Falsely elevated international normalized ratio values in patients undergoing anticoagulation therapy: a descriptive evaluation.
BACKGROUND
Elevated international normalized ratio (INR) values have been linked to bleeding complications; however, elevated INR values are not always physiologic and can be falsely increased. This study describes the rate of falsely elevated INRs and characteristics predictive of falsely elevated INRs.


METHODS
This cross-sectional study was conducted among adult patients receiving anticoagulation therapy monitored by a centralized anticoagulation service during January 2000 through December 2004 (n = 29,536). Prevalence rates of all elevated (ie, value >/= 10), falsely elevated, and truly elevated INRs were calculated. Multivariate logistic regression was performed to identify predictors of falsely elevated INRs among elevated INRs.


RESULTS
Of the 556,998 INRs included in the analysis, 793 INRs (prevalence, 0.14%; 95% confidence interval [CI], 0.10 to 0.19%), 53 INRs (prevalence, 0.01%; 95% CI, < 0.01 to 0.03%), and 740 INRs (prevalence, 0.13%; 95% CI, 0.09 to 0.18%) were elevated, falsely elevated, and truly elevated, respectively. The strongest independent predictor of a falsely elevated INR was a patient undergoing hemodialysis at the time of the elevated INR (adjusted odds ratio, 9.60; 95% CI, 4.96 to 18.58; p < 0.001). A low target INR was the only other factor found to be an independent predictor of a falsely elevated INR.


CONCLUSIONS
Although INR values >/= 10.0 occur infrequently, patients presenting with such values can present a challenge to the anticoagulation provider. Anticoagulation providers should be particularly vigilant for falsely elevated INRs when monitoring patients undergoing hemodialysis.
Delate
Thomas
T
Clinical Pharmacy Research Team, Kaiser Permanente Colorado, Aurora, CO.
Witt
Daniel M
DM
Clinical Pharmacy Anticoagulation Services, Kaiser Permanente Colorado, Aurora, CO. Electronic address: dan.m.witt@kp.org.
Jones
Jared R
JR
Clinical Pharmacy Anticoagulation Services, Kaiser Permanente Colorado, Aurora, CO.
Bhardwaja
Bharati
B
Clinical Pharmacy Services-Nephrology, Kaiser Permanente Colorado, Aurora, CO.
Senser
Martin
M
Clinical Pharmacy Anticoagulation Services, Kaiser Permanente Colorado, Aurora, CO.
D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000008:administration & dosage* / Q000009:adverse effects; D003430:Cross-Sectional Studies; D005189:False Positive Reactions; D005260:Female; D006470:Hemorrhage / Q000097:blood / Q000139:chemically induced; D006801:Humans; D019934:International Normalized Ratio / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D016017:Odds Ratio; D006435:Renal Dialysis; D012307:Risk Factors; D014859:Warfarin / Q000008:administration & dosage* / Q000009:adverse effects
D000925:Anticoagulants; D014859:Warfarin