| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH |
|
|
|
|||||||
|
|||||||||
Electronic Letters to:
|
Electronic letters published:
![[Read eLetter]](/icons/misc/sectionDOWN.gif){kind=icon}
Quality Assessment of CoaguChek Point-of-Care Prothrombin Time Monitors
Re: Quality Assessment of CoaguChek Point-of-Care Prothrombin Time Monitors
Comment on the article of Poller et al. in Clinical Chemistry 52:10 1843-1847 (2006)
|
|
|||
|
Siegmund L. Braun, Dr.med. Institut für Laboratoriumsmedizin, Deutsches Herzzentrum München, for the German Association of Selfmanagement of Anticoagulation (ASA e.V.)
Send letter to journal:
braun{at}dhm.mhn.de Siegmund L. Braun, et al.
|
To the editor: We read with interest the paper that appeared in this journal by Poller et al (1) in which they state that “The value and safety of this otherwise attractive approach to oral anticoagulant control by CoaguChek point-of-care testing could be greatly improved by combining it with the ECAA-recommended procedure for QA”. In our view the design of the study of Poller et al does not allow this conclusion, because: 1. CoaguChek is a prothrombin time monitor for use with whole blood without any anticoagulant added (see package insert of the manufacturer). It has to be emphasized that lyophilized plasma sample is not the intended sample for this system. The dried reaction mixture of the CoaguChek test strip does not contain calcium, therefore calcium chloride had to be added in a separate step in the procedure applied in this paper to facilitate clotting in the test. Therefore any statements and conclusions of Poller et al have to be restricted to the use of lyophilized plasma samples on the CoaguChek system. The test strip lot 965 is referred to by Poller et al as the lot giving more unsatisfactory results (24.6% of monitors) than all other lots combined. Obviously lot 965 does not meet the "certified" INR value when using the lyophilized ECAA plasma samples. Unfortunately the investigation of Poller et al did not include whole blood as sample material. Therefore we do not agree with the general statement of unsatisfactory results using this particular lot of test strips. As is generally known, no ideal quality control material has yet been developed that comes up to fresh liquid blood without anticoagulants. 2. The performance of the CoaguChek system in the hands of patients when using their own whole blood samples is not truly reflected by this investigation. In our opinion, an alternative quality assessment using the split-sample procedure is much more appropriate, where parallel to the measurement of the INR using the patient’s CoaguChek and a second CoaguChek also a venous blood sample is drawn and immediately analyzed by use of a standard laboratory method controlled by proficiency testing. A study by Solvik et al (2) showed that the split sample model is indeed an acceptable approach. We think that this procedure is more appropriate to detect suspected problems with individual monitors and test strip lots. Moreover, the reliability of INR results obtained with the CoaguChek system using whole blood has been proven in several other investigations (3-6) and the recently published meta-analysis by Heneghan (7) confirms the benefit patients gain by INR-self-management. 1. Poller L, Keown M, Ibrahim SA, van der Meer FJM, van den Besselaar AMHP, Tripodi A, et al. Quality Assessment of CoaguChek Point-of-Care Prothrombin Time Monitors: Comparison of the European Community-Approved Procedure and Conventional External Quality Assessment. Clin Chem 2006;52:1843-7. 2. Solvik US, A. Christensen, NG. Sandberg, S. External quality assessment of prothrombin time: the split sample model compared with external quality assessment with commercial control material. Scand J Clin Lab Invest 2006;66:337-49. 3. van den Besselaar AM, Breddin K, Lutze G, Parker-Williams J, Taborski U, Vogel G, et al. Multicenter evaluation of a new capillary blood prothrombin time monitoring system. Blood Coagulation and Fibrinolysis: An International Journal In Haemostasis And Thrombosis 1995;6:726-32. 4. Douketis JD, Lane A, Milne J, Ginsberg JS. Accuracy of a portable International Normalization Ratio monitor in outpatients receiving long-term oral anticoagulant therapy: comparison with a laboratory reference standard using clinically relevant criteria for agreement. Thrombosis Research 1998;92:11-7. 