Biological variation of INR in stable patients on long-term anticoagulation with warfarin.
Within-individual biological variation of INR (CV(B)) was assessed in 245 selected stable warfarin-treated patients monitored by three thrombosis centers. Selection criteria were: treatment period of six months or longer before the observation period; at least six consecutive INRs within the therapeutic range of 2.0 - 3.0; interval between consecutive INR measurements of two weeks or longer; no change in warfarin dose; no changes in the patient's circumstances which may influence the INR, such as intercurrent diseases, invasive procedures, starting or stopping drugs interacting with warfarin. The minimum, maximum and mean within-individual coefficient of variation CV(B) of the INR measurements in the 245 selected patients were 0.4%, 14.5%, and 9.0%, respectively Analytical performance goals for the INR measurement (imprecision) could be derived from the mean CV(B). For a therapeutic range of 2.0 - 3.0 with warfarin, the desirable and optimum imprecision of INR determination is <4.5% CV and <2.25% CV, respectively. The biological variation and analytical performance goals have been derived using classic laboratory methods but should be applicable to point-of-care testing as well.
Department of Thrombosis and Hemostasis, Leiden University Medical Center, Leiden, The Netherlands. a.m.h.p.van_den_besselaar@lumc.nl
Anton M H P
AM
van den Besselaar
Paola
P
Fogar
Vittorio
V
Pengo
Gualtiero
G
Palareti
Simon
S
Braham
Marco
M
Moia
Armando
A
Tripodi
D000368:Aged; D000925:Anticoagulants / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D019934:International Normalized Ratio / Q000706:statistics & numerical data*; D007558:Italy / Q000453:epidemiology; D008137:Longitudinal Studies; D008297:Male; D015995:Prevalence; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013927:Thrombosis / Q000097:blood* / Q000175:diagnosis / Q000517:prevention & control*; D014859:Warfarin / Q000008:administration & dosage*
D000925:Anticoagulants; D014859:Warfarin