Search

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.

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.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.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.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.