European concerted action on anticoagulation. Quality assessment of the CoaguChek Mini and TAS PT-NC point-of-care whole-blood prothrombin time monitors

BACKGROUND: International Normalized Ratios (INRs) for prothrombin time obtained with the CoaguChek Mini and TAS (RapidPointCoag) PT-NC systems are markedly different and also differ from the "true" INR. There is therefore a need for local quality assessment (QA) of the two systems. METHODS: A set of 60 lyophilized artificially depleted and 60 lyophilized coumarin plasmas were tested at 10 centers on both point-of-care testing monitors. Subsets of three and five plasmas were selected as QA plasmas and compared with the remaining 55 to assess the relative ability of the systems to characterize performance at the individual centers. The incidence of aberrant results (outliers; >15% deviation from the true INR) was also recorded. The expected incidence with the QA plasmas was calculated and compared. RESULTS: On both systems, INR with the common sets of 55 lyophilized plasmas varied considerably between centers. With the TAS PT-NC, subsets of five and three European Concerted Action on Anticoagulation (ECAA) artificially depleted plasmas gave good correlation with the 55 plasmas, but the coumarin plasmas performed less well. With the CoaguChek Mini, correlation was good with sets of five artificially depleted QA plasmas and reasonable with three but was less satisfactory with the coumarin plasmas. Outliers were detected with both types of plasmas on both test systems but with variable success. CONCLUSIONS: With the TAS PT-NC, three ECAA artificially depleted lyophilized plasmas provided reliable QA, but five lyophilized coumarin plasmas were required. With the CoaguChek Mini, five artificially depleted plasmas gave reliable QA but coumarin plasmas gave poorer results. ECAA QA plasmas provide a local system for checking INRs obtained with monitors of both types.     

European Concerted Action on Anticoagulation. Evaluation of a method for International Sensitivity Index calibration of two point-of-care prothrombin time (PT) monitoring systems (CoaguChek Mini and TAS PT-NC) with fresh plasmas based on whole-blood equivalent PT

BACKGROUND: The International Sensitivity Index (ISI) calibration of whole-blood prothrombin time (PT) monitors for point-of-care testing (POCT) described by Tripodi et al. (Thromb Haemost 1993;70:921-4) has been shown to be dependable but is too complex and demanding. The use of plasma would simplify calibration of whole-blood POCT PT monitors, but important differences may exist between the ISI for whole blood and plasma calibrations. METHODS: In a 10-center calibration study of two POCT whole-blood monitoring systems (CoaguChek Mini and TAS PT-NC), we characterized the relationship between the log PT for whole blood and fresh plasma with use of single lots of test strips/cards. This relationship (linear) was used to correct the difference between the whole-blood and plasma ISI. The reliability of the correction with different lots of test strips/cards was assessed at three centers. The linear relationship was used to correct the difference in the whole-blood and plasma ISI with four other lots of TAS PT-NC cards and with two additional lots of CoaguChek Mini test strips. RESULTS: The correction decreased the ISI difference from 13.3% to 0.9% for the TAS PT-NC and from 5.7% to 0.6% for the CoaguChek Mini. In assessments at three centers, which included different lots of test strips/cards, the mean ISI difference was markedly decreased with the TAS PT-NC but not with the CoaguChek Mini, for which the mean ISI difference increased slightly. CONCLUSIONS: The proposed correction resolves the discrepancy between whole-blood and fresh plasma ISI calibrations with TAS PT-NC test cards. The CoaguChek Mini systems could be calibrated without this correction.     

Coagulometer international sensitivity index (ISI) derivation,a rapid method using the prothrombin time/international normalized ratio (PT/INR) Line: a multicenter study

