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.
51Cr-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 m2,
compared with 44 mL/min/1.73 m2 for serum creatinine.
Conclusion: Serum cystatin C is a simple and sensitive screening test
for kidney dysfunction in older people.
