How is renal function assessed in patients with azotemia?

Updated: Apr 24, 2020
  • Author: Moro O Salifu, MD, MPH, FACP; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Answer

Radionuclide assessment of the GFR is the best available test for measuring kidney function. However, this test is expensive and not widely available, and as a result, serum creatinine concentration and creatinine clearance (CrCl) more commonly are used to estimate GFR.

An inverse relation between serum creatinine and the GFR exists; however, serum creatinine and CrCl are not sensitive measures of kidney damage, for 2 reasons. First, substantial renal damage can take place before any decrease in the GFR occurs. Second, a substantial decline in the GFR may lead to only a slight elevation in serum creatinine (see the image below). Because of compensatory hypertrophy and hyperfiltration of the remaining healthy nephrons, an elevation in serum creatinine is apparent only when the GFR falls to about 60-70 mL/min.

Graph shows relation of glomerular filtration rate (GFR) to steady-state serum creatinine and blood urea nitrogen (BUN) levels. In early renal disease, substantial decline in GFR may lead to only slight elevation in serum creatinine. Elevation in serum creatinine is apparent only when GFR falls to about 70 mL/min.

Graph shows relation of glomerular filtration rate Graph shows relation of glomerular filtration rate (GFR) to steady-state serum creatinine and blood urea nitrogen (BUN) levels. In early renal disease, substantial decline in GFR may lead to only slight elevation in serum creatinine. Elevation in serum creatinine is apparent only when GFR falls to about 70 mL/min.

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