Background/Purpose: Over 33% of U.S. adults have limited health literacy or numeracy. Limited health literacy and numeracy have been associated with higher disease activity and worse patient-reported outcomes in systemic lupus erythematosus (SLE). Health literacy involves ability to understand and use health information. A component of health literacy is numeracy, which involves quantitative math skills and is important for understanding and managing complex medication regimens. The objective of this study was to assess the relationship between health numeracy and medication adherence in SLE; we hypothesized that patients with limited numeracy would have higher rates of medication non-adherence.

Methods: SLE patients meeting ACR or SLICC criteria were recruited from a university clinic from March 2019 through January 2021. Numeracy was assessed with the Subjective Numeracy Scale (SNS-3); limited numeracy was defined as SNS-3 ≤ 12. Self-reported adherence for SLE medications was obtained using the visual analog scale component of the MASRI (Medication Adherence Self-Report Inventory), a patient-reported percentage of taking medications in the past 1 month (0-100%). In a subset of patients (n=146), objective medication adherence to SLE medications was also determined by Medication Possession Ratio (MPR), the proportion of days with medication supply over a 3-month period, using pharmacy refill data from the electronic health record. Non-adherence was defined as MASRI < 90% and MPR < 80%. We evaluated relationships between numeracy and adherence using descriptive statistics. Logistic regression models estimated the associations of numeracy with non-adherence, adjusting for education level.

Results: The cohort included 218 patients with SLE. The average age was 43, with 94% female and 59% Black race. Mean disease duration was 13 years, with average SLEDAI 3.0 and PGA 0.5; 45% had a history of lupus nephritis.

Compared to patients with adequate numeracy, those with limited numeracy had lower self-reported adherence (54% vs 73%) but paradoxically higher objective adherence (56% vs 44%). In a multivariable logistic regression adjusted for education, patients with low numeracy were twice as likely to self-report non-adherence by MASRI (OR 1.94; 95% CI: 1.07, 3.51) (Table 1).

Conclusion: In our cohort, limited numeracy and non-adherence are common. Although patients with low numeracy filled SLE medications at similar rates to those with adequate numeracy, we found paradoxically they were more likely to report non-adherence. This may reflect true non-adherence but could also be due to difficulty interpreting the adherence question or estimating the percentage they have taken medications. Future studies are needed to further elucidate this relationship.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/association-of-numeracy-with-medication-non-adherence-in-systemic-lupus-erythematosus/