International Sensitivity Index Research Articles

A-373 Comparison of the CoaguChek ® and Coag-Sense ® PT2 Meter Point of Care INR Devices

Abstract Background Warfarin monitoring may be done at the point-of-care (POC) at home, in a clinic environment, or be performed using plasma specimens in a central laboratory. With a goal of standardizing International Normalization Ratio (INR) measurements and improving data integrity by enabling electronic transmission of results from any location, we evaluated two POC INR devices against an internal plasma INR reference method. Methods We conducted a multicenter study to test the accuracy of two commercially available point of care devices: Coag-Sense PT2 Meter (Coagusense, Inc., Fremont, CA) and CoaguChek XS Pro or XS Plus (Roche Diagnostics, Indianapolis, IN) compared with plasma INR values among warfarin treated patients. Bias and linear regression analysis were assessed for device-plasma INR comparisons. Warfarin dosing decisions were assessed for each device compared to an internal plasma INR reference method (Instrumentation Laboratories ACLTOP 500, 550, 750 analyzers (Werfen Diagnostics, Bedford MA) in one of three CLIA-certified laboratories. The thromboplastin used at our institution for INR measures is HemosIL RecombiPlasTin 2G (R2G) reagent (Werfen Diagnostics, Bedford MA) which has an International Sensitivity Index (ISI) of 1.0. Results Two hundred ninety-nine warfarin patients treated across three Mayo Clinic sites agreed to participate in the study. Common anticoagulant indications were atrial fibrillation (63.9%), venous thromboembolism (21.7%) and heart valve prosthesis (15.4%) with a 2.0–3.0 INR target range for 93.6% of patients. For the CoaguChek devices, 81.3% of values fell within 0.2 INR units of plasma INR referent and 95.3% within 0.4 units. The correlation between CoaguChek whole blood and plasma INR was excellent (R2 = 0.93). For the Coag-Sense device, 34.1% of values fell within 0.2 INR units and 60.2% within 0.4 INR units of plasma INR values, with a slightly weaker correlation between Coag-Sense whole blood and plasma INR (R2 = 0.83; P < 0.0001). Mean (± standard deviation) deviation from plasma INR was 0.04 ± 0.2 for CoaguChek compared to 0.4 ± 0.3 for Coag-Sense (P < 0.0001). The difference between POC devices was largely attributed to systematic negative bias between Coag-Sense and ACL TOP plasma INR values. Using the plasma INR as the reference method for dosing decision making, appropriate dosing recommendations would have occurred for 97.7% of CoaguChek and 81.6% of Coag-Sense results. Conclusion Compared to our institution's plasma reference method, INR values obtained from the CoaguChek devices (XS Pro and XS Plus) exhibited less systematic bias compared to the Coag-Sense values. This translates to greater percentage of concordant management decisions between POC and laboratory plasma INR methods when the CoaguChek device is used.

Levels of some coagulation parameters among apparently healthy Medical Laboratory Science undergraduate students of Rivers State University, Port Harcourt

Introduction: Prothrombin time (PT), International normalized ratio (INR) and activated partial thromboplastin time (APTT) are screening tests used to evaluate the overall integrity of the intrinsic, extrinsic and common coagulation pathway as well as monitoring and management of coagulation disorders. This study was aimed at assessing the PT, INR and APTT among apparently healthy undergraduate Medical Laboratory Science students of Rivers State University, Port Harcourt. Materials and Methods: A total of 100 apparently healthy undergraduate Medical Laboratory Science students of Rivers State University, Port Harcourt comprising of 44 males and 56 females within the age range of 17-40 years were recruited for this study. Five milliliters (5ml) of venous blood was collected from each participant using a standard venipuncture technique into a vacutainer bottle containing 3.2% tri-sodium citrate anticoagulant in a ratio of 1:9 of the anticoagulant and the blood and mixed thoroughly. Prothrombin time and activated partial thromboplastin time were determined by clotting method using the Helena C4 semi-automated, photo-optical coagulation analyzer and the Agappe thromboplastin test kit manufactured by Agappe Diagnostics Switzerland while INR was calculated by using the ratio of the study subjects’ PT to the mean of control PT raised to the power of the reagent international sensitivity index (ISI). The data obtained was analyzed using Graphpad Prism Software version 6.00. Data was presented as means, median, range and standard deviation. Results: The mean ± SD of the PT, INR and APTT were 12.9± 1.624s, 1.01±0.1281 and 37.99±8.898s in the same order. The reference intervals obtained for PT, INR and APTT were 9.7-16.2s, 0.8-1.3 and APTT 20.2-55.8s in the same order. The lower limits were within the ranges established by previous researchers while the upper limits were higher. The age range 21-25 had the highest frequency count (54), which was followed by <20 (26), 26-30 (17) and then <30 (3). The overall mean values for the age groups were within the established normal values and as such no statistically significant difference was observed between the various groups. Conclusion: This study has established the mean values and reference intervals of PT, INR and APTT for apparently healthy Medical Laboratory Science undergraduate students of Rivers State University, Port Harcourt as well as established that age does not have any significant effect on PT, INR and APTT. Due to geography, lifestyle, and genetic diversity, it is recommended that each laboratory establishes geography-specific reference intervals for PT, INR and APTT.

