusting the International Sensitivity Index, WBINRs were similar to plasma INRs [adjusted WBINR = 0.99(plasma INR) - 0.02; r(2) = 0.98; n = 155], but the average difference in WB vs plasma INR was 4-fold higher than duplicate plasma INRs. Variation in hematocrit was a major determinant of the accuracy of the WBINR, with increased error at high INRs. The WB fibrinogen assay was highly dependent on the sample hematocrit (r(2) = 0.83), even after the sample volume was adjusted. Accurate WB fibrinogen measurements required a mathematical hematocrit correction. We conclude that WBINR and fibrinogen assays can be performed on point-of-care or automated analyzers, but sample volume must be adjusted to account for hematocrit. Accuracy is limited by variations in hematocrit with worsening accuracy for samples with high INRs or low fibrinogen levels.

Use of error grid analysis to evaluate acceptability of a point of care prothrombin time meter

BACKGROUND

Statistical methods (linear regression, correlation analysis, etc.) are frequently employed in comparing methods in the central laboratory (CL). Assessing acceptability of point of care testing (POCT) equipment, however, is more difficult because statistically significant biases may not have an impact on clinical care. We showed how error grid (EG) analysis can be used to evaluate POCT PT INR with the CL.

MATERIALS AND METHODS

We compared results from 103 patients seen in an anti-coagulation clinic that were on Coumadin maintenance therapy using fingerstick samples for POCT (Roche CoaguChek XS and S) and citrated venous blood samples for CL (Stago STAR). To compare clinical acceptability of results we developed an EG with zones A, B, C and D.

RESULTS

Using 2nd order polynomial equation analysis, POCT results highly correlate with the CL for CoaguChek XS (R(2)=0. 955) and CoaguChek S (R(2)=0. 93), respectively but does not indicate if POCT results are clinically interchangeable with the CL. Using EG it is readily apparent which levels can be considered clinically identical to the CL despite analytical bias.

CONCLUSION

We have demonstrated the usefulness of EG in determining acceptability of POCT PT INR testing and how it can be used to determine cut-offs where differences in POCT results may impact clinical care.

External quality assessment of prothrombin time: The split‐sample model compared with external quality assessment with commercial control material

OBJECTIVE

CoaguChek S is a point-of-care, whole-blood, prothrombin time monitor. The purpose of this study was to compare two different methods for external quality assessments of CoaguChek S.

MATERIAL AND METHODS

In the traditional external quality assessment scheme, commercial control material was sent to office laboratories and the results were compared with a method-specific target value. In the alternative external quality assessment (the split-sample survey) patient samples were analyzed on CoaguChek S at office laboratories, and venous blood samples from the same patients were analyzed at a hospital laboratory using an assigned comparison method. To obtain comparable performance criteria for the two methods, the limits for "good", "acceptable" and "poor" performance evaluation in the split-sample survey had to be expanded because of uncertainties in preanalytical factors and the comparison method.

RESULTS

In the traditional external quality assessment the total imprecision (between-office and within-office) was 8.0% at the low level (1.6 INR (International Normalized Ratio)) and 10.5% at the therapeutic level (3.4 INR). In the split-sample survey the total imprecision was 12.3% at the low level (2.1 INR) and 10.7 % at the high level (3.0 INR). Seventy-five percent of the participating office laboratories were characterized as "good" with the traditional external quality assessments, whereas the corresponding number was 73% using the split-sample model.

CONCLUSIONS

Available commercial control material for CoaguChek S is different from patient samples. This study demonstrates that split-sample survey is achievable, and is an acceptable alternative to traditional external quality assessment for point-of-care prothrombin time monitors where appropriate control material is difficult to obtain.

