The Relationship Between Signature Time and Functional Health Literacy: Results from a Prospective Study of an Urban Low-Income Population Receiving Long-Term Anticoagulation

Introduction Low health literacy (HL) is consistently associated with worse health outcomes. Routine clinical screening with available instruments is impractical because of added time and effort. Prior findings suggested that signature time may be a reliable alternative measure of HL among general medicine patients. Methods Our aim was to assess the screening performance of signature time and explore optimal thresholds for identifying patients with limited HL in a chronically anticoagulated population. English-speaking patients receiving long-term anticoagulation therapy were recruited. HL was assessed using the Short Test of Functional Health Literacy in Adults (STOFHLA). Signature time was measured using a stopwatch. Logistic regression models and receiver-operating characteristic (ROC) curves were used to evaluate the association and accuracy of signature time compared to HL, respectively. Results Of 139 enrolled patients, mean age was 60.1 years, 70.5% were African-American, 48.9% reported < $25,000 income, and 27.3% had marginal or inadequate HL. Overall, median time to sign was 6.1 s. Signature time was longest with inadequate HL (median 9.5 s) compared to adequate HL (5.7 s; p < 0.01). Longer signature time was significantly associated with lower HL after adjusting for age and education (aOR 0.77, 95% CI: 0.68–0.88, p < 0.01). Signature time demonstrated high accuracy (area under the curve [AUC] > 0.8) in identifying HL levels. Thresholds of 5.1 s and 9.0 s showed appropriate screening performance in distinguishing patients with adequate vs. marginal and marginal vs. inadequate HL, respectively. Conclusion Signature time demonstrated strong screening performance and may offer a quick and practical approach to assessing HL among patients receiving long-term anticoagulation management.