Diagnostic Performance of a DOAC Urine Dipstick in Obese Outpatients with Atrial Fibrillation: Comparison with Plasma Concentrations.

Background

atrial fibrillation (AF) patients with obesity and high thromboembolic risk need oral anticoagulant therapy. Limited data are available on direct oral anticoagulants (DOACs) in this population, and a point-of-care method has been validated to support rapid clinical decisions and to identify on-off plasma concentration thresholds.

Methods

This is a monocentric, cross-sectional diagnostic accuracy study on obese AF outpatients referred to Policlinico Umberto I of Rome. Urinary Dipsticks were assessed with separate pads for factor Xa (FXA-i) and thrombin inhibitor (THR-i) and compared to the reference standard of trough and peak plasma concentrations with chromogenic assays/dTT and prespecified plasma thresholds for each DOAC. Study endpoints were the sensitivity, specificity, positive and negative predictive values (PPV and NPV) of DOACs Dipstick compared to plasma concentrations. Sub-analyses according to obesity severity and type of DOAC were performed.

Results

320 paired plasma and urine samples were available from 160 enrolled patients (mean age 73.2 ± 9.1 years). Compared to trough plasma concentrations, DOACs Dipstick showed a sensitivity of 99.24% (mean, 95% confidence interval, CI 95.82-99.98), specificity of 6.89% (0.85-22.76), PPV 82.80% (81.32-84.18), NPV 66.67% (15.79-95.52). On the other hand, compared to peak plasma concentrations, DOACs Dipstick showed a sensitivity of 97.8% (93.7-99.5), specificity of 0% (0.0-15.4), and PPV of 85.9% (85.6-86.2). Urinary Dipstick showed a sensitivity of 99.10% (95.4-100.0), specificity of 4.70% (0.60-16.20) and a PPV and NPV of 74.50% (73.2-75.8) and 66.70 (15.7-95.6), compared to plasma thresholds > 30 ng/mL of FXA-I and THR-I. Sub-analyses showed similar results between FXA-i and THR-i.

Conclusions

The urine point-of-care has high sensitivity, acceptable PPV, but low specificity and NPV in AF obese patients and may be useful only in selected clinical scenarios.