Background: No study has determined the best equation for estimating renal function in patients with systemic lupus erythematosus (SLE), starting from a gold standard test.
Objective: To evaluate the performance of cistatin/creatinine based equations for estimating renal function in patients with SLE.
Methods: We conducted two phases: the first phase included 14 patients in which iothalamate clearance was used to determine the glomerular filtration rate (GFR) and compared with different equations based on cystatin C and/or creatinine. In the second phase, we used the best equation (a cystatin and creatinine-based equation) as "reference standard" to compare 5 creatinine-based equations in 55 patients with SLE.
Results: In the first phase the equation developed by Stevens and colleagues (based on creatinine and cystatin C), was the best equation. In phase 2, the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation was the best equation with bias of -2. 1 ml/min/1.73, accuracy (P30) of 94.5% and precision (interquartile range of differences) of -2.1 ml/min/1.73.
Conclusions: Our data suggest that CKD-EPI is the best creatinine-based equation to estimate GFR in patients with SLE.