Chronic kidney disease has been defined in terms of creatinine-based estimated glomerular filtration rate (GFR). This study examines an alternative serum measure of kidney function, cystatin C. The researchers' goal was to determine whether elevated cystatin C concentrations in patients with normal estimated GRF could define a state of “preclinical” kidney disease. Data were collected from 4,663 elderly persons (3,659 without known kidney disease) taking part in a community-based longitudinal study of adults 65 years of age and older. Comparing the ability of creatinine, estimated GFR and cystatin C to distinguish mortality risk among persons with chronic kidney disease, the authors found that elevated cystatin C concentrations were associated with incrementally increasing mortality risk. After adjustment for traditional risk factors, prevalent stroke, heart failure, coronary heart disease and C-reactive protein level, the persons with no chronic kidney disease and high cystatin C levels had statistically significantly increased risk for each outcome compared with the persons with no chronic kidney disease and low cystatin C levels.
One limitation of the study is its inability to determine the extent to which cystatin C may be influenced by nonrenal factors, because this study did not directly measure GFR or albuminuria and participants with albuminuria might have been misclassified as having no kidney disease. In addition, the researchers did not find out whether thyroid dysfunction could have influenced the study, because measures of thyroid-stimulating hormone were available only in about half the cohort at the 1989-90 visit. Overall, these results imply that among elderly persons, cystatin C concentration may be a better biomarker for adverse outcomes than serum creatinine concentration.