Differences in the glomerular filtration rate calculated by two creatinine-based and three cystatin-C-based formulae in hospitalized elderly patients

Background: Reduced renal function is a health problem in elderly patients. Different creatinine- and cystatin-C-based formulae have been used to estimate glomerular filtration rate (GFR). Aims: To investigate individual and group differences of GFR estimates derived from five different formulae. Methods: 60 patients were randomly assigned to participate in this cross-sectional study. Nutrition status was assessed, blood samples were drawn and GFR was calculated using two creatinine- and three cystatin-C-based formulae. Results: Four of five formulae indicate reduced GFR in >70% of the participants, GFR was significantly less in malnourished patients according to one creatinine formula. Estimates from the formulae were highly correlated (r = 0.607-0.863, p < 0.001), but individual differences were between -36.1 and 79.9 ml/min/1.73 m². The formulae grouped 38.3-60.0% of the subjects differently into the five stages of chronic kidney disease. BMI, total cholesterol, age and gender were significant predictors for the calculated GFR differences between the formulae. Conclusion: The prevalence of reduced renal function is high in elderly hospitalized patients. BMI, age and/or gender can affect GFR estimates depending on the formula used, and there is an association between total cholesterol and calculated GFR differences between formulae. Different formulae can result in a different grouping of patients into the five stages of chronic renal disease.