Key result
The predicted chromogenic factor X from INRs over the range of 1.4-2.2 was 7-18% higher in patients initiating warfarin compared with those on chronic warfarin therapy.
Why the study?
Does the relationship between chromogenic factor X and INR differ during early warfarin initiation compared with chronic warfarin administration?
Observational (n=301)
No
Does the relationship between chromogenic factor X and INR differ during early warfarin initiation compared with chronic warfarin administration?
The relationship between CFX and INR differs significantly between warfarin initiation and chronic maintenance, requiring situation-specific equations for accurate translation in clinical protocols.
May require distinct CFX interpretation for warfarin initiators versus chronic users; hypothesis-generating and requires outcome studies before adoption.
Chromogenic factor X (CFX) monitoring is necessary in patients with potential international normalized ratio (INR) artifacts during warfarin therapy. The relationship of CFX with the INR needs to be quantitated to have warfarin protocols that are equivalent with either test as a monitoring parameter. This study investigated whether the CFX/INR relationship is different during warfarin initiation compared with that during chronic warfarin therapy. Outpatients (N = 164) taking chronic doses of warfarin and inpatients (N = 137) initiating warfarin therapy had plasma samples tested for CFX and INR. The best fit mathematical relationship of CFX and INR was determined for both groups. A six hundred and twenty-five bed, adult-only, private, tertiary care teaching hospital was the setting of the study. The best fit equation for chronic warfarin patients was quadratic using a reciprocal transformation of the INR. The best fit equation for the warfarin initiation patients was linear using logarithmic transformation of CFX and INR. The predicted CFX from INRs over the range of 1.4-2.2 was 7-18% higher in the warfarin initiation patients than in the chronic warfarin patients. Translation of CFX values into equivalent INRs for use in warfarin initiation and maintenance protocols is improved when using equations specific to the patient situation.
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Rosborough et al. (2009) conducted an observational in Warfarin therapy (n=301). Warfarin initiation vs. Chronic warfarin administration was evaluated on Relationship between chromogenic factor X and INR. The predicted chromogenic factor X from INRs over the range of 1.4-2.2 was 7-18% higher in patients initiating warfarin compared with those on chronic warfarin therapy.
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