Differences between self-reported and electronically monitored adherence among patients receiving antiretroviral therapy in a resource-limited setting

Background: Measurement of adherence to antiretroviral therapy (ART) by patient self-report is common in resource-limited settings but widely believed to overstate actual adherence. The extent to which these measures overstate adherence has not been examined among a large patient population. Methods: HIV-infected adult patients in Kenya who initiated ART within the past 3 months were followed for 6 months. Adherence was measured by participants' self-reports of doses missed in the past 7 days during monthly clinic visits and by continuous Medication Event Monitoring System (MEMS) in participants' pill bottles. Seven-day self-reported adherence was compared to 7-day MEMS adherence, 30-day MEMS adherence, and adherence more than 90% during each of the first 6 months. Results: Self-reported and MEMS adherence measures were linked for 669 participants. Mean 7-day self-reported adherence was 98.7% and mean 7-day MEMS adherence was 86.0%, a difference of 12.7% (P < 0.01). The difference between the two adherence measures increased over time due to a decline in 7-day MEMS adherence. However, patients with lower MEMS adherence were in fact more likely to self-report missed doses and the difference between self-reported and MEMS adherence was similar for each number of self-reported missed doses. When analysis was limited to patients who reported rarely or never removing multiple doses at the same time, mean difference was 10.5% (P < 0.01). Conclusion: There is a sizable and significant difference between self-reported and MEMS adherence. However, a strong relationship between the measures suggests that self-reported adherence is informative for clinical monitoring and program evaluation.