Health disparities in patient-reported outcomes by income and education are well documented; however, the impact of health literacy on patient-reported outcomes has received less attention. We examined independent effects of income, education, and health literacy on patient-reported outcomes in systemic lupus erythematosus (SLE).
Data from the California Lupus Epidemiology Study (n = 323 participants) were used. Health literacy was assessed with a validated 3-item measure (ability to understand written information, reliance on others to understand written information, confidence in completing written forms). Patient-reported outcomes were administered by interview in English, Spanish, Cantonese, or Mandarin. Generic and disease-specific patient-reported outcomes were examined using the following: 10 Patient-Reported Outcomes Measurement Information System (PROMIS) short forms; the 8 Short Form 36 (SF-36) health survey subscales; and 3 patient-reported SLE disease activity and damage measures. We conducted 2 sets of multivariable analyses: the first examined education, income, or health literacy individually; the second included all 3 simultaneously. All multivariable models included age, sex, race/ethnicity, language, disease duration, and physician-assessed disease activity and damage.
More than one-third of participants (38%) had limited health literacy (LHL), including >25% with greater than high school education. In multivariable analyses simultaneously considering education, income, and health literacy, LHL was associated with significantly worse scores on all patient-reported outcomes except disease damage. In contrast, disparities by income were seen in only 3 PROMIS scales, 3 SF-36 subscales, and 1 disease activity measure. No disparities by education level were noted.
We found significantly worse patient-reported outcome scores among individuals with LHL, even after controlling for disease activity and damage. Whether disparities are due to actual differences in health or measurement issues requires further study.