Interruption of antiretroviral therapy is associated with increased plasma cystatin C

Background: Cystatin C has been proposed as an alternative marker of renal function. We sought to determine whether participants randomized to episodic use of antiretroviral therapy guided by CD4⁺ cell count (drug conservation) had altered cystatin C levels compared with those randomized to continuous antiretroviral therapy (viral suppression) in the Strategies for Management of Antiretroviral Therapy trial, and to identify factors associated with increased cystatin C. Methods: Cystatin C was measured in plasma collected at randomization, 1, 2, 4, 8 and 12 months after randomization in a random sample of 249 and 250 participants in the drug conservation and viral suppression groups, respectively. Logistic regression was used to model the odds of at least 0.15 mg/dl increase in cystatin C (1 SD) in the first month after randomization, adjusting for demographic and clinical characteristics. Results: At randomization, mean (SD) cystatin C level was 0.99 (0.26 mg/dl) and 1.01 (0.28 mg/dl) in the drug conservation and viral suppression arms, respectively (P = 0.29). In the first month after randomization, 21.8 and 10.6% had at least 0.15 mg/dl increase in cystatin C in the drug conservation and viral suppression arms, respectively (P = 0.0008). The difference in cystatin C between the treatment arms was maintained through 1 year after randomization. After adjustment, participants in the viral suppression arm had significantly reduced odds of at least 0.15 mg/dl increase in cystatin C in the first month (odds ratio 0.42; 95% confidence interval 0.23-0.74, P = 0.0023). Conclusion: These results demonstrate that interruption of antiretroviral therapy is associated with an increase in cystatin C, which may reflect worsened renal function.