5. Shiach CR, Campbell B, Poller L, Keown M, Chauhan N. Reliability of point-of-care prothrombin time testing in a community clinic: a randomized crossover comparison with hospital laboratory testing. British Journal of Haematology 2002;119:370-5. 6. Jackson SL, Bereznicki LR, Peterson GM, Marsden KA, Jupe DML, Tegg E, et al. Accuracy, reproducibility and clinical utility of the CoaguChek S portable international normalized ratio monitor in an outpatient anticoagulation clinic. Clinical and Laboratory Haematology 2004;26:49-55. 7. Heneghan C, Alonso-Coello P, Garcia-Alamino J, Perera R, Meats E, Glasziou P. Self-monitoring of oral anticoagulation: a systematic review and meta-analysis. The Lancet 2006;367:404-11. |
|||
|
|
|||
|
Joergen Jespersen, EAA Chairman European Action on Anticoagulation (EAA), Leon Poller, Michelle Keown, Saied A Ibrahim, Felix JM van der Meer, Anton MHP van den Besselaar, Armando Tripodi, Joergen Jespersen, Pieter Meijer and Cornelis Kluft
Send letter to journal:
ecaa{at}manchester.ac.uk Joergen Jespersen, et al.
|
Response to letter from Siegmund L. Braun, for the German Association of Self Management of Anticoagulation (ASA e.V.) (7 November 2006), regarding Quality Assessment of CoaguChek Point-of-Care Prothrombin Time Monitors: Comparison of the European Community-Approved Procedure and Conventional External Quality Assessment (Clin Chem 2006;52:1843-1847) The following are our replies to Dr Braun's main points: (1) "Lyophilized plasma sample is not the intended use sample for this system". The reliability of the substitution of plasma for whole blood measurements on the CoaguChek using the formulation of calcium chloride and citrated plasma developed by the European Concerted Action on Anticoagulation has been demonstrated in a series of published reports (see references 1-5). (2) "An alternative quality assessment using the split-sample procedure is much more appropriate". The main criticism of the split-sample method which he recommends is that it only deals with the stochastic variation, agreement or imprecision and not with deviation from the true value, bias or inaccuracy. The ECAA introduced an external quality assessment procedure taking into account both imprecision and inaccuracy capable of being applied to the WHO prothrombin time system as international normalised ratios (INR). (3) "The reliability of INR results obtained with the CoaguChek system using whole blood has been proven in the recently published meta- analysis by Heneghan (his reference no 7)". The Lancet meta-analysis was we agree encouraging clinically but this in no way replaces a reliable system of external quality assessment of individual CoaguChek monitors and their users. The clinical benefit shown in the Lancet report is not proof of the reliability of the INR on the individual CoaguChek monitor. Other influences in the select group of patients capable of self-testing and self-dosage using CoaguChek monitors may have played part in the reported clinical benefit. References 1. L Poller, M Keown, N Chauhan, AMHP van den Besselaar, A Tripodi, C Shiach, J Jespersen. Comparison of fresh plasma and whole blood multicentre ISI calibrations of CoaguChek Mini and TAS PT-NC whole blood prothrombin time point-of-care monitors. Thromb Haemost 2002a;87:859-66. 2. L Poller, M Keown, N Chauhan, AMHP van den Besselaar, A Tripodi, J Jespersen, C Shiach. Minimum numbers of fresh whole blood and plasma samples from patients and healthy subjects for ISI calibration of CoaguChek and RapidPointCoag monitors. Am J Clin Pathol 2002b;117:892-9. 3. L Poller, M Keown, N Chauhan, AMHP van den Besselaar, A Tripodi, C Shiach, J Jespersen. 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. Clin Chem 2002c;48:1672-80. 4. L Poller, M Keown, N Chauhan, AMHP van den Besselaar, A Tripodi, C Shiach, J Jespersen . An assessment of lyophilised plasmas for ISI calibration of CoaguChek and TAS whole blood prothrombin time monitors. J Clin Pathol 2003a;56:114-119. 5. L Poller, M Keown, N Chauhan, AMHP van den Besselaar, A Tripodi, C Shiach, J Jespersen. An assessment of a method for ISI calibration of two whole blood point-of-care PT monitor systems based on lyophilised plasmas using whole blood equivalent PT. J Thromb Haemost 2003b;1:766-772. |
|||
|
|
|||
|
Michael Spannagl, Ph.D, M.D. INSTAND e.V., P.O. Box 250211 D-40093 Düsseldorf, Germany, Andrea Dick, Hans Reinauer
Send letter to journal:
mispannagl{at}t-online.de Michael Spannagl, et al.
