Impact of Viral Load Monitoring on Retention and Viral Suppression: A Regression Discontinuity Analysis of South Africa’s National Laboratory Cohort

South African guidelines recommend repeat viral load testing within 6 months when human immunodeficiency virus (HIV) viral loads exceed 1,000 copies/mL. We assessed whether South African facilities follow viral load monitoring guidelines and whether guidelines improve HIV-related outcomes, using a regression discontinuity design in a national HIV cohort of 174,574 patients (2013–2015). We assessed whether patients with viral loads just above versus just below 1,000 copies/mL were more likely to receive repeat testing in 6 months, and we compared differences in clinic transfers, retention, and viral suppression. The majority (67%) of patients with viral loads of >1,000 copies/mL did not receive repeat testing within 6 months, and these patients were 8.0% (95% confidence interval (CI): 6.2, 9.7) more likely to receive repeat testing compared with ≤1,000 copies/mL. Eligibility for repeat testing (>1,000 copies/mL) was associated with greater 12-month retention (risk difference = 2.9%, 95% CI: 0.6, 5.2) and combined suppression and retention (risk difference = 5.8%, 95% CI: 3.0, 8.6). Patients with viral loads of >1,000 copies/mL who actually received repeat testing were 85.2% more likely to be both retained and virally suppressed at 12 months (95% CI: 35.9, 100.0). Viral load monitoring might improve patient outcomes, but most patients with elevated viral loads do not receive monitoring within recommended timelines.