Background: Conventional estimates of glomerular dysfunction, including serum creatinine and creatinine clearance, are inadequate in older people. In this study we have compared the diagnostic accuracy of a novel test of kidney disease, cystatin C, against these markers in older patients with a range of renal function.
Methods: Fifty-three patients (mean age 79.6 years, range 69-92 years) with a variety of medical diagnoses were recruited via outpatient clinics. Exclusion criteria included active rheumatoid disease, known current malignancy, renal replacement therapy/renal transplantation and cognitive impairment. (51)Cr-EDTA was used as the reference method against which the other markers of glomerular filtration rate were compared using regression analyses.
Results: The best fit with glomerular filtration rate was given by Cockcroft and Gault calculated clearance (R(2) = 0.83), followed by serum cystatin C (R(2) = 0.79), serum creatinine (R(2) = 0.76) and creatinine clearance (R(2) = 0.73). The accuracy for glomerular filtration rate prediction was poor for all markers. Serum cystatin C detected nearly all patients with mild renal impairment whereas serum creatinine only detected half of these cases. Regression modelling predicted that the upper limit of normal for serum cystatin C would be exceeded as glomerular filtration rate fell below 64 mL/min/1.73 m(2), compared with 44 mL/min/1.73 m(2) for serum creatinine.
Conclusion: Serum cystatin C is a simple and sensitive screening test for kidney dysfunction in older people.