Use of the chromogenic factor X assay to predict the international normalized ratio in patients transitioning from argatroban to warfarin.
OBJECTIVE
To determine the clinical utility of the chromogenic factor X level for conversion from argatroban to warfarin in hospitalized patients.


METHODS
Prospective observational study.


METHODS
Sixty-two hospitalized patients with indications for anticoagulation in whom the chromogenic factor X assay was used for conversion from argatroban to warfarin.


METHODS
University-affiliated hospital.


METHODS
From December 2003-May 2004, data for all patients in whom the chromogenic factor X assay was used for conversion from argatroban to warfarin were screened for inclusion. When the chromogenic factor X level was satisfactory, the clinician discontinued the argatroban and a confirmatory international normalized ratio (INR) was obtained.


RESULTS
To determine the ability of the chromogenic factor X level to predict the INR free of argatroban influence, we calculated the sensitivity and specificity by using a cutoff chromogenic factor X level of 45% or less, or greater than 45%, which corresponded to an INR of 2 or greater, or less than 2, respectively. We constructed a receiver operating characteristic curve to illustrate various cutoff levels of chromogenic factor X. Of 146 patients screened, 62 had data that met criteria for analysis. An average of 6 +/- 3 doses of warfarin were administered before the confirmatory coagulation studies were obtained. The average time from the chromogenic factor X measurement to obtainment of confirmatory coagulation studies was 9 +/- 4 hours. Use of a chromogenic factor X level of 45% or less to predict an INR of 2 or greater absent of argatroban influence had a sensitivity of 93%, a specificity of 78%, and an accuracy of 89%. The area under the receiver operating characteristic curve was 0.91 (95% confidence interval 0.81-0.99, p<0.0001).


CONCLUSIONS
The chromogenic factor X level is an accurate alternative when converting hospitalized patients from argatroban to warfarin. A chromogenic factor X level of 45% or less is a reliable predictor that the INR will be therapeutic when argatroban therapy is discontinued.
Arpino
Paul A
PA
Department of Pharmacy, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114, USA. parpino@partners.org
Demirjian
Zareh
Z
Van Cott
Elizabeth M
EM
D000368:Aged; D000925:Anticoagulants / Q000494:pharmacology* / Q000627:therapeutic use; D001120:Arginine / Q000031:analogs & derivatives; D001777:Blood Coagulation / Q000187:drug effects; D002863:Chromogenic Compounds; D005170:Factor X / Q000187:drug effects*; D005260:Female; D006785:Hospitals, University; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D008875:Middle Aged; D010875:Pipecolic Acids / Q000494:pharmacology* / Q000627:therapeutic use; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012372:ROC Curve; D013449:Sulfonamides; D014859:Warfarin / Q000494:pharmacology* / Q000627:therapeutic use
D000925:Anticoagulants; D002863:Chromogenic Compounds; D010875:Pipecolic Acids; D013449:Sulfonamides; D014859:Warfarin; D005170:Factor X; D001120:Arginine; C031942:argatroban