Assessment of renal function is important. The gold-standard marker is glomerular filtration rate (GFR) measured by inulin clearance normalized to a standard body surface area of 1.73 m2. Inulin, no longer available in North America, has been replaced by nuclear medicine tests such as 51Cr EDTA, 99mTc DTPA and iothalamate clearances. The use of serum creatinine as a surrogate endogenous marker is hampered by height, gender and muscle mass variability,substantial tubular secretion in advanced renal failure and non-standardized measurements. The limitations of creatinine can be reduced when applying height/creatinine ratios with gender and age-dependent constants that have to be established for each center. The small molecular weight protein cystatin CysC shows a significantly better diagnostic performance for the detection of impaired GFR than serum creatinine. It also does not undergo tubular secretion in chronic renal failure, nor does it show significant non-renal elimination. Its concentration falls in the first year of life with the rise of GFR and remains constant thereafter until 60 years of age in both sexes. GFR can be estimated reliably with a recently published formula without the need for any additional anthropological data. CysC allows for reliable estimation of GFR in children.
Keywords: Glomerular filtration rate, iothalamate clearance, 99Tc DTPA clearance, 51Cr EDTA clearance, creatinine, Schwartz formula, cystatin C
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