Estimating the measurement uncertainties of the international sensitivity index of 12 thromboplastins through Monte Carlo simulation

BackgroundMeasurement uncertainty (MU) estimation has become an important process in clinical laboratories; however, calculating the MUs of the international sensitivity index (ISI) of thromboplastins is difficult because of the complex mathematical calculations required in calibration. Therefore, this study quantifies the MUs of ISIs through the Monte Carlo simulation (MCS), which involves random sampling of numerical values to solve a complex mathematical calculation. MethodsEighty blood plasmas and commercially available certified plasmas (ISI Calibrate) were used to assign the ISIs of each thromboplastin. Prothrombin times were measured using reference thromboplastin and 12 commercially available thromboplastins (Coagpia PT-N, PT Rec, ReadiPlasTin, RecombiPlasTin 2G, PT-Fibrinogen, PT-Fibrinogen HS PLUS, Prothrombin Time Assay, Thromboplastin D, Thromborel S, STA-Neoplastine CI Plus, STA-Neoplastine R 15, and STA-NeoPTimal) with two automated coagulation instruments: ACL TOP 750 CTS (ACL TOP; Instrumentation Laboratory, Bedford, MA, USA) and STA Compact (Diagnostica Stago, Asnières-sur-Seine, France). Then, the MUs of each ISI were simulated through MCS. ResultsThe MUs of ISIs ranged from 9.7 % to 12.1 % and 11.6 % to 12.0 % when blood plasma and ISI Calibrate were used, respectively. For some thromboplastins, the ISI claimed by manufacturers significantly differed from the estimated results. ConclusionsMCS is adequate to estimate the MUs of ISI. These results would be clinically useful for estimating the MUs of the international normalized ratio in clinical laboratories. However, the claimed ISI significantly differed from the estimated ISI of some thromboplastins. Therefore, manufacturers should provide more accurate information about the ISI value of thromboplastins.

Thromboplastin calibration revisited to look for possible revision of the World Health Organization recommendations

BackgroundThromboplastin calibration is essential to determine the international sensitivity index required to calculate the international normalized ratio (INR). The procedure for calibration recommended by the World Health Organization (WHO) calls for the selection of patients on stable anticoagulation in the range of 1.5 to 4.5 INR. These patients are difficult to be recruited as the conventional therapeutic interval for warfarin is 2.0 to 3.0. A possible solution could be including patients with less intense anticoagulation in the calibration. ObjectivesWe sought to investigate the impact of this amended procedure on the parameters of calibration. MethodsEight data sets from previous calibrations of a rabbit thromboplastin that included patients on anticoagulation as required by WHO were used for this pilot study. Parameters of calibration as determined by the full data sets are identified as “full calibrations” and are considered reference. Each of the data sets were used to recalculate the calibration parameters after including patients with INRs of <4.0, <3.5, or <3.0, which were identified as “trimmed calibrations” and compared with those from the full calibrations. ResultsThere was marginal variation of the international sensitivity index, CV, and INR that can be hardly of practical significance. CV was the most affected parameter, which increased from the full to the trimmed <3.0 calibration, but never exceeded the 3% cutoff value recommended by WHO. ConclusionsShould the results of this pilot study be confirmed for the calibration of other thromboplastins, revision of the WHO recommendations to include patients with INR from 1.5 to 4.0 is warranted.

