European Concerted Action On Anticoagulation Research Articles

Establishing an external quality assessment scheme for point-of-care international normalized ratio in Thailand.

Effective warfarin therapy management has gained national interest, resulting in the increased use of point-of-care testing (POCT) for international normalized ratio (INR). External quality assessment (EQA) is recommended to ensure quality of the testing. CoaguChek XS and CoaguChek XS Plus are the only commonly available POCT INR monitors in Thailand. Therefore, Thailand NEQAS for Blood Coagulation initiated the scheme for POCT INR in 2013, including only hospitals using these devices. Questionnaires were sent to the hospitals, enquiring about their interest in EQA participation. Two surveys were distributed; each included five certified European Concerted Action on Anticoagulation (ECAA) INR plasma sets. Unsatisfactory performance was indicated by a 15% deviation from the certified mean INR value. There were 156 hospitals using the devices. Thirty-five hospitals responded to the questionnaires. Medical personnel undertaking POCT INR were limited to laboratory staff in 29 (83%) of these centers, and 31 hospitals actually participated. The medians of results from participants were the same or nearly the same as the certified mean INRs. External quality assessment for POCT INR in Thailand is feasible using the ECAA plasmas as control materials. The results therefore appear encouraging to other developing countries to establish their own EQA schemes.

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

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. 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. 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. 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.

Evaluation of European Concerted Action on Anticoagulation Lyophilized Plasmas for INR Derivation Using the PT/INR Line

The prothrombin time/international normalized ratio (PT/INR) Line method based on 5 certified European Concerted Action on Anticoagulation (ECAA) plasmas provides reliable local INR values without conventional World Health Organization international sensitivity index calibrations. The present study investigated the use of different numbers and types of ECAA calibrant plasmas to derive accurate PT/INR Lines and reliable INR values. The numbers ranged from 3 to 10 plasmas in a set with normal or abnormal samples. Sets were selected, and sampling was repeated 1,000 times for each center to derive PT/INR Lines. The lines were selected randomly or from clusters. The INR values of 5 independent "validation" plasmas were compared before and after correction. In 56 calibrations, 5 ECAA plasmas gave better results than did fewer plasmas. Plasmas with wide-ranging INR values gave better results than randomly selected sets, and including a normal plasma was not essential. The INR deviations of validation plasmas from certified values were reduced with sets of human, bovine/combined, and rabbit reagents. Deviations of more than 10% from certified INR values were significantly reduced (P < .001).

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

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). 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. 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. 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.

Simplified Method for International Normalized Ratio (INR) Derivation Based on the Prothrombin Time/INR Line: An International Study

The need to perform local International Sensitivity Index (ISI) calibrations and in particular the requirement for a manual method for prothrombin time (PT) determination, have proved to be obstacles to application of the WHO scheme for PT standardization. We used international normalized ratio (INR) derived with a set of only 5 European Concerted Action on Anticoagulation (ECAA) lyophilized calibrant plasmas, certified manually by expert centers with reference thromboplastins, to determine a local PT/INR Line. We compared results of an independent set of validation plasmas with INRs from conventional ISI calibrations and with manually certified INRs. The mean certified INR of 5 lyophilized validation plasmas was 2.41 with human thromboplastin, 2.04 with bovine/combined, and 2.80 with rabbit. With 42 human reagents, the mean observed INR of the validation plasmas was 2.68 (11.2% deviation from certified INR). Deviation was reduced to 0.4% with both local ISI calibration and the PT/INR Line. Eight results based on bovine/combined thromboplastin gave an INR deviation of 4.9%, becoming 0.5% after ISI calibration and 2.4% with the PT/INR Line. Six results with rabbit reagents deviated from certified INR by 2.5%. After ISI calibration, deviation became 1.1%, and with the PT/INR Line, 0.7%. The PT/INR Line gave similar results with both linear and orthogonal regression analysis. The total proportion of validation plasmas giving INR within 10% deviation from certified values was 42.5% with uncorrected INR, which increased to 92.1% with local ISI calibration and 93.2% with the PT/INR Line. The PT/INR Line procedure with 5 ECAA calibrant plasmas successfully substitutes for local ISI calibrations in deriving reliable INRs.