Summary. Background: The original WHO procedure for prothrombin time (PT) standardization has been almost entirely abandoned because of the universal use of PT coagulometers. These often give different international normalized ratio (INR) results from the manual method, between individual makes of instruments and with instruments from the same manufacture. Method A simple procedure is required to derive local INR with coagulometers. The PT/INR Line method has recently been developed using five European Concerted Action on Anticoagulation (ECAA) certified plasmas to derive local INR. This procedure has been modified to derive a coagulometer PT/INR Line providing International Sensitivity Index (ISI) and mean normal PT (MNPT) for coagulometers and give local INR. Results have been compared with conventional ISI calibrations at the same laboratories. Results: With human thromboplastins, mean ISI by local calibration was 0.93 (range: 0.77–1.16). With the PT/INR Line, mean coagulometer ISI was higher, for example 0.99 (0.84–1.23) but using the PT/INR Line derived MNPT there was no difference in local INR. Between‐centre INR variation of a certified validation plasma was reduced with human and bovine reagents after correction with local ISI calibrations and the PT/INR Line. Conclusion: The PT/INR Line–ISI with its derived MNPT is shown to provide reliable local INR with the 13 different reagent/coagulometer combinations at the 28 centres in this international study.     

Guidelines on preparation, certification, and use of certified plasmas for ISI calibration and INR determination.

Reliable international normalized ratio (INR) determination depends on accurate values for international sensitivity index (ISI) and mean normal prothrombin time (MNPT). Local ISI calibration can be performed to obtain reliable INR. Alternatively, the laboratory may determine INR directly from a line relating local log(prothrombin time [PT]) to log(INR). This can be done by means of lyophilized or frozen plasmas to which certified values of PT or INR have been assigned. Currently there is one procedure for local calibration with certified plasmas which is a modification of the WHO method of ISI determination. In the other procedure, named 'direct' INR determination, certified plasmas are used to calculate a line relating log(PT) to log(INR). The number of certified plasmas for each procedure depends on the method of preparation and type of plasma. Lyophilization of plasma may induce variable effects on the INR, the magnitude of which depends on the type of thromboplastin used. Consequently, the manufacturer or supplier of certified plasmas must assign the values for different (reference) thromboplastins and validate the procedure for reliable ISI calibration or 'direct' INR determination. Certification of plasmas should be performed by at least three laboratories. Multiple values should be assigned if the differences between thromboplastin systems are greater than 10%. Testing of certified plasmas for ISI calibration may be performed in quadruplicate in the same working session. It is recommended to repeat the measurements on three sessions or days to control day-to-day variation. Testing of certified plasmas for 'direct' INR determination should be performed in at least three sessions or days. Correlation lines for ISI calibration and for 'direct' INR determination should be calculated by means of orthogonal regression. Quality assessment of the INR with certified plasmas should be performed regularly and should be repeated whenever there is a change in reagent batch or in instrument. Discrepant results obtained by users of certified plasmas should be reported to manufacturers or suppliers.     

The prothrombin time/international normalized ratio (PT/INR) Line: derivation of local INR with commercial thromboplastins and coagulometers – two independent studies

Summary. Background: The WHO scheme for prothrombin time (PT) standardization has been limited in application, because of its difficulties in implementation, particularly the need for mandatory manual PT testing and for local provision of thromboplastin international reference preparations (IRP). Methods: The value of a new simpler procedure to derive international normalized ratio (INR), the PT/INR Line, based on only five European Concerted Action on Anticoagulation (ECAA) calibrant plasmas certified by experienced centres has been assessed in two independent exercises using a range of commercial thromboplastins and coagulometers. INRs were compared with manual certified values with thromboplastin IRP from expert centres and in the second study also with INRs from local ISI calibrations. Results: In the first study with the PT/INR Line, 8.7% deviation from certified INRs was reduced to 1.1% with human reagents, and from 7.0% to 2.6% with rabbit reagents. In the second study, deviation was reduced from 11.2% to 0.4% with human reagents by both local ISI calibration and the PT/INR Line. With rabbit reagents, 10.4% deviation was reduced to 1.1% with both procedures; 4.9% deviation was reduced to 0.5% with bovine/combined reagents with local ISI calibrations and to 2.9% with the PT/INR Line. Mean INR dispersion was reduced with all thromboplastins and automated systems using the PT/INR Line. Conclusions: The procedure using the PT/INR Line provides reliable INR derivation without the need for WHO ISI calibration across the range of locally used commercial thromboplastins and automated PT systems included in two independent international studies.     

European concerted action on anticoagulation. Use of plasma samples to derive international sensitivity index for whole-blood prothrombin time monitors.