|
The aim of the study performed by Poller et al was to validate the use of lyophilized plasma samples with assigned INR values for external quality assessment (EQA) of CoaguChek point of care testing prothrombin time monitor (Roche). The quality assessment concept uses a selected set of 5 lyophilized QA plasmas with assigned CoaguChek INR values determining deviations of individual QA plasmas from certified INR. In contrast to this method conventional QA schemes are based on calculation of the mean or median INR values and the standard deviation of all measurement results submitted by the participants involved in an exercise. The authors conclude that “with both analyses the overall performance of the CoaguChek monitor in the hand of experienced users is reasonably satisfactory, although individual monitors are shown to require QA.” Furthermore the “study shows that a proportion of CoaguChek monitors in current everyday use for dosage control give unsatisfactory results by both methods of analysis, a problem that needs to be addressed. “ First it is important to emphasize that all results and statements of Poller et al are based on the use of lyophilized plasma samples on the CoaguChek self measurement system which in contrast is calibrated for use with whole blood. It is well known, also for other analytes, that results gained from lyophilized plasma samples not always reflect the performance of a test system in the native sample, actually whole blood. INSTAND, the German Centre for Quality assurance and standardization in Laboratory Medicine does not offer an EQA program for patients performing self measurement of INR values. More than 110000 patients using these machines in Germany make a general proficiency testing impossible. Coagulation clinics and teaching family doctors may participate in these surveys. Target values and acceptability ranges of plasma samples expected to be obtained by EQAS* participant laboratories are not defined in advance by reference laboratories in each survey from EQAS. In fact they are based on calculation of the mean value and the standard deviation of all submitted and checked measurement results. According to our experience with patient self management of oral anticoagulation in Germany we decided against EQA from the perspective of a central EQA organizer in Germany but for a total quality management process for these pocket machines. Several elements in a total quality management process contribute to a reliable outcome in patients using self management of oral anticoagulants. First prerequisite is a system calibration and traceability according to the WHO model of PT calibration. An intense system, reagent and instrument verification as well as user validation studies by the patients contribute to reliable patient results. In a third step, careful selection of health care professionals and the selection of suitable patients for self-testing and the use of certified distinctive patient education procedures are mandatory1. Recent publications and meta-analysis2,3 dealing with the routine application under field conditions confirm the good outcome data presented in the earlier manufacturer sponsored studies. * external quality assessment schemes 1. Ansell J, Jacobson A, Levy J, Völler H, Hasenkam JM. Guidelines for implementation of patient self-testing and patient self-management of oral anticoagulation. International consensus guidelines prepared by International Self-Monitoring Association for Oral Anticoagulation. Int J Cardiol 2005; 99:37-45 2. Menendez- Jandula B, Souto JC, Oliver A, Montserrat I, et al. Comparing self-management of oral anticoagulant therapy with clinic management. Ann Intern Med 2005; 142:1-10 3. Heneghan C, Alonso-Coello P, Garcia-Alamino JM, Perera R, Meats E, Glasziou P. Self-monitoring of oral anticoagulation: a systematic review and meta-analysis. Lancet 2006; 367: 404-411. |
|||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH |