HIV Viremia and T-Cell Activation Differentially Affect the Performance of Glomerular Filtration Rate Equations Based on Creatinine and Cystatin C

BACKGROUND: Serum creatinine and cystatin C are used as markers of glomerular filtration rate (GFR). The performance of these GFR markers relative to exogenously measured GFR (mGFR) in HIV-positive individuals is not well established. METHODS: We assessed the performance of the chronic kidney disease epidemiology collaboration equations based on serum concentrations of creatinine (eGFR(cr)), cystatin C (eGFR(cys)) and both biomarkers combined (eGFR(cr-cys)) in 187 HIV-positive and 98 HIV-negative participants. Measured GFR was calculated by plasma iohexol clearance. Bias and accuracy were defined as the difference between eGFR and mGFR and the percentage of eGFR observations within 30% of mGFR, respectively. Activated CD4 and CD8 T-cells (CD38+ HLA-DR+) were measured by flow cytometry. RESULTS: The median mGFR was >100 ml/min/1.73 m(2) in both groups. All equations tended to be less accurate in HIV-positive than in HIV-negative subjects, with eGFR(cr-cys) being the most accurate overall. In the HIV-positive group, eGFR(cys) was significantly less accurate and more biased than eGFR(cr) and eGFR(cr_cys). Additionally eGFR(cys) bias and accuracy were strongly associated with use of antiretroviral therapy, HIV RNA suppression, and percentages of activated CD4 or CD8 T-cells. Hepatitis C seropositivity was associated with larger eGFR(cys) bias in both HIV-positive and HIV-negative groups. In contrast, eGFR(cr) accuracy and bias were not associated with HIV-related factors, T-cell activation, or hepatitis C. CONCLUSIONS: The performance of eGFR(cys) relative to mGFR was strongly correlated with HIV treatment factors and markers of T-cell activation, which may limit its usefulness as a GFR marker in this population.