BACKGROUND: To simplify International Sensitivity Index (ISI) calibration, the possibility of substituting fresh plasma for fresh whole-blood samples with point-of-care testing (POCT) whole-blood monitors was investigated in a three-center study of three different POCT systems. METHODS: A modified full WHO calibration procedure based on 20 healthy controls and 60 coumarin-treated patients was performed on three monitoring systems with whole-blood and plasma samples against plasma tested using the European Concerted Action on Anticoagulation (ECAA) rabbit reference plain thromboplastin and the manual prothrombin time (PT) method. RESULTS: With one of the three systems, the mean ISI was 1.51 for whole blood and 1.49 for plasma; with the second system, the mean ISI was 1.08 for both whole blood and plasma. With the third system, however, the difference between the mean ISI for whole blood and that for plasma was greater (1.15 and 1.01, respectively). Overall, the precision of the calibrations was less than with traditional manual plasma PT testing. CONCLUSIONS: Provided that an appropriate calcium chloride concentration is used, the plasma PT results can be used for accurate ISI calibration of two of these three whole-blood POCT systems. Precision criteria need to be modified for POCT monitors.     

Comparison of local International Sensitivity Index calibration and ''Direct INR'' methods in correction of locally reported International Normalized Ratios: an international study

BACKGROUND: It is no longer feasible to check local International Normalized Ratios (INR) by the World Health Organization International Sensitivity Index (ISI) calibrations because the necessary manual prothrombin time technique required has generally been discarded. OBJECTIVES: An international collaborative study at 77 centers has compared local INR correction using the two alternative methods recommended in the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis guidelines: local ISI calibration and 'Direct INR'. METHODS: Success of INR correction by local ISI calibration and with Direct INR was assessed with a set of 27 certified lyophilized plasmas (20 from patients on warfarin and seven from normals). RESULTS: At 49 centers using human thromboplastins, 3.0% initial average local INR deviation from certified INR was reduced by local ISI calibration to 0.7%, and at 25 centers using rabbit reagents, from 15.9% to 7.5%. With a minority of commercial thromboplastins, mainly 'combined' rabbit reagents, INR correction was not achieved by local ISI calibration. However, when rabbit combined reagents were excluded the overall mean INR deviation after correction was reduced further to 3.9%. In contrast, with Direct INR, mean deviation using human thromboplastins increased from 3.0% to 6.6%, but there was some reduction with rabbit reagents from 15.9% to 10% (12.3% with combined reagents excluded). CONCLUSIONS: Local ISI calibration gave INR correction for the majority of PT systems but failed at the small number using combined rabbit reagents suggesting a need for a combined reference thromboplastin. Direct INR correction was disappointing but better than local ISI calibration with combined rabbit reagents. Interlaboratory variability was improved by both procedures with human reagents only.     

Quality assessment of CoaguChek point-of-care prothrombin time monitors: comparison of the European community-approved procedure and conventional external quality assessment

BACKGROUND: There is a need for dependable quality assessment (QA) of the widely used CoaguChek point-of-care testing prothrombin time monitor. By use of the prescribed set of 5 CoaguChek certified international normalized ratio (INR) QA plasmas, we compared the reliability of the immediate QA of individual monitors described in the European Community-recommended Technology Implementation Plan with conventional external QA analysis. METHODS: Experienced staff tested CoaguChek point-of-care monitors in routine use for controlling oral anticoagulant dosage at 9 Netherlands Thrombosis Service Centres. Testing was performed with both the certified CoaguChek INR for a set of 5 QA individual plasmas from the Eur Con Action on Anticoag (ECAA) and conventional external QA analysis. RESULTS: Patients brought 523 CoaguChek monitors to our service centers for assessment. The proportion with unsatisfactory performance indicated by a 15% deviation from the ECAA set was compared with 15% deviation from overall median INR of all CoaguChek monitors in the survey, as in conventional QA analysis. The results were similar (20.3% and 18.5%, respectively). Interlot differences of CoaguChek test strips were detected, but the incidence of unsatisfactory performance was similar with both analyses, from 6.5% to 37.5% with the certified INR method and from 5.9% to 33.3% with the overall median analysis. CONCLUSIONS: The results validate the use of the European Action on Anticoagulation rapid single-instrument QA-specific procedure for CoaguChek users compared with the nonspecific conventional QA analysis that relies on deviation from the overall median INR.     

A modified method of prothrombin time/International Normalised Ratio determination in capillary blood and monitoring oral anticoagulant therapy.

