Clarifying the fog of natural and man made renal function tests
John G. Toffaletti
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This article has been reformatted to fit the layout of the website Reproduced with permission from POINT OF CARE: The Journal of Near-Patient Testing & Technology. 10(1):45-50, March 2011, Toffaletti, JG: ‘Clarifying the Fog of Natural and Manmade Renal Function Tests: Creatinine, Clearances, Glomerular Filtration Rate, and Estimated Glomerular Filtration Rate’.
All copyrights belong to the Journal "Point of Care" http://journals.lww.com/poctjournal/pages/default.aspx and publisher Lippincott Williams & Wilkins.
ABSTRACT: This review addresses common misconceptions about serum creatinine, glomerular filtration rate (GFR) measured by either clearance tests (creatinine, iothalamate, inulin, etc) or by equations that calculate the estimated GFR (eGFR), the perceived benefit of isotope-dilution mass spectrometry standardization of creatinine methods, and the accurate definition of “clearance.” Creatinine, especially within-individual monitoring, is a good renal function test that is a better early indicator of diminishing renal function than often believed. Because of its wide population variation, the measured GFR by “clearance” may be no better than serum creatinine for detecting early clinical changes in chronic kidney disease. The eGFR equations intended to calculate GFR (Modification of Diet in Renal Disease eGFR and Chronic Kidney Disease Epidemiology Collaboration eGFR) are measures of serum creatinine adjusted for age, sex, and race, with various mathematical manipulations included to produce an average numerical agreement with the GFR, yet both equations produce widely scattered comparisons between eGFR and measured GFR. Thus, eGFR would be more clinically useful if interpreted simply as a normalized serum creatinine.
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