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Activated protein C resistance assay performance: improvement by sample dilution with factor V-deficient plasma
F J Strobl1, S Hoffman, S Huber
1Department of Pathology, University of Wisconsin Medical School, Madison, USA.
Objective:
To evaluate a modification of a commercially available reagent kit (COATEST APC Resistance Kit) for functional activated protein C (APC) resistance testing, and to determine the ability of the modified assay to demonstrate APC resistance in patients receiving warfarin.
Design:
Functional APC resistance testing was performed using both the first-generation COATEST APC Resistance Kit and a modified, or second-generation, version of the COATEST assay that uses predilution of the patient sample with factor V-deficient plasma. Factor V genotyping for APC resistance (FV R506Q) was performed using a well-characterized polymerase chain reaction-restriction fragment length polymorphism method.
Setting:
University medical center.
Patients:
Seventy-three individuals referred for hypercoagulability testing who were not receiving warfarin therapy and 29 patients with a history of venous thrombosis who were receiving warfarin therapy.
Main Outcome Measure:
Sensitivity and specificity as determined by comparing functional APC resistance to the FV R506Q genotype.
Results:
In 73 patients referred for hypercoagulability testing, but not receiving warfarin therapy, a sensitivity of 0.86 and a specificity of 0.75 were obtained with the first-generation COATEST assay. In contrast, a sensitivity and specificity of 1.0 were obtained when the second-generation COATEST assay was employed. In 29 patients receiving warfarin, the first-generation assay exhibited a sensitivity and specificity of 0.88 and 0.95, respectively, whereas the sensitivity and specificity for the second-generation assay was 1.0.
Conclusions:
Predilution of patient plasma with factor V-deficient plasma results in improved sensitivity and specificity of the COATEST APC Resistance Kit, thus offering a simple modification to enhance APC resistance determination in the routine clinical laboratory setting.