English

BACKGROUND Prothrombin time (PT) is routinely used as a test of coagulation. Thromboplastin is the key ingredient in the reagent for this test. Prothrombin time international normalized ratio (INR) readings can vary according to the thromboplastin used in the reagent. The composition of thromboplastin reagents can influence the sensitivity of each batch of reagents. Various thromboplastin reagents having different international sensitivity index (ISI) values are available now. This study was intended to evaluate the effect of different thromboplastins on INR reading for mitral valve replaced patients under stable oral anticoagulant therapy. METHODS The study was conducted on the citrated plasma received from the mitral valve replaced patients having stable international ratio between 2 to 3 for three months. 62 samples were collected from the clinical pathology laboratory, Govt. Medical College, Trivandrum. Each sample was tested with different thromboplastin reagents having international sensitivity index 1.0, 1.1 and 1.6 by measurement of the prothrombin time and conversion into international normalized ratio. The INR obtained from the thromboplastin with international sensitivity index 1.0 was considered as the standard. INR results obtained from samples tested with thromboplastin reagents with ISI 1.1 and 1.6 were compared with the standard by using analysis of variance (ANOVA) and Dunnett’s post hoc tests. RESULTS Sixty-two samples were tested with the thromboplastin reagent having ISI – 1.0, the mean INR is 2.42, for ISI – 1.1 mean INR value is 2.53 and for ISI 1.6, the mean INR value is 3.19. While comparing the mean value of INR for different reagents using ANOVA, the F value was 14.86, which was significant. P value less than 0.01. In the Dunnett post hoc test, the P value of difference between ISI 1.0/1.6 was &lt; 0.01. Between ISI 1.1/1.6 also the P value is &lt; 0.01. Both of these were significant. The P value of difference between the reagents having ISI 1.0 and 1.1 is 0.838 which denotes no significant difference. CONCLUSIONS In conclusion, the thromboplastin reagent with ISI 1.0 or nearest to 1.0 is most desirable for accurate INR report. KEYWORDS Prothrombin Time, International Sensitivity Index, International Normalized Ratio

Features of biochemical parameters in healthy and patients with type 1 diabetes mellitus with different levels of albumin in the urine

