A Comparison of Calibration Curves Using Unfractionated Heparin, Enoxaparin, Dalteparin, and Fondaparinux in a Chromogenic Anti-FXa Assay

Abstract number: P0711

Bethel M, Adcock DM, Ramanathan R

When monitoring anti-Xa therapeutic agents with a chromogenic anti-FXa assay, a calibration curve is typically prepared using the particular drug to be measured. In this study, we compared the calibration curves obtained with each of 4 different commonly used anticoagulant drugs. Calibration curves were compared to determine if the variability warranted use of a curve specific to each drug, or if a single curve could be used and accurate results for any of the drugs still obtained.

Methods:  The anti-FXa assay used for this study was the Stachrom^® Heparin assay from Diagnostica Stago (Asnières, France), performed on a STA-R analyzer. Each of the 4 drugs was spiked into pooled normal plasma from Precision Biologic (Dartmouth, NS, Canada) at various concentrations to produce the calibration curves. High, mid-level, and low reaction rates were calculated from each calibration curve, and the resulting concentration compared for accuracy and clinical significance.

Data:

Conclusion:  The calibration curves for enoxaparin and dalteparin were similar enough that either can serve as the calibrator when measuring these low molecular weight heparins. The data show that samples containing unfractionated heparin or fondaparinux should be evaluated using a drug-specific calibrator, especially as they are measured in different units.