Magnitude of underascertainment of impaired kidney function in older adults with normal serum creatinine

Objectives: To estimate in a community-dwelling elderly population the magnitude of renal function misclassification, occurring when persons with normal serum creatinine have reduced glomerular filtration rate (GFR), and to describe the participant characteristics related to misclassification. Design: Cross-sectional. Setting: Population-based study of older Italian people. Participants: Six hundred sixty participants aged 65 to 92 with normal serum creatinine. Measurements: GFR was estimated using the Cockcroft-Gault equation and creatinine clearance (CrCl) calculated from 24-hour urine collection. Results: In participants with normal serum creatinine, 39% and 25% had moderate renal function impairment (GFR < 60 mL/min) according to the Cockcroft-Gault equation and CrCl calculation, respectively. Prevalence of moderate renal impairment in those aged 65 to 74, 75 to 84, and 85 and older was 18.6%, 58.3%, and 96.8%, respectively (P for trend <.001) according to the Cockcroft-Gault equation, and 15%, 35.7%, and 58.7%, respectively (P for trend <.001) based on the CrCl calculation. In addition, female sex (P <.001) and normal or underweight (P <.05) were factors associated with high risk of misclassification. Conclusion: Serum creatinine alone is one of the most widely used methods of assessing renal function in clinical practice despite its well-known poor correlation with GFR. A large proportion of older persons with impaired renal function are not diagnosed if clinicians rely solely on normal serum creatinine as evidence of normal renal function. Opportunities may be missed for slowing progression of kidney disease, managing comorbidities and complications related to renal impairment, and adjusting drug dosage for renal function.