An efficient approach for glomerular filtration rate assessment in older adults

AIMS Assessment of glomerular filtration rate (GFR) is crucial because the GFR value defines the stage of chronic kidney disease and determines the adjustment of drug dosage. The aim was to investigate a new method for the accurate determination of GFR in older adults based on the combination of an exogenous filtration marker, iohexol, and an endogenous marker, serum creatinine or cystatin C. METHODS We combined variables for the estimation of GFR with a reduced set of measurements of the marker iohexol. In a population-based sample of 570 subjects (>= 70 years old) from the Berlin Initiative Study (BIS), we investigated the following: (i) the BIS1 and BIS2 equations based on age, gender and serum creatinine with or without serum cystatin C; (ii) equations based on one or two iohexol measurements; and (iii) equations based on the combination of variables from BIS1 or BIS2 with iohexol measurements. The reference standard was based on eight iohexol measurements. The cut-off value of 60 ml min(-1) (1.73 m)(-2) was chosen to assess accuracy. Equations were constructed using a learning sample (n = 285) and an independent validation sample (n = 285). RESULTS Misclassification rates were 17.2% (BIS1), 11.6% (BIS2), 14.7% [iohexol measurement at 240 min (iohexol(240))], 7.0% (iohexol(240) combined with variables included in BIS1) and 6.7% (iohexol(240) combined with variables included in BIS2). Misclassification rates did not decrease significantly after inclusion of two or three iohexol measurements. CONCLUSIONS Combined strategies for the determination of GFR lead to a relevant increase of diagnostic validity.