External quality assessment (EQA) for CoaguChek monitors

Anticoagulant control facilities are being overwhelmed by requests for monitoring and large numbers of patients are not therefore receiving treatment. Procedures designed for point-of-care testing have therefore been developed, the most popular being the CoaguChek. The need for external quality assessment (EQA) of monitors used by patients in self-management has been stressed in a European Commission (EC) Directive. It would not however be feasible for all CoaguChek monitors to be enrolled in national or regional EQA schemes which take time to organise and analyse. The European Concerted Action on Anticoagulation (ECAA) has therefore evolved a simpler system. Its value has been assessed in collaboration with the European Concerted Action on Thrombosis (ECAT). 523 monitors were tested at nine clinics which asked patients to bring their CoaguChek instruments to be assessed with the ECAA/ECAT procedure based on a set of 5 plasma samples with certified international normalised ratios (INR). 15% or more deviation from the certified INR on a single certified plasma sample from the set was defined by the ECAA as the limit of acceptable performance. One hundred and six (20.3%) of the monitors tested showed significant deviation and higher than average incidence of significant INR deviations reported with one specific numbered lot of test strips. Recent ECAA/ECAT, Danish and Italian studies report regular EQA of CoaguChek monitors is essential. There is general agreement that this should be performed at reasonably frequent intervals, at six months or whenever there is a change of the manufacturer's test strips.

The authors of the article cited above respond:

The European Concerted Action on Anticoagulation (ECAA) includes the founder and former long-term organizer of the UK National External Quality Assessment Scheme (NEQAS) and the WHO International External Quality Assessment Scheme in blood coagulation as well as current European national external quality assessment (EQA) organizers. We strongly endorse the 2 main points made by Kitchen and his UK NEQAS colleagues, that EQA for point-of-care international normalized ratio (INR) devices should be mandatory and caution is required when interpreting data from lyophilized plasma samples analyzed with whole blood prothrombin time (PT) monitors. During the past several years, the ECAA and its successor, European Action on Anticoagulation (EAA), have published data on both of these concerns in more than 60 reports, including 4 in Clinical Chemistry . With regard to plasma/whole blood differences, the ECAA initially studied the reliability of use of plasma samples in calibrating the CoaguChek monitor (1) with an international sensitivity index (ISI). An optimum formulation of …

European Concerted Action on Anticoagulation (ECAA): an assessment of a method for ISI calibration of two whole blood point-of-care PT monitor systems based on lyophilized plasmas using whole blood equivalent PT

Previously, the attempt to simplify the International Sensitivity Index (ISI) calibration of the CoaguChek Mini whole blood point-of-care test prothrombin time (PT) monitor system was successful using lyophilized plasmas from coumarin-treated patients but not with lyophilized artificially depleted plasmas. With the TAS PT-NC monitor system, both types of plasma failed to provide reliable calibrations. The present study assesses a procedure for the ISI calibration of a TAS PT-NC and CoaguChek Mini whole blood point-of-care test PT monitor systems using lyophilized plasmas. Using lyophilized artificially depleted and coumarin plasma calibrations, we have evaluated a correction for the monitor displayed PT. This was based on a 'line of equivalence' derived from the relationship between whole blood and fresh plasma PT with both types of monitor system. With the TAS PT-NC, the use of this 'line of equivalence' resulted in reliable ISI with both lyophilized coumarin and artificially depleted plasmas. There was no significant difference between mean monitor and mean reference International Normalized Ratio (INR) with the artificially depleted plasmas. With the lyophilized coumarin plasma calibrations there was only a small INR difference. Correction with the 'line of equivalence' therefore facilitates calibration of the TAS PT-NC with lyophilized plasmas. With the CoaguChek Mini, the correction based on the 'line of equivalence' did not improve results but was not required with this system.

European Concerted Action on Anticoagulation (ECAA). An assessment of lyophilised plasmas for ISI calibration of CoaguChek and TAS whole blood prothrombin time monitors

Aims: The recommended method for the international sensitivity index (ISI) calibration of whole blood point of care testing (POCT) prothrombin time (PT) systems was originally described by Tripodi et al...

European concerted action on anticoagulation. Minimum numbers of lyophilized plasma samples for ISI calibration of CoaguChek and TAS point-of-care whole blood prothrombin time monitors.