The use of multi-label biochemical panels is justified by the fact that different markers reflect the severity of various pathological processes (disorders of carbohydrate and fat metabolism), which in their interaction are indicators of decompensation of a single pathology – diabetes in particular. The aim of the work was to study the differences in biochemical parameters in healthy and patients with type 1 diabetes mellitus (T1D) depending on the level of albumin in the urine. 78 men and 62 women aged 22-26 years, patients with diabetes mellitus type 1, who were hospitalized in the therapeutic department в № 1 and № 2 of Vinnytsia Regional Highly Specialized Endocrinology Center and 8 practically healthy men and 13 practically healthy women of the same age were examined. The level of microalbuminuria was determined in all patients by enzyme-linked immunosorbent assay. Fasting blood glucose and 2 hours after a meal were determined by enzymatic, amperometric analysis on a biochemical analyzer Biosen C_Line, manufactured by EKF Diagnostic (Germany). The average value of blood glucose was calculated mathematically. To determine glycated hemoglobin (HbA1c), we used the method of high performance liquid chromatography on a D 10 analyzer, manufactured by Bio-Rad (USA). The International Normal Ratio (INR) was determined using a set of reagents to determine the prothrombin time, prothrombin ratio and international sensitivity index, which is specified in the passport to the set (manufacturer of PC-K-TEST "Granum"). Total cholesterol and triglycerides were determined by colorimetric photometric method (using enzymes) on a biochemical analyzer using standard kits from Olympus AU480 (USA). Statistical processing of the results was performed in the license package "Statistica 5.5", using non-parametric evaluation methods. When comparing the level of biochemical parameters between patients with T1D and normo-, microalbuminuria and proteinuria with healthy men or women, patients found higher values: fasting glucose (in men – by 29.1 %, 30.9 % and 42.0 %; in women – by 29.7 %, 33.2 % and 46.0 %); glucose 2 hours after exercise (for men – by 27.4 %, 30.8 % and 36.1 %; for women – by 30.4 %, 32.4 % and 40.2 %); the average value of glucose (for men – by 26.2 %, 30.8 % and 39.3 %; for women – by 28.7 %, 34.0 % and 43.1 %); glycated hemoglobin (47.8 %, 48.8 % and 45.8 % for men; 27.2 %, 50.2 % and 54.4 % for women). Also, in patients with T1D men and proteinuria and women with normoalbuminuria and proteinuria compared with healthy men or women found higher cholesterol values (17.8 % in men and 7.6 % and 26.0 % in women); and in patients with T1D men with proteinuria compared to healthy men – 31.3 % higher triglyceride levels. When comparing the level of biochemical parameters between patients with T1D in men or women with proteinuria, higher values were found: fasting glucose compared with men with normoalbuminuria by 22.2 % and with women with normoalbuminuria by 30.3 % and microalbuminuria by 23.7 %; the average value of glucose compared with men with normoalbuminuria by 20.8 % and microalbuminuria by 14.0 %; glycated hemoglobin compared to women with normoalbuminuria by 15.9 %; compared with men with normoalbuminuria and microalbuminuria – by 24.8 % and 20.3 %, or with women with normoalbuminuria and microalbuminuria – by 24.9 % and 28.0 %; triglycerides compared with men with normoalbuminuria by 23.0 %. When comparing the sex differences in the level of biochemical parameters between healthy or between patients with T1D and normo-, microalbuminuria and proteinuria in men and women, only higher values of glycated hemoglobin by 14.1 % in women with proteinuria and total cholesterol by 8.3 % in women with normoalbuminuria were found. Thus, between healthy and patients with T1D and different levels of albuminuria there are differences in biochemical parameters, and they are greater the higher the level of albumin in the urine.

Evaluation of STA-NeoPTimal, an extraction thromboplastin reagent with ISI close to 1.

The prothrombin time (PT) is the most requested test to investigate patients with congenital or acquired coagulopathies or to monitor oral anticoagulant therapy. However, thromboplastins can show markedly different responsiveness to the defects induced by vitamin K antagonist (VKA) therapy and are thus characterized by their ISI (International Sensitivity Index). INR results are optimal for patients under VKA but for patients screened for other reasons expressing PT results as ratio can be more appropriate. As it is very difficult to define the PT results reporting unit from the PT testing request, it would be ideal to use a thromboplastin with ISI=1. The study aims to compare our reference PT reagent with two candidate thromboplastins with ISI close to 1. We compared 3 different thromplastins: two rabbit brain extracted based reagents (STA-Neoplastine CI Plus, with ISI=1.26, routinely used in our laboratory and STA-NeoPTimal with ISI=1.01) and a recombinant thromboplastin (STA-Neoplastine R with ISI=0.97). The comparison was done on 175 samples: 75 from individuals without coagulation defects and 100 from patients under VKA. STA-NeoPTimal and STA-Neoplastine R well correlate to our reference, STA-Neoplastine CI Plus: regression equations are y=1.186x-0.1351, r2 =.9454 and y=1.1432x-0.1554, r2 =.9951, respectively. The lowest bias on INR results was obtained with STA-NeoPTimal reagent (interval: -0.7/+0.4). We conclude that STA-NeoPTimal can be used in the laboratory as it gives results comparable to those obtained with STA-Neoplastine CI Plus. Besides, thanks to its ISI=1, it guarantees reporting a PT ratio equal to INR which avoids errors.

Standardization of Prothrombin Time/International Normalized Ratio (PT/INR).