Novel anticoagulants and the future of anticoagulation

Since its discovery during the first half of the 20th century by biochemists at the University of Wisconsin, warfarin (along with other vitamin K antagonists) has remained the only oral anticoagulant available to patients at risk for thromboembolism. After nearly 6 decades in clinical practice, we have learned much about warfarin. Although it is highly effective for most patients, warfarin has a number of undesirable attributes: significant inter- and intra-patient variability in dose-response, a narrow therapeutic index, a slow pharmacodynamic response, and numerous interactions with both diet as well as other medications. The negative characteristics associated with warfarin have inspired many clinicians, patients, and researchers to wonder if a better alternative can be discovered. To that end, at least three novel anticoagulant compounds are in the late stages of development and several others are progressing through earlier phases of investigation. This review will summarize the latest clinical trial data pertinent to several newer antithrombotic agents and discuss recent developments that impact the safety and challenges associated with warfarin and other vitamin K antagonists (VKA).

Pharmacology and management of the vitamin K antagonists: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition)

This article concerning the pharmacokinetics and pharmacodynamics of vitamin K antagonists (VKAs) is part of the American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). It describes the antithrombotic effect of the VKAs, the monitoring of anticoagulation intensity, and the clinical applications of VKA therapy and provides specific management recommendations. Grade 1 recommendations are strong and indicate that the benefits do or do not outweigh the risks, burdens, and costs. Grade 2 recommendations suggest that the individual patient's values may lead to different choices. (For a full understanding of the grading, see the "Grades of Recommendation" chapter by Guyatt et al, CHEST 2008; 133:123S-131S.) Among the key recommendations in this article are the following: for dosing of VKAs, we recommend the initiation of oral anticoagulation therapy, with doses between 5 mg and 10 mg for the first 1 or 2 days for most individuals, with subsequent dosing based on the international normalized ratio (INR) response (Grade 1B); we suggest against pharmacogenetic-based dosing until randomized data indicate that it is beneficial (Grade 2C); and in elderly and other patient subgroups who are debilitated or malnourished, we recommend a starting dose of < or = 5 mg (Grade 1C). The article also includes several specific recommendations for the management of patients with nontherapeutic INRs, with INRs above the therapeutic range, and with bleeding whether the INR is therapeutic or elevated. For the use of vitamin K to reverse a mildly elevated INR, we recommend oral rather than subcutaneous administration (Grade 1A). For patients with life-threatening bleeding or intracranial hemorrhage, we recommend the use of prothrombin complex concentrates or recombinant factor VIIa to immediately reverse the INR (Grade 1C). For most patients who have a lupus inhibitor, we recommend a therapeutic target INR of 2.5 (range, 2.0 to 3.0) [Grade 1A]. We recommend that physicians who manage oral anticoagulation therapy do so in a systematic and coordinated fashion, incorporating patient education, systematic INR testing, tracking, follow-up, and good patient communication of results and dose adjustments [Grade 1B]. In patients who are suitably selected and trained, patient self-testing or patient self-management of dosing are effective alternative treatment models that result in improved quality of anticoagulation management, with greater time in the therapeutic range and fewer adverse events. Patient self-monitoring or self-management, however, is a choice made by patients and physicians that depends on many factors. We suggest that such therapeutic management be implemented where suitable (Grade 2B).

Clinically significant differences between point-of-care analysers and a standard analyser for monitoring the International Normalized Ratio in oral anticoagulant therapy: a multi-instrument evaluation in a hospital outpatient setting

The increasing number of patients requiring oral anticoagulant therapy has lead to an expansion in the use of point-of-care test (POCT) analysers for measuring the International Normalized Ratio (INR) for monitoring purposes. Availability of new technology inevitably leads to comparisons with standard methodologies, and studies to date have reached varying conclusions about the comparability of POCT INRs with conventional testing. We compared the performance of five POCT instruments (Hemochron Junior Signature, ProTime, CoaguChek S, INRatio and TAS) against Innovin thromboplastin on a Sysmex CA1500 automated analyser. The Hemochron Junior Signature, ProTime and CoaguChek S demonstrated strong correlation with the laboratory method (R2 > 0.94). These three analysers demonstrated higher percentages of paired results within 0.5 INR units (81.5, 92.0 and 74.0%, respectively); the INRatio and TAS demonstrated 54.2 and 62.2%, respectively. Within INR ranges of up to 2.0, 2.1-3.0, 3.1-4.0 and above 4.0, none of the POCT analysers demonstrated significant agreement with the standard method in every range. All POCT instruments showed a degree of bias and greater variation from the standard method at INR values above 3.0. These data indicate the potential for POCT analysers to generate INR values sufficiently different from conventional methods that they may impact on clinical decision-making.

