Background: The aim of this study was to assess the accuracy and precision of estimators of true glomerular filtration rate (GFR) (Cockcroft formula, measured creatinine clearance (CCR) and a cystatin-C-based estimation) in elderly patients attending a geriatric department. Additionally, parameters influencing GFR in the elderly were evaluated. Methods: 30 patients aged 57–90 years treated in the Geriatric Department for pulmonary or cerebral diseases were included in the study. Nine patients were diabetic and 16 hypertensive. Exclusion criteria were advanced dementia, acute heart failure and primary renal disease. Inulin clearance (CINU), CCR and estimation by Cockcroft-Gault equation (CG) were performed on the same day. For comparison of the methods an analysis according to Bland and Altman was used, depicting the mean difference between the methods and the limits of agreement of the differences, representing their 95% interval of confidence. Furthermore, the influence of confounding variables on GFR estimation was analyzed by multiple regression. Results: Baseline characteristics showed a median age of 74.5 years and a median body weight of 66.7 kg. Median values for serum creatinine 88.4 µmol/l, 5.74 mmol/l for urea and 1.57 mg/l for cystatin C. CCR (median: 51.6 ml/min) and CG (median: 63.0 ml/min) underestimated CINU (median: 83.3 ml/min). Both methods showed poor precision compared with CINU. The upper limit of agreement of the difference was 101.3 ml/min for CCR and 81.4 ml/min for CG, the lower limit was –33.8 ml/min for CCR and –24.6 ml/min for CG. Among frequently used variables to predict GFR, the reciprocal of serum creatinine and body weight revealed a significant influence but not age or gender. A cystatin-C-based estimation of GFR, derived from regression analysis, did not improve the precision of the estimation of GFR compared to CG. Additionally, the occurrence of diabetes mellitus disclosed a borderline influence on the estimation of GFR. Conclusion: CCR is not only inconvenient and time consuming, but also imprecise and inaccurate in the elderly, mainly due to reduced muscle mass and erroneous urine sampling. CG and a cystatin-C-based estimation are slightly more adequate, but overall there is no sufficiently precise formula for GFR estimation in the elderly.
Aims: To evaluate the quality of bedside estimation of glomerular filtration rate (GFR) in hospitalized elderly patients. Methods: We evaluated common estimators of GFR in 29 women and 32 men aged 60 and older hospitalized in a geriatric ward: creatinine clearance (CCR), the Cockcroft-Gault formula (CG), the modification of diet in renal disease formula (MDRD), Baracskay formula (BAR), and a newly developed formula derived recently by us (GCM). Inulin clearance (CINU) was used to assess GFR. Exclusion criteria were mental illness and urinary incontinence. Results: According to Bland and Altman accuracy and precision of all estimators were low and there was an underestimation of actual GFR: CCR 38.9 ml/min; CG 39.7 ml/min; MDRD 19.8 ml/min; BAR 34.0 ml/min, and GCM: 24.7 ml/min. The accuracy and precision of all methods were even lower in patients with a GFR of >90 ml/min and in patients with diabetes. In receiver-operating characteristics (ROC analysis) all formulas were superior to serum creatinine and overall MDRD disclosed the best results in detecting both a GFR of <90 ml/min and <60 ml/min. Conclusions: In general, estimation errors are large in an acute care setting. However, formula estimation is clearly superior to serum creatinine and CCR. MDRD gave the best results but may be replaced by the more simple CG and GCM formulas, whereas BAR was inferior.
This is a secondary analysis of data from a cross-sectional study to evaluate the diagnostic efficiency of cystatin C as a marker of the glomerular filtration rate in the elderly. Thirty patients (15 male, 15 female, mean age 75.4 +/- 7.1 years) attending a geriatric ward were enrolled. Exclusion criteria were previously diagnosed renal disease, dementia and heart failure (NYHA III or IV). Cystatin C in serum was determined by a particle-enhanced turbidimetric assay. Inulin clearance was assessed using a single-shot method. Also, Cockcroft-Gault formula was calculated. Twelve patients had a reduced glomerular filtration rate (<70 ml/min/ 1.73 m2). The mean values were 88.4 micromol/l (+/- 27.7) for serum creatinine, 1.57 mg/l (+/- 0.34) for cystatin C and 88.7 ml/min/1.73 m2 (+/- 34.6) for inulin clearance. Maximum efficiency was 0.73 for serum creatinine (cut-off limit 82 micromol/l), 0.67 for cystatin C (cut-off limit 1.63 mg/l) and 0.8 for Cockcroft and Gault estimation (cut-off limit 54 ml/min/1.73 m2). A receiver operating characteristics (ROC) analysis did not show any differences between the various methods. Therefore, cystatin C in serum may not improve the diagnostic efficiency in detecting a reduced glomerular filtration rate in the elderly. Furthermore, normal ranges for serum creatinine in the elderly might need to be adjusted.
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