The prothrombin time (PT) represents the most commonly used coagulation test in clinical laboratories. The PT is mathematically converted to the international normalized ratio (INR) for use in monitoring anticoagulant therapy with vitamin K antagonists such as warfarin in order to provide test results that are adjusted for thromboplastin and instrument used. The INR is created using two major PT 'correction factors', namely the mean normal PT (MNPT) and the international sensitivity index (ISI). Manufacturers of reagents and coagulometers have made some efforts to harmonizing INRs, for example, by tailoring reagents to specific coagulometers and provide associated ISI values. Thus, two types of ISIs may be generated, with one being a 'general' or 'generic' ISI and others being reagent/coagulometer-specific ISI values. Although these play a crucial role in improving INR results between laboratories, these laboratories reported INR values are known to still differ, even when laboratories use the same thromboplastin reagent and coagulometer. Moreover, ISI values for a specific thromboplastin can vary among different models of coagulometers from a manufacturer using the same method for clot identification. All these factors can be sources of error for INR reporting, which in turn can significantly affect patient management. In this narrative review, we provide some guidance to appropriate ISI verification/validation, which may help decrease the variability in cross laboratory reporting of INRs.

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

Objectives Frozen 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. Methods INRs 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. Results For 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. Conclusions Processing 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.

The rivaroxaban-adjusted normalized ratio: use of the prothrombin time to monitor the therapeutic effect of rivaroxaban

ABSTRACTBackground: The prothrombin time may be used to monitor the plasma concentration of rivaroxaban. However, there is variability in the responsiveness of rivaroxaban to different thromboplastins. We aimed to develop a rivaroxaban-monitoring method using the prothrombin time to reduce the differences in the sensitivity among reagents.Methods: Rivaroxaban-spiked pooled normal plasma at a 0–1000 ng/ml concentration was used to generate a rivaroxaban-adjusted sensitivity index (SI) values, and was tested with three thromboplastins. The warfarin-adjusted international sensitivity index (ISI-warfarin), rivaroxaban-adjusted sensitivity index (SI-rivaroxaban), international normalized ratio (INR) calculated with ISI-warfarin, normalized ratio (NR) calculated with SI-rivaroxaban, and their coefficient of variances (CVs) were compared. The NR-rivaroxaban value was compared with the results of an anti-Xa assay.Results: The ISI-warfarin and SI-rivaroxaban using different thromboplastins were 1.02 and 1.88, respectively, with Thromborel S, 0.90 and 1.00 using Recombiplastin 2G, and 1.30 and 1.15 using Neoplastin CI-plus. Between-thromboplastin variability expressed as CV were 6.3%–25.1% when expressed as INR-warfarin and 1.7%–4.7% when expressed as NR-rivaroxaban. CVs for the NR-rivaroxaban with another laboratory were significantly lower than those for INR-warfarin. Anti-Xa assay v NR-rivaroxaban correlation coefficients were 0.97–0.99.Conclusion: Using a rivaroxaban-specific NR effectively minimises inter-thromboplastin variability. By utilizing a NR-rivaroxaban, standardized prothrombin time results could be rapidly obtained, especially useful in standardizing the therapeutic effect of rivaroxaban.

How to Generate a More Accurate Laboratory-Based International Normalized Ratio: Solutions to Obtaining or Verifying the Mean Normal Prothrombin Time and International Sensitivity Index.

Although the landscape of anticoagulation therapy is evolving, vitamin K antagonists (VKAs) such as warfarin remain an anticoagulant of choice for many clinicians and their patients. Nevertheless, management of VKA therapy remains challenging, largely because of patient variability and drug and food interactions; thus, VKA dosing has to be personalized. This is achieved by regular monitoring using a test called the prothrombin time (PT), mathematically converted to an international normalized ratio (INR). The INR system is meant to harmonize laboratory test results by taking into account reagent and instrumentation variability that is otherwise expected to give rise to variable PT values, but which should accordingly lead to less variable INR values. Of clinical importance, too low an INR is suggestive of increased thrombotic risk and typically means the VKA dose should be increased, whereas too high an INR is suggestive of increased bleeding risk and typically means the VKA dose should be temporarily withheld and/or decreased. However, evidence continues to show that variability in INR values between laboratories remains unacceptably high. Given that modern instrumentation provides for robust analytical values-meaning highly reproducible intralaboratory clotting times or PTs in this case-the most likely cause of high INR variability is inconsistency in the INR test components-meaning the MNPT (mean normal PT) and ISI (international sensitivity index) values used by laboratories to generate a given INR. In other words, there are doubts as to the accuracy of some INR values because there are corresponding doubts about the accuracy of MNPT and/or ISI values that have been assigned by some laboratories for their reagent/instrument combination. The current report is intended to provide some solutions around the problems of inaccurate INRs, ISIs, and MNPTs, thus aiming to drive laboratory INRs closer to "truth," and thus promote better patient management. The novel strategies include a primary process of transference to obtain/verify MNPT and/or ISI values for a new reagent using an existing reagent as reference, and a secondary process whereby external quality assessment data can be used to correct bias or existing errors in assigned MNPT and/or ISI values.

