Laboratory evaluation of kidney function in the elderly1

Abstract

Abstract Demographic changes and the increasing proportion of elderly among the overall population call for consideration of the morphology and function of the ageing kidney. Its hallmarks include progressive loss of kidney function reserve and potential for compensation. Differentiation from true kidney disease and/or injury is important, since early diagnosis allows for treatment that may delay progression of renal disease in the elderly. The glomerular filtration rate (GFR) is the recommended laboratory parameter to describe glomerular function of the kidney and hence to distinguish the different stages of chronic renal diseases. Current discussions focus on estimated GFR formulas based on endogenous substances (creatinine and cystatin C). Unfortunately, these estimated GFR formulas were not specifically developed for the aged population and reference ranges for a normal renal function are not defined beyond the age of 70 years. There are inconsistencies between data sets of formulas depending on age and disease. No methods have been validated for determination of glomerular and tubular renal function in the elderly. Until the validation of estimated GFR formulas or new biomarkers, one relies on formulas tested and additional renal and non-renal laboratory parameters. These should be applied according to recent physical findings. Age, disease and ongoing therapy should influence the selection of a formula with the least deviation from the gold standard (exogenous clearance). The consistent use of standardised methods and calibrators will advance the estimation of renal function in the elderly. The initial assessment of the ageing kidney remains a challenge with the risk of both over- and underestimating kidney function. Follow-up investigation is essential to monitor changes from individual baseline kidney function. The main goal of current and future studies will be the individual assessment of kidney function in the elderly considering its functional reserve.