A Multi-instrument Evaluation of a Chromogenic Factor X Assay for Monitoring Oral Anticoagulation Therapy

Abstract number: P0112

Shaklee¹ P, McGlasson² D

¹¹Hemostasis Research Laboratory, BioCascade Incorporated, Arlington, WI, 53911, USA ²²59^th Clinical Research Squadron, Wilford Hall Medical Center, Lackland AFB, TX, 78236, USA

A multi-instrument evaluation of the chromogenic DiaPharma Factor X Assay kit (DFX) was undertaken to evaluate the utility of the kit for measuring factor X levels in patients receiving oral anticoagulation therapy (OAT) with unstable INRs. Two separate laboratories evaluated the DFX kit utilizing either microtiter (Lab 1) or STA Compact (Lab 2) instruments. Factor X levels were determined on 25 normal subject plasmas in both labs to establish a normal range. Additionally, each lab performed a clottable factor X (CFX) method on the same plasmas to determine normal ranges for statistical comparison. Both laboratories evaluated plasmas from 55 patients receiving OAT. The OAT plasmas were assayed for FX levels by DFX and CFX, and international normalized ratios (INR). Utilizing the DFX method, normal Factor X levels ranged from 72–147% with mean values of 113.8% and 120.4% in labs 1 and 2, respectively. Plasmas from patients on OAT, measured by DFX, showed a range of FX levels from 17–65%, with mean values of 31% and 32.5% in labs 1 and 2, respectively. Significant correlation (>0.9) of CFX and DFX methods was demonstrated in both labs. Patients on OAT with and without interfering substances, with the presence of a lupus anticoagulant (LA), and with unstable INR values were also evaluated with the DFX assay kit. Precision and accuracy testing using different levels of FX were analyzed by all methods at both institutions. Taken together, the present studies of the DFX kit demonstrated the assays robustness, precision, accuracy, and utility for monitoring patients on OAT with and without interfering substances, the presence of a LA or unstable INR. This assay should offer health care providers an option for monitoring patients receiving OAT, when INR values are not reliable due to the presence of a LA, and when bridging Argatroban® patients to warfarin.