Misguided by INR in Liver Disease Patients? Implications for Clinicians Including Pain Proceduralists.

THE ROSY PAST The prothrombin time (PT) assay, developed in 1935, was used in the identification of the anticoagulants dicumarol and warfarin. Currently, this assay is most commonly used to measure the therapeutic activity of warfarin. It was well known that PT results experienced a variation among centers using different reagents, making comparisons challenging. Around the same time came the invention of the international sensitivity index (ISI), allowing for calibration of different batches of thromboplastins to an international standard. To address interlaboratory PT variation, the international normalized ratio (INR), defined as the ratio of a patient’s PT to a control sample raised to the power of the ISI value, was invented in the 1980s. The INR became widely accepted after endorsement by the World Health Organization. This endorsement was only for control of oral anticoagulant therapy, as ISI calibration was specifically developed for comparing samples of patients with normal coagulation profiles to those who were anticoagulated with Coumadin (warfarin; Bristol-Myers-Squibb, New York, NY) for at least 6 weeks.1 Historically, plasma transfusions have been recommended for patients whose PT was found to be 1.5× longer than normal. Early thromboplastins in the United States had an ISI >2.0; therefore, a 1.5× increase in PT would equal an INR of 2.25. Currently, many thromboplastin reagents have an ISI close to 1.0 (World Health Organization standard); therefore, the same sample with a PT 1.5× longer than normal will equal an INR of 1.5. In the past, a PT 1.5× longer than normal indicated a moderate to severe factor deficiency (factor levels <30%), whereas today, the same value indicates only a mild factor deficiency (factor levels >40%).2 Figure 1.: The cascade model of fibrin formation. This model divides the coagulation system into separate redundant pathways (extrinsic and intrinsic) either of which can result in generation of FXa. The common pathway results in generation of thrombin and subsequent cleavage of fibrinogen to fibrin. Many of the enzymes and enzymatic complexes require Ca2+ and binding to active membrane surfaces (PL) for full activity. For simplicity, feedback activation of procofactors to cofactors and the many inhibitors of the various enzymes have been omitted. Reprinted with permission from Smith.4 Ca2+ indicates calcium; Fb, fibrin; Fg, fibrinogen; FXa, activated form of factor X; HMWK, high molecular weight kininogen; K, kallikrein; PK, prekallikrein; PL, active membrane surfaces; TF, tissue factor.

Performance Evaluation and Local International Sensitivity Index Verification Using Automated Coagulation Analyzer Coapresta 2000

Performance Evaluation and Local International Sensitivity Index Verification Using Automated Coagulation Analyzer Coapresta 2000

International collaborative study for the calibration of proposed International Standards for thromboplastin, rabbit, plain, and for thromboplastin, recombinant, human, plain

Background The availability of International Standards for thromboplastin is essential for the calibration of routine reagents and hence the calculation of the International Normalized Ratio (INR). Stocks of the current Fourth International Standards are running low. Candidate replacement materials have been prepared. This article describes the calibration of the proposed Fifth International Standards for thromboplastin, rabbit, plain (coded RBT/16) and for thromboplastin, recombinant, human, plain (coded rTF/16). Methods An international collaborative study was carried out for the assignment of International Sensitivity Indexes (ISIs) to the candidate materials, according to the World Health Organization (WHO) guidelines for thromboplastins and plasma used to control oral anticoagulant therapy with vitamin K antagonists. Results Results were obtained from 20 laboratories. In several cases, deviations from the ISI calibration model were observed, but the average INR deviation attributabled to the model was not greater than 10%. Only valid ISI assessments were used to calculate the mean ISI for each candidate. The mean ISI for RBT/16 was 1.21 (between-laboratory coefficient of variation [CV]: 4.6%), and the mean ISI for rTF/16 was 1.11 (between-laboratory CV: 5.7%). Conclusions The between-laboratory variation of the ISI for candidate material RBT/16 was similar to that of the Fourth International Standard (RBT/05), and the between-laboratory variation of the ISI for candidate material rTF/16 was slightly higher than that of the Fourth International Standard (rTF/09). The candidate materials have been accepted by WHO as the Fifth International Standards for thromboplastin, rabbit plain, and thromboplastin, recombinant, human, plain.