BACKGROUND: Oral anticoagulant therapy is monitored by a prothrombin time (PT) assay. The PT is standardised by the International Normalised Ratio (INR). The purpose of this study was to work out a modified method of PT/INR measurement in capillary blood for monitoring anticoagulation treatment. METHODS: Healthy donors, subjects with high or low haematocrit values, and oral anticoagulant-treated patients were included in the study. Plasma and capillary blood PT/INRs were determined by the standard Quick clotting assay, by the modified approach and with the CoaguChek S analyser. RESULTS: The performance characteristics of the developed method were accuracy, due to taking into account whole capillary blood haematocrit values, and precision, due to a decrease in the viscosity of the analysed samples. Implementation of the modified method showed that it is possible to use PT values of normal plasma for capillary blood INR calculation. The developed method allowed the determination of PT in capillary blood within the haematocrit value range from 0.15 up to 0.7. For capillary blood, the results of the modified method closely correlated with PT/INR values determined by the reference Quick method in venous plasma (r=0.99) and with the CoaguChek S analyser (r=0.97). CONCLUSIONS: The modified method of capillary blood PT/INR determination could be recommended for oral anticoagulant therapy monitoring.     

Modified capillary blood prothrombin-time test for the calculation of an international normalized ratio

Prothrombin time (PT) is usually measured in citrated venous blood. This test is undesirable in pediatric practice and in patients taking anticoagulants due to frequent venepunctures. Capillary blood PT test has no adverse impact. The authors have developed a standardized modified method for PT measurement in capillary blood. The adequacy of the test is due to the fact that analyzed test packed cell volumes are kept in mind. The modified test has shown that the values of normal plasma PT may be used to calculate an international normalized ratio (INR). It makes it possible to determine capillary blood PT in the range of packed cell volumes from 0.15 to 0.7 in the examinees and to monitor anticoagulant therapy. The results of the modified test closely correlated with those when determining PT and INR in venous plasma (r = 0.99) and applying the CoaguChek test (r = 0.97).     

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.     

Use of lyophilized calibrant plasmas for simplified international normalized ratio determination with a human tissue factor thromboplastin reagent derived from cultured human cells

BACKGROUND: For monitoring of treatment with oral anticoagulants, the clotting time obtained in the prothrombin time (PT) test is transformed to the International Normalized Ratio (INR) with use of a system-specific International Sensitivity Index (ISI). The calibrant plasma procedure (CPP) is an alternative approach to INR calculation based on the use of a set of lyophilized plasmas with assigned INRs. METHODS: With the CPP, a linear relationship is established between log(PT) and log(INR), using orthogonal regression. CPP was validated for Simplastin HTF, a new human tissue factor reagent derived from cultured human cells. CPP precision was assessed as the CV of the slope of the regression line. The accuracy of the CPP was determined by comparing the INR obtained with the CPP with that obtained with the established ISI-based reference method. INRs of the calibrants were assigned by different routes: by manufacturer (consensus labeling) or by use of Simplastin HTF or International Reference Preparations (IRPs; rTF/95 or RBT/90). RESULTS: The mean CV of the CPP regression slope ranged from 1.0% (Simplastin HTF reagent-specific INR) to 2.4% (INR assigned with rTF/95). INRs calculated with the CPP were similar to those obtained with the reference method, but when the routes for assigning INRs to the calibrant plasmas were compared, the mean difference in INR between CPP and the reference method was smaller with Simplastin HTF reagent-specific values. In several (but not all) cases, this difference was significant (P <0.05, t-test). CONCLUSION: CPP can be used for local INR determination, but better precision and accuracy are obtained with reagent-specific INRs compared with INR assignment by consensus labeling or IRP.     

