Validation of the ToDay, a simplified diagnostic algorithm for deep vein thrombosis

BACKGROUND: The current deep vein thrombosis (DVT) diagnostic algorithms are rarely followed in clinical practice due to complexity and time constraints. Simplified alternatives are needed to enhance adherence while maintaining diagnostic accuracy. The ToDay algorithm was developed to address these concerns by combining physician implicit assessment of DVT likelihood with D-dimer testing. OBJECTIVES: The objective of the study is to validate the ToDay algorithm using previously collected data. METHODS: This analysis used data from the 4D study (NCT02038530), a multicenter study evaluating DVT diagnostic strategies. The ToDay algorithm considers DVT excluded without further testing if DVT is considered most likely and D-dimer <500 ng/mL or if DVT is not considered most likely and D-dimer less than age-adjusted threshold. The primary outcome was 90-day symptomatic venous thromboembolism (VTE). Secondary outcome was not requiring ultrasound imaging. RESULTS: Among 1497 patients, 163 (10.9%) were diagnosed with DVT. Of the 1334 patients who had DVT excluded by the ToDay algorithm, 10 patients were found to have VTE during follow-up, a failure rate of 0.75% (95% CI, 0.41-1.37). Of all patients, 38.6% (95% CI, 36.2-41.1) did not require ultrasound imaging. CONCLUSION: The ToDay algorithm was found to be a safe and efficient alternative for DVT testing, reducing reliance on ultrasound imaging. It simplifies the diagnostic process, making it more feasible for emergency settings. Prospective validation is required before clinical adoption.