Estimating the glomerular filtration rate using serum cystatin C levels in patients with spinal cord injuries

Study design: Prospective cohort study. Objectives: To investigate the relationship between (51)chromium-ethylene-diamine-tetra-acetate (Cr-51-EDTA) clearance, serum cystatin C (CysC), serum creatinine, creatinine clearance and estimated glomerular filtration rate (eGFR(MDRD), MDRD stands for modification of diet in renal disease) based on the serum creatinine in patients with complete or incomplete spinal cord injury (SCI) and to develop and evaluate a GFR-estimating equation using serum CysC. Settings: Spinal Cord Injury Unit, Viborg Regional Hospital, Viborg, Denmark. Methods: Ninety-eight men and 47 women with SCI were included in the study. Serum CysC levels were measured by an automated particle-enhanced nephelometric immunoassay, serum and urine creatinine levels were measured by an enzymatic method traceable to the IDMS creatinine reference method, and Cr-51-EDTA clearance was measured by a multiple plasma sample method. Results: The area under the curves (AUCs) in the non-parametric receiver operating characteristics (ROC) plots for serum CysC were compared with serum creatinine and to eGFRMDRD and revealed a significant difference (P-value<0.05) for all SCI patients. There was no significant difference between the AUC for serum CysC compared with the AUC for creatinine clearance. GFR (ml min(-1) per 1.73 m(2)) can be calculated from serum CysC values (mg l(-1)) using the equation eGFR(CysC) 212 . exp(0.914 . CysC). The model accurately predicted the GFR of 88% of patients within +/- 30% of the measured GFR, and it was able to predict the GFR of 50% of patients within +/- 10% of the measured GFR. Conclusion: In patients with SCI, GFR can be estimated independent of age, sex and muscle mass by a newly developed equation based on a single serum CysC value. Spinal Cord (2012) 50, 778-783; doi:10.1038/sc.2012.52; published online 1 May 2012