INR comparison between the CoaguChek® S and a standard laboratory method among patients with self-management of oral anticoagulation

INTRODUCTION

Portable coagulation monitors have been developed to measure International Normalised Ratio (INR) in orally anticoagulated patients using capillary whole blood from a finger stick. Because of unsatisfactory precision of some of the monitors in comparison with laboratory methods new devices are being developed. In the present study we compared INR determination with the CoaguChek S device with a standard laboratory method among patients with self-management of oral anticoagulation (OAC).

METHODS

Two hundred and forty-two patients performing self-management of OAC were enrolled into this study. Parallel INR measurements were performed within one hour. Capillary INR measurements (INRcap) were done by the patients with the CoaguChek S and venous INR (INRven) by qualified medical staff using a standard laboratory method.

RESULTS

We found a correlation coefficient (r(S)) of 0.85 (95% CI: 0.81-0.88) among the 242 patients between INRven and INRcap. In 84.4% of the INR parallel measurements the difference between the two values was below 0.5 INR units. In only 2 of 242 cases the difference was >1 INR unit (1.1 and 1.3). The slope of the Passing Bablok regression line was 0.91 (95% CI: 0.83-1.0) and the y-intercept 0.06 (95% CI: -0.20-0.25). Agreement between both methods was 90.5% (95% CI: 86.8-94.2) and standard-agreement even 97.1% (95% CI: 95-99.2).

CONCLUSIONS

INR measurement with CoaguChek S device by trained patients revealed reliable results in comparison to the values obtained with a standard laboratory method.

Point-of-care antithrombotic monitoring in children

INTRODUCTION

The use of oral anticoagulant therapy is increasing in children. Managing anticoagulant therapy in children presents unique challenges, including poor venous access. The advent of point-of-care (POC) monitoring of anticoagulant therapy offers a potential solution to this challenge. This paper reviews the published literature relating to POC monitoring of oral anticoagulant therapy in children.

MATERIALS AND METHODS

A Medline search was conducted and identified key publications. Papers were reviewed with respect to their objectives, populations and POC device investigated. Study limitations were identified.

RESULTS

Five publications and one abstract were identified, reporting studies using five different POC monitors. Three studies had a strong clinical management focus. Outcome measures assessed included target therapeutic range achievement and frequency of adverse events. Correlation between POC and laboratory-based results ranged from 0.83 to 0.96. Home monitoring and self-management using POC monitors were both reported to be preferred compared to standard laboratory testing.

CONCLUSIONS

POC monitoring of oral anticoagulant therapy in children offers considerable advantages. The reviewed literature would suggest such monitoring can be performed accurately and reliably. The impact of quality control issues, such as calibration of thromboplastin ISI in POC devices, has not been explored in a paediatric population. Further studies are needed to clarify such issues and confirm the safety, reliability and efficacy of POC monitoring of oral anticoagulant therapy in children, including its home monitoring and self-management programs.

Search for Predictors of Nontherapeutic INR Results with Warfarin Therapy

BACKGROUND

The effectiveness and safety of warfarin require maintaining an international normalized ratio (INR) within the therapeutic range.

OBJECTIVE

To identify predictors of nontherapeutic INR results in patients receiving warfarin.

