Cystatin C as a marker of renal function is affected by HIV replication leading to an underestimation of kidney function in HIV patients.

BACKGROUND: Broad use of tenofovir and an ageing HIV- infected population have created an interest in renal function in HIV patients. Serum cystatin C is a newer marker of renal function and might be more sensitive than creatinine. METHODS: Patients were enrolled consecutively in an observational study. HIV-seropositive patients naive to antiretroviral therapy (n = 261) were compared with healthy volunteers undergoing check-up procedures (n = 193). Estimated glomerular filtration rate (eGFR) was derived using creatinine-based Modification of Diet in Renal Disease (MDRD) and Cockcroft-Gault formulas or cystatin C-based calculations. HIV-seropositive patients starting antiretroviral therapy (n = 92) were followed prospectively after enrolment. RESULTS: MDRD showed a higher median eGFR in antiretroviral-naive HIV-seropositive patients compared with controls (104 versus 93 ml/min; P < 0.001). Cockcroft-Gault gave similar results (118 versus 106 ml/min; P < 0.001). By contrast, cystatin C levels in HIV-seropositive individuals were higher, resulting in a lower median eGFR compared with controls (99 versus 120 ml/min; P < 0.001). Cystatin C was positively correlated with HIV RNA (r = 0.33, P < 0.01) and inversely correlated with CD4+ T-cell count (r = -0.29, P < 0.01). Initiating antiretroviral therapy (n = 92) decreased cystatin C levels and led to an increased cystatin C-based eGFR from median 84 to 103 ml/min at week 24 (P < 0.001). Serum creatinine was not substantially altered. CONCLUSIONS: Correlation of cystatin C with HIV RNA and CD4+ T-cell count, plus decrease of cystatin C after suppression of HIV replication, suggest an increase of cystatin C levels by active HIV infection. This might result in overestimation of renal impairment, particularly in treatment-naive patients. Therefore, use of cystatin C to calculate GFR in HIV-seropositive individuals should not be recommended without further validation.