Serum creatinine is the most commonly used screening test for renal failure. We hypothesized that serum creatinine would underestimate the degree of renal failure in elderly people because they have a reduced muscle mass. If so, this would lead to underrecognition and thus suboptimal care of patients with severe renal failure.
We conducted a retrospective medical record review of all patients 65 years or older in an outpatient academic family medicine practice. The glomerular filtration rate was calculated using the Cockcroft and Gault formula and was used to evaluate the testing characteristics of serum creatinine for the detection of renal failure.
We screened 1510 patients, 854 (56.6%) of whom met the inclusion criteria. Renal failure (glomerular filtration rate, ≤50 mL/min) was present in 28.9% of the patients, and severe renal failure (Cockcroft and Gault formula glomerular filtration rate, ≤30 mL/min) was present in 6.4%. A serum creatinine level of greater than 1.7 mg/dL (>150 µmol/L) had a sensitivity of 12.6% and a specificity of 99.9% for the detection of renal failure. For the detection of severe renal failure, the sensitivity was 45.5%, with a 99.1% specificity. Only 15 (27.3%) of the 55 patients with severe renal failure were referred to a nephrologist. Moreover, 34 (85%) of the 40 nonreferred patients with severe renal failure were incompletely evaluated regarding the metabolic complications associated with kidney dysfunction.
Serum creatinine is a poor screening test for renal failure in elderly patients, leading to marked underinvestigation and underrecognition of renal failure in this population.