The influence of coagulation factors on the in-treatment biological variation of international normalized ratio for patients on warfarin.
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 fibrinogen, and the activity of coagulation factors II, V, VII and X were determined.


RESULTS
The in-treatment within- and between-subject coefficients 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.
Department of Global Public Health and Primary Care, University of Bergen , Norway.
Una Ø
UØ
Sølvik
Thomas
T
Røraas
Per H
PH
Petersen
Anne
A
Stavelin
Grete
G
Monsen
Sverre
S
Sandberg
D000925:Anticoagulants / Q000627:therapeutic use*; D001779:Blood Coagulation Factors / Q000502:physiology*; D006801:Humans; D019934:International Normalized Ratio; D014859:Warfarin / Q000627:therapeutic use*
D000925:Anticoagulants; D001779:Blood Coagulation Factors; D014859:Warfarin
ANOVA; International normalised ratio (INR); blood coagulation factor; point-of-care system; warfarin