凝血活酶敏感指数对凝血酶原时间测定的影响

本文观察了四种不同国际敏感指数的凝血活酶试剂，在相同条件下，对２５例正常人和５０例口服华法令病人进行了ＰＴ测定，结果显示正常参考值随所用凝血活酶的ＩＳＩ不同而异。建议各实验室应依其所用试剂建立自己实验室的正常参考值。对口服抗凝药的５０例患者测得ＰＴｓ（秒）和ＰＴＲ（比率）经方差分析，四组结果有显著性差异（Ｐ〈０．０１），而按ＩＮＲ＝ＰＴＲ＾ＩＳＩ换算成国际标准化比率（ＩＮＲ）后，经方差分析，四组Ｉ     

凝血酶原时间ISI/INR系统测定中的一些问题及改进意见

目的对凝血酶原时间(PT)测定ISI/INR系统出现的一些问题提出相应的改进建议。方法对上海市12家医院在用的仪器和匹配的PT试剂,对日常使用的正常血浆平均凝血酶原时间(MNPT)作调研实测,将结果进行分析;调查试剂的仪器特定(spec ific)国际敏感度指数(ISI)值与世界卫生组织(WHO)的手工法ISI定标值之间的差异;用2种已知国际标准化比值(INR)的异常参比血浆代替WHO的ISI系统作质控并行比较。结果12家中有4家日常使用的平均正常凝血酶原时间(MNPT)明显偏离实测值,分别为0.8、0.9、1.0和1.8 s。用WHO CRM149R参比,用手工法标定的凝血活酶和109 mmol枸橼酸钠抗凝的不同PT值血标本,在Sysm ex1500型、C.2000型仪器上测定试剂的仪器特定ISI,其结果比手工法分别减少4.1%和4.7%,但采用HEPES-枸橼酸钠抗凝剂标本时,2种型号仪器的特定ISI比手工法分别减少16.7%及7.7%。用已知INR异常参比血浆,国产品与进口品对照的结果良好。结论受调研12家中,有4家血凝分析仪器调研时实测的MNPT明显偏离日常使用值。有几家医院试剂的仪器特定ISI值也存在问题,建议纠正。用已知INR异常参比血浆代替WHO手工法标定凝血活酶ISI法作质控,使用简便,又不需MNPT参数,值得推广。     

血浆凝血酶原时间测定中建立仪器区域国际敏感指数的实验探讨

目的　探讨临床口服抗凝治疗时血浆凝血酶原时间 (PT)监测的标准化 ,为临床提供比较准确的PT 国际标准化比值 (PT INR)结果。方法　使用PT INR校准血浆建立PT测定试剂在不同仪器上的区域性国际敏感度指数 (LocalISI) ,以此对新鲜血浆进行PT测定。结果　未经LocalISI校准的PT试剂测定血浆的PT时 ,INR结果差异较大 (P <0 .0 1)。试剂经LocalISI校准后 ,测定血浆PT时 ,INR结果良好 (P >0 .0 5及Kap pa >0 .75 )。 结论　在PT测定时 ,只要建立仪器和测定试剂的LocalISI ,INR结果就具有较好的一致性。     

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.     

Properties of recombinant human thromboplastin that determine the International Sensitivity Index (ISI)

Prothrombin Time (PT) clotting tests are widely used to monitor oral anticoagulation therapy and to screen for clotting factor deficiencies. The active ingredient in PT reagents (thromboplastins) is tissue factor, the integral membrane protein that triggers the clotting cascade through the extrinsic pathway. Several years ago, a system for calibrating and using thromboplastin reagents, known as the International Sensitivity Index (ISI) and the International Normalized Ratio (INR), was developed to standardize monitoring of oral anticoagulant therapy. The ISI/INR method, while revolutionizing the monitoring of coumarin therapy, has been criticized for a number of perceived shortcomings. We have undertaken a series of studies aimed at achieving a detailed understanding of which parameters influence the ISI values of thromboplastin reagents, with an ultimate goal of creating 'designer thromboplastins' whose sensitivities to the various clotting factors can be individually tailored. In this study, we demonstrate that ISI values of thromboplastin reagents based on relipidated, recombinant human tissue factor can be controlled by a combination of changes in the phospholipid content (in particular, the levels of phosphatidylserine and phosphatidylethanolamine) and ionic strength. The sensitivity of a given thromboplastin reagent can be increased (i.e. its ISI value decreased) by decreasing the content of phosphatidylserine and/or increasing the ionic strength. The molar ratio of phospholipid to tissue factor, on the other hand, had essentially no impact on ISI value.     

A comparison of INRs after local calibration of thromboplastin international sensitivity indexes.