International sensitivity index (ISI) calibration of whole blood prothrombin time (PT) monitors is too complex. We previously simplified the method by using European Concerted Action on Anticoagulation (ECAA) lyophilized plasma samples with the TAS PT-NC (Bayer AG, Leverkusen, Germany) and the CoaguChek Mini (Roche Diagnostics, Mannheim, Germany) whole blood PT monitoring systems. The TAS PT-NC required a correction derived from the line of equivalence. Monte Carlo bootstrap analysis of reducing numbers of test samples was performed with both systems. Plasma samples from patients receiving coumarin (coumarin samples), healthy subjects (normal samples), and plasma samples artificially depleted of coagulation factors were used. With the TAS PT-NC, 20 coumarin samples or 20 artificially depleted samples with 7 normal samples gave reliable ISI and international normalized ratio and satisfactory precision. With the CoaguChek Mini, 30 coumarin and 10 normal samples were required. Simplification of ISI calibration of the 2 monitoring systems is possible using fewer ECAA lyophilized plasma samples than the 80 required according to the World Health Organization guidelines for conventional PT systems and previously recommended for fresh plasma samples tested on the same 2 monitoring systems.

European Concerted Action on Anticoagulation

International sensitivity index (ISI) calibration of whole blood prothrombin time (PT) monitors is too complex. We previously simplified the method by using European Concerted Action on Anticoagulation (ECAA) lyophilized plasma samples with the TAS PT-NC (Bayer AG, Leverkusen, Germany) and the CoaguChek Mini (Roche Diagnostics, Mannheim, Germany) whole blood PT monitoring systems. The TAS PT-NC required a correction derived from the line of equivalence. Monte Carlo bootstrap analysis of reducing numbers of test samples was performed with both systems. Plasma samples from patients receiving coumarin (coumarin samples), healthy subjects (normal samples), and plasma samples artificially depleted of coagulation factors were used. With the TAS PT-NC, 20 coumarin samples or 20 artificially depleted samples with 7 normal samples gave reliable ISI and international normalized ratio and satisfactory precision. With the CoaguChek Mini, 30 coumarin and 10 normal samples were required. Simplification of ISI calibration of the 2 monitoring systems is possible using fewer ECAA lyophilized plasma samples than the 80 required according to the World Health Organization guidelines for conventional PT systems and previously recommended for fresh plasma samples tested on the same 2 monitoring systems.

European Concerted Action on Anticoagulation (ECAA). Minimum number of centres for reliable International Sensitivity Index calibration of CoaguChek and TAS point-of-care whole blood monitors

Introduction: Prothrombin time (PT) test systems require multicentre calibration for reliable International Sensitivity Index (ISI). Multicentre calibration of CoaguChek Mini and TAS PT-NC point-of-care test (POCT) systems is less precise than conventional PT testing. The aim of the present study was to determine the number of centres required to give reliable ISI and International Normalised Ratio (INR) with these two POCT whole blood PT monitors. Materials and methods: A simulation study, based on results of a 10-centre calibration exercise, was performed to assess reliability of ISI and INR when the number of centres was reduced from 10 to 2. Results and Conclusions: With both systems, the range of ISI and INR deviation increased as the number of centres was reduced. For the CoaguChek Mini, at least five centres were needed for satisfactory INR deviation in 95% of calibrations. With the TAS PT-NC, three centres gave satisfactory INR at this level. The number of centres required for multicentre calibration of these two POCT PT systems is greater than the two proposed by World Health Organisation (WHO) Guidelines for conventional PT testing.

European Concerted Action on Anticoagulation (ECAA): multicentre international sensitivity index calibration of two types of point‐of‐care prothrombin time monitor systems

A multicentre modified World Health Organization (WHO)-type international sensitivity index (ISI) calibration has been performed at 10 European Concerted Action on Anticoagulation (ECAA) national laboratories using non-citrated whole-blood on two point-of-care test (POCT) prothrombin time (PT) monitor systems, CoaguChek Mini and TAS PT-NC, using single lots of test cards/strips. The relevant species (human and rabbit) WHO international reference preparations (IRPs) were tested with the manual PT technique on citrated plasma from the same blood donations. The ISI was calculated from the slope of the orthogonal regression line relating log PT (POCT) to log PT (IRP). The mean ISI of the CoaguChek Mini system was 1.75 and 1.13 with the prothrombin time non-citrated Thrombolytic Assessment System (TAS PT-NC). With the CoaguChek Mini system, seven out of 10 calibrations exceeded the current 3% WHO recommended limit for the coefficient of variation (CV) of the slope with conventional PT testing, whereas with the TAS PT-NC system, it was eight out of 10. All the POCT calibrations had a CV of the slope <5%. It is suggested that this level of precision be adopted as the limit of acceptability of calibration of these monitor systems. In these circumstances, the modified WHO-type ISI calibration appeared to be satisfactory for the POCT whole-blood monitors.