Simplified Method for Local Correction of System International Normalized Ratio.

International normalized ratio (INR) derivation is dependent on the international sensitivity index (ISI) of thromboplastin. It varies with instrument and reagents used. To evaluate the role of a correction factor in the derivation of INR. We studied prothrombin time (PT) and INR from patients using 3 thromboplastins of varying ISI values. The correction factor was applied to the observed INR to obtain a corrected INR. The difference between corrected INR and observed INR values varies from -0.8 through 0.96. Corrected INR is dependent on PT only. It can be applied to all patients irrespective of cause for elevated PT.

Impact of an Institutional Change in Prothrombin Time Methodology on INR and MELD Scores in Liver Transplant Evaluations.

Allocation of liver grafts based on the model for end-stage liver disease (MELD) has been questioned because the prothrombin time (PT) measurement in cirrhosis patients changes with different commercially available thromboplastin reagents due to variations in the international sensitivity index (ISI). Our hospital laboratory electively changed the thromboplastin used in the PT/INR from PT-HS (ISI of 1.464) to Recombiplastin (ISI of 0.870). Theoretically, this change may yield lower INR and MELD scores in cirrhosis patients at our institution and thus impact access to organs. 27 patients listed for liver transplant prior to change in thromboplastin (Cohort A) were compared to 36 patients listed after the change (Cohort B). Patients in Cohort A had a mean INR of 1.41 and mean MELD of 13.9 compared to Cohort B with a mean INR of 1.39 and mean MELD of 13.8. Student's t-tests showed no statistically significant difference in INR (p = 0.799) or MELD (p = 0.955) between cohorts. We expected overall INR and MELD scores to decrease following the change to a thromboplastin with a lower ISI. On the contrary, we found no evidence of a major trend in these values supporting the relative robustness of the MELD.

Accuracy of point of care coagulometers compared to reference laboratory measurements in patients on oral anticoagulation therapy

BackgroundVitamin K antagonists (VKA) are widely prescribed throughout the world. Patients on VKA therapy require international normalized ratio (INR) monitoring of venous blood to ensure the response remains within the therapeutic window. Point-of-care devices (POC-INR) can safely and easily monitor VKA efficacy but need to be evaluated in practice. The aim of this study was to assess the precision and accuracy of a new POC-INR (Qlab) compared to the laboratory plasma technique and the CoaguChek-XS system. MethodsConsecutive patients on VKA referred to our institution were included. The study was designed to analyze 75 patients divided equally in the following subgroups: INR<2; INR=2–3; INR>3. INR was measured with an established laboratory method (INRREF) with an international sensitivity index of 1.0 and by two different POC-INRs: the Qlab (INRQlab) and the CoaguChek-XS systems (INRXS). Results82 patients treated mainly for atrial fibrillation or venous thromboembolism disease were included. Precision in therapeutic range (INR=2–3) of both POC-INRs was satisfactory with a coefficient of variation of 4.6% for the Qlab and 4.3% for the CoaguChek-XS. INRRef was 2.70±1.36, INRQlab 2.59±1.25 and INRXS 2.89±1.37. Accuracy was low with the Qlab (R2=0.64) and higher with the CoaguChek-XS (R2=0.94). The mean relative difference from the INRRef was higher for the Qlab (18.4%) than for the CoaguChek-XS (12.9%). Clinical concordance was lower with the Qlab (78.2%) than with the CoaguChek-XS (90.0%). ConclusionThis study suggests that the Qlab has accuracy limitations with clinical consequences. New POC-INR devices require careful evaluation prior to clinical implementation.

