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Background. Biological variation is usually estimated in healthy individuals during steady-state conditions. The aim of this study was to estimate the in-treatment biological variation of the International normalised ratio (INR) and to investigate to what extent the different levels of coagulation factors could explain this variation. Methods. Blood samples were collected from randomly included patients 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 ™ ). The level of fiand the activity of coagulation factors II, V, VII and X were determined. Results. The in-treatment within- and between-subject coeffi cients of variation of INR were dependent on the method and varied between 18 and 24% and 13 and 19%, respectively, and were reduced to 3.9 – 5.1% and 2.3 – 5.8%, after correction for coagulation factors which could explain 91 – 95% of the variance of INR. Conclusions. The in-treatment biological variation of INR was higher than reported for healthy individuals as well as patients in a steady-state condition, but by correcting for appropriate coagulation factors it was reduced. The association between INR and coagulation factors was different for the different PT methods mainly due to different sensitivity towards FII and FVII.

To the Editor: Accurate and reproducible blood glucose results are important for adequate therapeutic decision for people with diabetes. Few studies assessing the accuracy of systems for self-monitoring of blood glucose (SMBG)1 systems against the requirements from the International Organization for Standardization (ISO) standard 15197:2013 (1) have been published, and none of them has addressed analytical quality in the hands of the users. To our knowledge, no studies have evaluated SMBG systems against the requirements for accuracy in the new US Food and Drug Administration (FDA) draft guidance for SMBG systems for over-the-counter use (2). The aim of this study was to assess the accuracy of 10 SMBG systems under optimal conditions achieved by biomedical laboratory scientists (BLSs) and by people with diabetes against the minimum accuracy requirements specified in ISO 15197:2013, ISO 15197:2003, and FDA draft guidance. We used data from 10 SMBG system evaluations performed from 2005 to 2013 by the Scandinavian evaluation of laboratory equipment for primary healthcare (SKUP). The evaluations were carried out in line with common guidelines and standardized protocols according to international recommendations. All measurements on …

Regular measurement of prothrombin time as an international normalized ratio PT (INR) is mandatory for optimal and safe use of warfarin. Scandinavian evaluation of laboratory equipment for primary health care (SKUP) evaluated the microINR portable coagulometer (microINR(®)) (iLine Microsystems S.L., Spain) for measurement of PT (INR). Analytical quality and user-friendliness were evaluated under optimal conditions at an accredited hospital laboratory and at two primary health care centres (PHCCs). Patients were recruited at the outpatient clinic of the Laboratory of Medical Biochemistry, St Olav's University Hospital, Trondheim, Norway (n = 98) and from two PHCCs (n = 88). Venous blood samples were analyzed under optimal conditions on the STA-R(®)Evolution with STA-SPA + reagent (Stago, France) (Owren method), and the results were compared to capillary measurements on the microINR(®). The imprecision of the microINR(®) was 6% (90% CI: 5.3-7.0%) and 6.3% (90% CI: 5.1-8.3) in the outpatient clinic and PHCC2, respectively for INR ≥2.5. The microINR(®) did not meet the SKUP quality requirement for imprecision ≤5.0%. For INR

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.

BACKGROUND Observed differences between results obtained from comparison of instruments used to measure international normalized ratio (INR) have been higher than expected from the imprecision of the instruments. In this study the variation of these differences was divided into subcomponents, and each of the subcomponents was estimated. METHODS Blood samples were collected at 4 different patient visits from each of 36 outpatients who were receiving warfarin treatment and were included in the study. INR was determined on 1 laboratory instrument (STA Compact®) and 3 point-of-care instruments (Simple Simon®PT, CoaguChek®XS, and INRatio™). All 4 INR instruments were compared in pairs. Linear regression was used to correct for systematic deviations. The remaining variation of the differences was subdivided into between-subject, within-subject, and analytical variation in an ANOVA nested design. RESULTS The mean difference between instruments varied between 1.0% and 14.3%. Between-subject variation of the differences (expressed as CV) varied between 3.3% and 7.4%, whereas within-subject variation of the differences was approximately 5% for all 6 comparisons. The analytical imprecision of the differences varied between 3.8% and 8.6%. CONCLUSIONS The differences in INR between instruments were subdivided into calibration differences, between- and within-subject variation, and analytical imprecision. The magnitude of each subcomponent was estimated. Within results for individual patients the difference in INR between 2 instruments varied over time. The reasons for the between- and within-subject variations of the differences can probably be ascribed to different patient-specific effects in the patient plasma. To minimize this variation in a monitoring situation, each site and patient should use results from only 1 type of instrument.

Instruments for self-monitoring of blood glucose (SMBG) should undergo a standardized evaluation including a user-test before being marketed. In this study the results from standardized evaluations of nine different SMBG instruments are presented, and the standardized evaluation is discussed.Approximately 80 diabetes patients using three lots of test strips participated in each evaluation. Half of the patients were educated in how to use the meter, and the evaluations were carried out by both medical laboratory technologists (MLTs) and patients. Questionnaires were used to assess the user manual and the user-friendliness of the instrument.The imprecision obtained by the patients (coefficients of variation [CVs] of 3.2-8.1%) were generally higher compared to that by the MLT (CVs of 2.3-5.9%). Three of the nine instruments did not achieve the quality goal based on the recommendation in the International Organization for Standardization's ISO 15197 guideline in the hands of diabetes patients. The bias from the comparison method ranged from -10.4% to +3.2%. There were significant lot-to-lot variations and hematocrit effects for some of the instruments. Temperature difference between the instruments and the test strip caused deterioration of the quality in one instrument. The user-friendliness was in general acceptable.The quality of instruments for SMBG seems to have improved during recent years, although there are still analytical problems. A standardized evaluation protocol is necessary and should be regularly revised taking into account the development of new technology and the needs of the patients.