METHODS

A retrospective study was conducted using 350 ambulatory care patients from a broad geographic region, all receiving long-term warfarin therapy and followed in a tertiary-care cardiology clinic. Possible predictors of nontherapeutic INR results (gender, age, body weight, body mass index, height, race, tobacco use, alcohol use, warfarin dose, therapeutic indication, regimen intensity, INR monitoring frequency/category, interacting medications, adverse events) were assessed with logistic regression models. Subset analysis involved 146 patients concurrently monitored with capillary whole blood INR (CoaguChek).

RESULTS

As measured on venous specimens, 52% (182/350) of the patients had subtherapeutic INR results and 13% (44/350) had supratherapeutic INR results despite frequent (≤4 wk) monitoring in 75% of the patients. Due to the small sample size, supratherapeutic INR results could not be further analyzed. Of 19 predictors tested, only daily warfarin dose (p < 0.02) and regimen intensity (p < 0.03) were significant independent and additive predictors of subtherapeutic results. Patients on the high-intensity regimen (INR 2.5–3.5) and receiving warfarin ≤6 mg/day had >50% risk of having subtherapeutic INR results. Subtherapeutic CoaguChek results were independent predictors of subtherapeutic venipuncture INR results in the subset (p = 0.001).

CONCLUSIONS

In the absence of readily identifiable predictors, only higher warfarin dosing and/or more frequent monitoring (possibly with point-of-care/home monitoring devices) may minimize the time that INRs are subtherapeutic, especially in patients receiving low-dose and/or high-intensity anticoagulation therapy.

Comparison of laboratory and immediate diagnosis of coagulation for patients under oral anticoagulation therapy before dental surgery

Background

Dental surgery can be carried out on patients under oral anticoagulation therapy by using haemostyptic measures. The aim of the study was a comparative analysis of coagulation by laboratory methods and immediate patient diagnosis on the day of the planned procedure.

Methods

On the planned day of treatment, diagnoses were carried out on 298 patients for Prothrombin Time (PT), the International Normalised Ratio (INR), and Partial Thromboplastin Time (PTT). The decision to proceed with treatment was made with an INR < 4.0 according to laboratory results.

Results

Planned treatment did not go ahead in 2.7% of cases. Postoperatively, 14.8% resulted in secondary bleeding, but were able to be treated as out-patients. 1.7% had to be treated as in-patients. The average error between the immediate diagnosis and the laboratory method: 95% confidence interval was -5.8 ± 15.2% for PT, -2.7 ± 17.9 s for PTT and 0.23 ± 0.80 for INR. The limits for concordance were 9.4 and -21.1% for PT, 15.2 and -20.5 s for PTT, and 1.03 and -0.57 for INR.

Conclusion

This study showed a clinically acceptable concordance between laboratory and immediate diagnosis for INR. Concordance for PT and PTT did not meet clinical requirements. For patients under oral anticoagulation therapy, patient INR diagnosis enabled optimisation of the treatment procedure when planning dental surgery.

Improving the outcomes of anticoagulation in rural Australia: an evaluation of pharmacist-assisted monitoring of warfarin therapy

OBJECTIVE

The aim of this project was to assess whether rural pharmacist involvement in the management of patients receiving warfarin has the potential to lead to safer and more effective anticoagulation, and is valued and welcomed by patients and their general practitioners (GPs).

METHODS

A convenience sample of rural pharmacists was trained in the use of the CoaguChek S International Normalized Ratio (INR) monitor and then conducted pharmacy-based testing for approximately 3 months. Two types of testing were performed in the pharmacy: (i) comparison testing was defined as pharmacy-based tests taken within 4 h of conventional laboratory testing or (ii) additional testing, which was a pharmacy-based test with no direct comparison laboratory test taken. Pharmacists, GPs and patients completed anonymous satisfaction surveys after the completion of the pharmacy-based testing.

RESULTS

Pharmacists from 16 rural pharmacies were trained to use the CoaguChek S monitor. During the trial period, 518 INR tests were performed in the pharmacies on 137 different patients. A total of 120 tests were evaluated against results from laboratory testing. The pharmacy-based INR values were significantly correlated with the laboratory INR values (mean of 2.32+/-0.77 and 2.32+/-0.59 respectively; r=0.88, P<0.0001). A total of 398 additional pharmacy-based tests were conducted in the pharmacy and 8.5% of the additional tests resulted in a subsequent dosage change. The monitoring was well received by pharmacists, GPs and patients.

CONCLUSIONS

The results of the trial were very positive. The CoaguChek S monitor in pharmacy-based testing performed accurately compared with conventional laboratory testing. Further research needs to be conducted on the impact of community pharmacy-conducted INR monitoring on patient care and outcomes.

[Portable coagulometers: a systematic review of the evidence on self-management of oral anticoagulant treatment]

BACKGROUND AND OBJECTIVE

We aimed to systematically review the scientific evidence about the use of portable coagulometers for patient's self-management of oral anticoagulant treatment.

MATERIAL AND METHOD

Systematic review of scientific evidence available from MEDLINE'S, DARE's, HTA-Database's, NHS-EED's and The Cochrane Library' s bibliographic databases, from their origin to March 2003. Randomized control trials (RCT) and Quasi-Experimental trials were selected provided that they compared patients in self-management with patients under usual care. The quality of scientific evidence was elicited using the Scottish Intercollegiate Guideline Network (SIGN) recommendations, whilst efficacy and security were descriptively summarized.

RESULTS

Twelve (7 RCT and 5 quasi-experimental trials) articles were found, and only two of them provided grade A recommendation. Patients under self-management remained the same or more time in the therapeutic range. The incidence of adverse effects in self-management patients was the same or less than that in patients under usual care.

CONCLUSIONS

The quality of the scientific evidence is heterogeneous. For selected patients, patient's self-management is at least as effective and safe as usual care. New oral anticaogulants, which have shown promising results, should be scrutinized for future changes in service provision.

Importance of device evaluation for point-of-care prothrombin time international normalized ratio testing programs

OBJECTIVE

To determine the accuracy of 2 commercially available point-of-care devices relative to plasma international normalized ratio (INR) values.

PATIENTS AND METHODS

Point-of-care INR testing was performed with the CoaguChek and ProTime 3 devices in consecutive patients attending an anticoagulation clinic between June 18, 2003, and August 6, 2003. Results were compared with plasma INRs using a sensitive thromboplastin (International Sensitivity Index, 1.0).

RESULTS

Ninety-four patients agreed to participate in the study. Relative to the plasma INR, values were in agreement +/-0.4 INR unit 82% and 39% of the time for the CoaguChek and ProTime 3 devices, respectively. The mean +/- SD CoaguChek INRs were 0.2+/-0.31 unit lower, whereas ProTime 3 INRs were 0.8+/-0.68 unit higher than plasma INR values. Treatment decisions based on these data would have resulted in inappropriate dose adjustments 10% and 22% of the time for these 2 respective devices. Correlation with plasma was greater for the CoaguChek (r2=0.90) compared with the ProTime 3 device (r2=0.73).

CONCLUSIONS

Optimal warfarin treatment requires accurate measurement of the INR. The choice of a point-of-care device for INR management depends on the reliability of INR data generated by the device.

Agreement of a new whole-blood PT/INR test using capillary samples with plasma INR determinations

PURPOSE

The objective of the study was to compare in anticoagulated patients the international normalized ratio (INR) measured with a new capillary whole-blood device, the i-STAT Portable Clinical Analyser, with conventional plasma INR obtained from the central laboratory.

PATIENTS AND METHODS

Between-cartridge variability was first determined with two lyophilized controls with INR levels of 1.60 and 2.75 (n=10). Next, in 35 patients under different intensities of oral anticoagulation, capillary blood INR was measured with two i-STAT devices and was compared to central laboratory plasma INR (Innovin reagent and BCS analyser).

RESULTS

Between-cartridge coefficients of variation were 5% (95%, CI 3.4-9.1) and 3% (95%, CI 2.1-5.5) at INR levels of 1.60 and 2.75. Mean INR difference between the two i-STAT devices was 0.1, and the correlation coefficient was 0.98. Between i-STAT and central laboratory INR, the correlation coefficient was 0.95. Bias values were 0.04, 0.2, and -0.04 at INR levels of 2.0, 2.5, and 3.5, respectively.

CONCLUSION

The INR measured with the i-STAT Portable Clinical Analyser is precise and compares well with plasma INR performed in a central laboratory.

The pharmacology and management of the vitamin K antagonists: the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy

This article concerning the pharmacokinetics and pharmacodynamics of vitamin K antagonists (VKAs) is part of the Seventh American College of Chest Physicians Conference on Antithrombotic and Thrombolytic Therapy: Evidence-Based Guidelines. The article describes the antithrombotic effect of VKAs, the monitoring of anticoagulation intensity, the clinical applications of VKA therapy, and the optimal therapeutic range of VKAs, and provides specific management recommendations. Grade 1 recommendations are strong, and indicate that the benefits do, or do not, outweigh the risks, burdens, and costs. Grade 2 suggests that individual patient's values may lead to different choices (for a full understanding of the grading see Guyatt et al, CHEST 2004; 126:179S-187S). Among the key recommendations in this article are the following: for dosing of VKAs, we suggest the initiation of oral anticoagulation therapy with doses between 5 and 10 mg for the first 1 or 2 days for most individuals, with subsequent dosing based on the international normalized ratio (INR) response (Grade 2B). In the elderly and in other patient subgroups with an elevated bleeding risk, we suggest a starting dose at < or = 5 mg (Grade 2C). We recommend basing subsequent doses after the initial two or three doses on the results of INR monitoring (Grade 1C). The article also includes several specific recommendations for the management of patients with INRs above the therapeutic range and for patients requiring invasive procedures. For example, in patients with mild to moderately elevated INRs without major bleeding, we suggest that when vitamin K is to be given it be administered orally rather than subcutaneously (Grade 1A). For the management of patients with a low risk of thromboembolism, we suggest stopping warfarin therapy approximately 4 days before they undergo surgery (Grade 2C). For patients with a high risk of thromboembolism, we suggest stopping warfarin therapy approximately 4 days before surgery, to allow the INR to return to normal, and beginning therapy with full-dose unfractionated heparin or full-dose low-molecular-weight heparin as the INR falls (Grade 2C). In patients undergoing dental procedures, we suggest the use of tranexamic acid mouthwash (Grade 2B) or epsilon amino caproic acid mouthwash without interrupting anticoagulant therapy (Grade 2B) if there is a concern for local bleeding. For most patients who have a lupus inhibitor, we suggest a therapeutic target INR of 2.5 (range, 2.0 to 3.0) [Grade 2B]. In patients with recurrent thromboembolic events with a therapeutic INR or other additional risk factors, we suggest a target INR of 3.0 (range, 2.5 to 3.5) [Grade 2C]. As models of anticoagulation monitoring and management, we recommend that clinicians incorporate patient education, systematic INR testing, tracking, and follow-up, and good communication with patients concerning results and dosing decisions (Grade 1C+).

Home prothrombin time monitoring: a literature analysis

The anticoagulant activity of warfarin sodium is monitored by the prothrombin time (PT) using the international normalized ratio (INR). Standard oral anticoagulant therapy monitoring requires frequent patient visits to physicians' offices and/or laboratories to optimize warfarin dosage. Home PT monitoring by patients can increase testing frequency and may thus decrease complications associated with oral anticoagulant therapy. Clinical studies suggest that home PT monitoring is more effective than uncoordinated management and is as effective as care through specialized anticoagulation clinics for keeping INRs within a therapeutic range. There are accurate and reliable instruments available, but paramount to the success of home PT monitoring is sound patient selection, appropriate patient training, and consistent quality control.