European Concerted Action on Anticoagulation. Use of Plasma Samples to Derive International Sensitivity Index for Whole-Blood Prothrombin Time Monitors

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. 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. 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. 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.

European Concerted Action on Anticoagulation (ECAA): International Normalized Ratio Variability of CoaguChek and TAS Point-of-Care Testing Whole Blood Prothrombin Time Monitors

The object was to assess the variability in displayed International Normalised Ratio (INR) between monitors of the same manufacture using whole blood samples from the same subjects. Two brands of monitor, CoaguChek Mini and the TAS PT-NC were tested. 14 instruments of each brand were tested on the same day at the same laboratory by the same operator using identical blood samples to avoid between-centre differences in samples and operator technique. Whole blood samples from two normal donors and four coumarin-treated patients were tested to assess between-instrument variability of INR. Results have been coded. There was a much wider dispersion of INR on Brand B than on Brand A. One Brand A instrument failed to give a result with one of the two whole blood samples from one patient. One Brand B monitor gave an aberrant result with one of the samples from a normal subject. On both brands of monitor, INR variability appeared to be due mainly to duplication differences rather than between-instrument variability on both normal and coumarin whole blood samples.

Minimum lyophilized plasma requirement for ISI calibration. European Concerted Action on Anticoagulation.

The minimum requirement of lyophilized plasma samples for a reliable International Sensitivity Index (ISI) was assessed by calibrations based on reducing numbers from a maximum of 60 depleted and 20 plasma samples from patients receiving coumarin using a manual technique and low ISI thromboplastin. The probability of achieving an international normalized ratio (INR) result within a clinically important range of 20% deviation has been assessed at European Concerted Action on Anticoagulation (ECAA) national laboratories in calibrations of ECAA reference thromboplastin against the certified prothrombin time (PT) with a reference thromboplastin. With conventional orthogonal regression using a certified PT and linear regression using certified INR, deviations and the coefficient of variation of the calibration slope increased with reduced numbers. The INR deviations became marked when the number of abnormal plasma samples was reduced to fewer than 20. Calibrations of 3 abnormal plasma samples and 1 lyophilized normal plasma sample gave a high incidence of deviations greater than 10% with an INR of 3.0. The study demonstrates that with both methods of analysis, an optimum minimum number of lyophilized plasma samples is needed for a reliable local ISI.

The European Concerted Action on Anticoagulation (ECAA) Evaluation of a Set of Lyophilized Normal Plasmas to Establish the Normal Prothrombin Time for Coagulometer Systems

Establishing the mean normal prothrombin time (MNPT) from fresh samples for prothrombin ratios and INR often presents difficulty in selection and collection of donors. A set of seven lyophilized normal plasmas has therefore been prepared at the ECAA Central Facility and studied at 143 laboratories in sixteen European states using coagulometers in serial field exercises. All centres tested either the high ISI ECAA rabbit or low ISI ECAA human reference thromboplastin. The MNPT of fresh plasmas and means of the lyophilized samples were closely comparable with most routine rabbit thromboplastins. Using human thromboplastins means with the lyophilized normals were marginally but significantly longer and with the bovine Thrombotest significantly shorter than the MNPT of fresh plasmas causing alterations in INR. There was no appreciable effect on INR of 2.5 and 3.5 when lyophilized normals were substituted for fresh normals with the rabbit reagents.

European Concerted Action on Anticoagulation (ECAA) - The Multicentre Calibration of Rabbit and Human ECAA Reference Thromboplastins

SummaryTwo candidate ECAA reference preparations have been calibrated in a multicentre exercise at 14 representative national laboratories to provide reference thromboplastin for a large field study in 16 European countries. Two preparations were required because of the established differences in ISI arising from the two main routes of calibration via rabbit and human IRP. To be comparable with working reagents in everyday use a human plain recombinant reagent of low ISI and a rabbit plain preparation of moderately high ISI were selected. A precise calibration of the two candidate preparations has been achieved with the manual PT technique and an ISI of 0.95 (SE 0.0078) for the human reagent and 1.67 (SE 0.0322) for the rabbit reagent.