Cross-sectional and longitudinal performance of creatinine- and cystatin C-based estimating equations relative to exogenously measured glomerular filtration rate in HIV-positive and HIV-negative persons.

BACKGROUND Reliable estimates of glomerular filtration rate (GFR) are important in the clinical management of HIV-positive patients. Data on the performance of widely used estimating equations (eGFR) relative to exogenously measured GFR are sparse in this population. METHODS We evaluated cross-sectional and longitudinal accuracy and bias of eGFR, based on creatinine and cystatin C, relative to disappearance of infused iohexol from plasma (iGFR) in a cohort of participants followed annually for up to 7 years. RESULTS 222 HIV-positive and 139 HIV-negative participants contributed 1,240 visits with valid iGFR and eGFR measures. Estimated GFR based on both creatinine and cystatin C performed the best. Estimated GFR based on creatinine alone overestimated iGFR by 9 mL/min/1.73m2 on average and was significantly less accurate in HIV-positive than HIV-negative individuals. The performance of equations based on either creatinine alone or cystatin C alone were significantly affected by participant factors (e.g., non-suppressed HIV RNA, nadir CD4 count, hepatitis C virus coinfection). The average iGFR slope was -4% per year in HIV-positive participants. In both HIV-positive and HIV-negative participants, eGFR slope measures were generally unbiased but inaccurate, with only 60% to 74% of observations falling within ± 5 percentage points of iGFR slope. CONCLUSION Both creatinine and cystatin C have limitations as GFR indices in HIV-positive individuals. Estimated GFR based on both creatinine and cystatin C performed best in our study and may be preferred in HIV-positive persons with kidney disease or comorbidities that place them at high risk for kidney disease.