There are approximately 300 reagent/instrument combinations for performing prothrombin times/international normalized ratios (PT/INR) in the United States. Manufacturers and laboratories continually struggle to ensure that the International Sensitivity Index (ISI) of their thromboplastin is accurate for assaying PT/INR. OBJECTIVE: This study reports the feasibility of a new method to locally calibrate ISI of thromboplastin using the mechanical STA automated coagulation analyzer (Diagnostica-Stago Inc.) and two photo-optic coagulation analyzers, the BCS (Dade-Behring) and CA-540 (Sysmex). DESIGN: Neoplastine CI+ (CI+) (Diagnostica-Stago Inc); Thromboplastin C+ (TC+); Thromborel S (TRS); and Innovin (I) (Dade-Behring) were used in this study. A mean normal PT (MNPT) was determined for each reagent/instrument combination using samples from 25 normal individuals. Manufacturer instrument specific ISI values were not available for the STA with TC+, TRS and I. The CA540 had no ISI value for CI+ and the BCS system had no manufacturer assigned ISI values for TC+ and I; generic photo-optic and mechanical ISI manufacturer values were used for these two systems. Local on-site calibration was performed using frozen plasma calibrators to determine ISI values for each thromboplastin. Post-calibration, 95 patient samples were assayed for each reagent/instrument system combination using the manufacturer ISI and the local calibrated ISI to determine the INR result. PATIENTS: Patients from whom samples were obtained included five with a lupus anticoagulant, 30 on heparin therapy, and 60 on coumadin therapy. RESULTS: Differences between manufacturer versus local calibrated ISI ranged from 0.9% to 18.9% for normal sample INRs and from 0.8% to 16.4% for patient sample INRs. The number (or proportion) of patient specimens with clinically significantly different INR values (>10.0% difference) ranged from zero for several reagent combinations to more than half (or >50.0%) of those tested for several other combinations. CONCLUSION: Our results indicated that by locally calibrating ISI values, each laboratory may eliminate variability and guesswork between different reagent/instrument systems for ISI values when performing PT/INR assays and potentially improve the clinical accuracy of their patients' PT/INR results.     

The agreement between capillary and venous sampling for plasma PT/INR results

Abstract

Regular measurement of prothrombin time (PT) as an international normalized ratio (INR) is of great importance in ensuring a safe Warfarin treatment due to the narrow therapeutic range. Hence, accurate results of the PT/INR analysis are crucial. Due to the high sampling load that patients on Warfarin experience, some prefer capillary sampling (from the tip of the finger) as an alternative to standard venous sampling (from the cubital fossa). The present study evaluated the method of capillary sampling compared to the standard venous method for plasma PT/INR measurement. Both venous and capillary samples were collected simultaneously for plasma PT/INR testing from 100 patients of which the majority undergoing active Warfarin treatment. The samples were analyzed on a Sysmex 2100i instrument (Siemens) using the Owrens method with PT reagents from MediRox. The capillary sampling method showed statistically significant lower values (p?相似文献   

Effect of coagulation factors on discrepancies in International Normalized Ratio results between instruments

Abstract Background: The reasons for discrepancies between International Normalized Ratio (INR) results determined by point-of-care-instruments and laboratory measurements are not fully understood. In this study we investigated whether different levels of coagulation factors in the plasma of patients can explain some of the systematic and/or random parts of the difference in INR between the instruments. Methods: Blood samples were collected at four different patient visits from each of 34 outpatients on warfarin treatment. INR was determined on a laboratory instrument (STA Compact?) and on three point-of-care instruments (Simple Simon?PT, CoaguChek?XS and INRatio?). In addition, the level of fibrinogen, coagulation factors II, V, VII and X was determined. INR instruments were compared in pairs. Simple linear regressions as well as multiple linear regressions and nested ANOVA analyses were used to examine the data. Results: The coagulation factors, especially fibrinogen, factors II and VII, could explain between 16% and 45% of the total variance of the differences in INR between instruments dependent on instruments compared. After correction for factors no systematic difference was seen for four of the six comparisons and the between- and within-subject variation of the differences were reduced by up to 69% and 52%, respectively. Conclusions: By correcting for the appropriate coagulation factors, especially the systematic differences, but also the between- and within-subject variation of the differences between instruments, were reduced. This indicates that different levels of coagulation factors in the plasma of the patients play an important role in explaining discrepancies between INR instruments.