Single-Step Microfluidic Anti-Factor Xa Assay: Development and Clinical Evaluation in Patients on Low-Molecular-Weight Heparin

Direct oral anticoagulants and low-molecular-weight heparins (LMWHs) act principally through inhibition of activated factor X (FXa), yet no point-of-care assay for anti-FXa activity is in routine clinical use. This study reports a disposable microfluidic device that performs a single-step colorimetric anti-FXa assay on plasma. The chip was fabricated by laminating laser-cut poly(methyl methacrylate) sheets with adhesive tape; both assay reagents were pre-stored on-chip in dried form, and absorbance was measured at 405 nm. In 58 plasma samples from patients receiving LMWH therapy, the on-chip result correlated moderately with the automated laboratory assay. Benchmarking against the same reagents in a microwell plate showed that the device recovered 46% of the attainable agreement. The microfluidic assay identified samples at or above a therapeutic anti-Xa concentration with 94% specificity and a positive predictive value of 96%. The device is therefore suited to rapid screening prior to laboratory confirmation.