Clinical usefulness of international normalized ratio calibration of prothrombin time in patients with chronic liver disease

The international normalized ratio (INR) may not be directly applicable to patients with liver disease. We aimed to establish an alternative INR calibration system for patients with liver disease and to evaluate the effect of their use in chronic liver disease patients. Eighty-two patients with liver cirrhosis (LC) were included, and their prothrombin times (PTs) were measured by using 5 commercial thromboplastins. Each of the thromboplastins was also assigned an international sensitivity index (ISIliver) by the plasmas from LC patients. INRvka, INRliver, model for end-stage liver disease (MELD)vka, MELDliver, Child-Pugh (Child)vka, and Childliver scores were calculated. The coefficient of variance of INRvka was significantly larger than that of INRliver (P<0.01). The mean difference in INRvka between the thromboplastins was also significantly larger than that in INRliver (P<0.01). The total mean MELDliver score was higher than the total mean MELDvka score. The mean difference between the MELDvka and MELDliver scores (MELD score≥15) was 3.2%. We reconfirmed that the use of the alternative calibration system described herein for patients with liver disease may resolve the variability of INR measurement. Our data suggest that we would need to reevaluate the correlation between Child-Pugh class, MELD score, and clinical prognosis by using INRliver for patients with LC.

Long-term stability of international standards for thromboplastin stored at -20 °C, -70 °C, and -150 °C

BackgroundLong-term stability is an essential requirement for all international biological standards. The main stocks of the current international standards for thromboplastin, i.e. RBT/05 (rabbit brain thromboplastin) and rTF/09 (recombinant human tissue factor), are stored at -20°C. The aim of the present study is to assess the long-term stability of the international sensitivity index (ISI) for RBT/05 and rTF/09. MethodsPart of the main stocks of RBT/05 and rTF/09 were stored at -70°C and -150°C, up to 38months. At various time points samples were taken from the materials stored at -20°C, -70°C, and -150°C. The samples were reconstituted and analysed in the prothrombin time (PT) test using plasma samples derived from healthy subjects and patients treated with vitamin K-antagonists (VKA). The PT’s obtained with the standards stored at -20°C were compared to the PT’s obtained with the standards stored at -70°C and at -150°C. The PT’s were used to calculate relative ISI values by means of orthogonal regression. ResultsThere were no important differences between the ISI values for the materials stored at -20°C, -70°C, and -150°C. There was no significant trend with storage time. ConclusionThe ISI values for the international standards RBT/05 and rTF/09 appear to be stable at storage temperatures of -20°C, -70°C, and -150°C.

Monitoring anticoagulant therapy with vitamin K antagonists in patients with antiphospholipid syndrome.

Because of the possible interference of antiphospholipid antibodies (APL) with the phospholipid component of thromboplastin reagents, concerns have been raised about the validity of international normalized ratio (INR) testing to monitor anticoagulant therapy with vitamin K antagonists in patients with antiphospholipid syndrome (APS). To investigate the reliability of the INR, we determined the INR using various prothrombin time (PT) assays and compared the results with those of a chromogenic factor X (CFX) assay. The study cohort consisted of 40 APS patients and 100 APL-negative patients who were on anticoagulant therapy for reasons other than APS. The agreement (i.e. the percentage of patients with a difference ≤0.5 INR units) between the PT-derived INR and CFX-derived INR equivalents was only moderate in both patient groups. The best agreement with CFX-derived INR equivalents was observed for the Thromborel S reagent in APS patients (69.1%) and for Neoplastin Plus in APL-negative patients (72.0%). Regarding the results for the point-of-care system CoaguChek XS, an agreement between the INR and the CFX-derived INR equivalent was less frequently observed in the APS patients (55.6 vs. 67.8%; p = 0.050). When considering all 3058 pairs of INR tests within the international sensitivity index (ISI)-calibrated range of 1.5 to 4.5s, we did not observe a higher variability of INR values in either the APS patient group or the subgroup of APS patients positive for lupus coagulants compared with the APL-negative controls. In conclusion, monitoring vitamin K antagonists (VKA) therapy with laboratory INR measurements seems to be suitable for the majority of APS patients.