Diagnostic Efficiency of Cystatin C and Serum Creatinine as Markers of Reduced Glomerular Filtration Rate in the Elderly

This is a secondary analysis of data from a cross-sectional study to evaluate the diagnostic efficiency of cystatin C as a marker of the glomerular filtration rate in the elderly. Thirty patients (15 male, 15 female, mean age 75.4 +/- 7.1 years) attending a geriatric ward were enrolled. Exclusion criteria were previously diagnosed renal disease, dementia and heart failure (NYHA III or IV). Cystatin C in serum was determined by a particle-enhanced turbidimetric assay. Inulin clearance was assessed using a single-shot method. Also, Cockcroft-Gault formula was calculated. Twelve patients had a reduced glomerular filtration rate (<70 ml/min/ 1.73 m(2)). The mean values were 88.4 mu mol/l(+/- 27.7) for serum creatinine, 1.57 mg/l(+/- 0.34) for cystatin C and 88.7 ml/min/1.73 m(2) (+/- 34.6) for inulin clearance. Maximum efficiency was 0.73 for serum creatinine (cut-off limit 82 mu mol/l), 0.67 for cystatin C (cut-off limit 1.63 mg/l) and 0.8 for Cockcroft and Gault estimation (cut-off limit 54 ml/min/1.73 m(2)). A receiver operating characteristics (ROC) analysis did not show any differences between the various methods. Therefore, cystatin C in serum may not improve the diagnostic efficiency in detecting a reduced glomerular filtration rate in the elderly. Furthermore, normal ranges for serum creatinine in the elderly might need to be adjusted.