Accuracy and clinical usefulness of the near-patient testing CoaguChek S international normalised ratio monitor in rural medical practice

OBJECTIVE

To compare the accuracy and clinical usefulness of the near-patient testing CoaguChek S INR monitor in rural medical practice. DESIGN, SETTING AND MAIN OUTCOME MEASURES: General practices were identified through Australian university departments of rural health. Study investigators trained general practitioners and/or practice nurses in the use of the CoaguChek S INR monitor. General practices obtained a fingerprick sample for testing with the INR monitor to compare with conventional pathology testing for accuracy. An evaluation questionnaire was administered to users of the machine to assess ease of use and clinical usefulness.

RESULTS

A total of 169 patients from 15 general practice sites provided 401 paired (CoaguChek S and laboratory) INR results. The CoaguChek S was found to be accurate when compared to laboratory INR (r = 0.89), despite complicating variables such as multiple users of the monitor and multiple laboratories used for comparison with the CoaguChek S INR. Overall, 88% of dual INR measurements were within 0.5 INR units of each other. For laboratory INR </= 1.9, 2.0-3.5 and >/= 3.6, 97%, 90% and 57% of readings were within 0.5 INR units, respectively. Clinical agreement occurred 93% and 90% of the time against published expanded and narrow criteria, respectively.

CONCLUSIONS

The routine use of near-patient testing, with appropriate training and quality assurance programs, has the potential to increase the safety and efficacy of warfarin therapy in rural and remote communities.

Evaluation of a Point-of-Care coagulation analyzer on patients undergoing cardiopulmonary bypass surgery

STUDY OBJECTIVE

To evaluate a point-of-care (POC) coagulation monitoring analyzer (CoaguChek Pro DM) in patients undergoing cardiopulmonary bypass (CPB).

DESIGN

Prospective, blinded study.

SETTING

University hospital.

PARTICIPANTS

32 patients scheduled for elective cardiac surgery with CPB.

INTERVENTION

Arterial blood samples were drawn four times: preoperatively, postinduction, and 10 minutes and 60 minutes after reversal of heparin with protamine.

MEASUREMENTS AND MAIN RESULTS

Activated partial thromboplastin time (aPTT) and prothrombin time (PT) were measured with a point-of-care system--CoaguChek Pro DM as well as with the Core Laboratory facility using a MD180 analyzer. A total of 128 consecutive paired analyses were conducted. There was very good agreement of the point-of-care-based monitoring of aPTT and PT with the Core Laboratory-based monitoring of aPTT and PT (positive correlations by linear regression analysis: r2 = 0.83 and 0.92, respectively). The turn-around time (time from blood sampling until availability of data for the anesthesiologists) was significantly shorter for the point-of-care system (averaging <10 min) than for the Core Laboratory system (averaging >30 min).

CONCLUSION

CoaguChek Pro DM is a reliable and time-efficient point-of-care system for monitoring coagulation of patients undergoing CPB. The use of this system may improve patient care in this group through timely and accurate clinical decisions.

Accuracy, reproducibility and clinical utility of the CoaguChek S portable international normalized ratio monitor in an outpatient anticoagulation clinic

The accuracy and reproducibility of the CoaguChek S, and its clinical agreement with conventional laboratory international normalized ratio (INR) determination, were evaluated in an outpatient anticoagulation clinic setting. Forty-three patients provided 248 paired INR measurements for analysis. The paired results were highly correlated (r = 0.90). The mean coefficient of variation for the CoaguChek S for a random sample of 21 patients with three repeated tests each, was 4%. Clinical applicability was also measured by discrepant INR values, as defined in the literature by expanded and narrow agreement, and by INR values resulting in a different clinical decision by a blinded haematology registrar. Expanded agreement and narrow agreement between the two INR values occurred 90 and 88% of the time, respectively. The stricter criteria set down by the clinician resulted in 73% of paired results producing the same dosage decision. The CoaguChek S displayed good correlation with laboratory determination of INR and compared relatively well with expanded and narrow clinical agreement criteria.