In determining the glomerular filtration rate (GFR)or creatinine clearance,a 24-hour urine is obtained.If a reliable 24-hour urine collection is not possible,

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Historically,timed 24-hour urine collections have been used to evaluate GFR or creatinine clearance.If a reliable 24-hour urine collection is not possible,the Cockcroft and Gault formula may be used to determine the creatinine clearance from a serum creatinine value.The BUN level is not a reliable indicator of kidney function because the rate of protein metabolism is not constant.An increased BUN/creatinine ratio is typically noted with prerenal conditions,but does not provide an estimate of GFR.

In Determining the Glomerular Filtration Rate (GFR)or Creatinine Clearance,a 24-Hour