Reliability of routine clearance methods for assessment of glomerular filtration rate in advanced renal insufficiency

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Abstract
The reliability of different clearance methods to assess the glomerular filtration rate (GFR) was tested in fifteen patients with advanced chronic renal failure (range of GFR: 3–13 ml/min). The renal [51Cr]EDTA plasma clearance (Er) measured during optimal conditions with determination of residual bladder-urine was used as reference parameter of GFR, the reliability being ± 1.1 ml/min. The clearances of all the studied methods turned out to overestimate GFR. In the following the value by which a measured clearance value is subtracted to give an accurate estimate of GFR and the reliability (±) of a thus corrected value to assess GFR of the individual patient are given in parenthesis. The arithmetic mean of the renal plasma clearances of endogenous creatinine (Clcreat) and urea (2.0 ml/min; ±1.5 ml/min); single determination of 24-h Clcreat (3.4 ml/min; ± 2.0 ml/min); Clcreat calculated from a measured plasma creatinine concentration, considering sex, age and body weight of the patient (2.9 ml/min; ± 2.3 ml/min); total [51Cr]EDTA plasma clearance (Et) determined from three blood samples drawn 3–5 h after i.v. single injection (3.7 ml/min; ± 2.2 ml/min); and Et determined from two blood samples drawn 4 and 24 h after i.v. injection (0.5 ml/min; ± 0.5 ml/min). It is concluded that the most reliable assessment of GFR (=Er) is achieved either from a direct measurement or indirectly from Et determined from two blood samples drawn 5 and 24 h after i.v. single injection. Use of the mean value of three 24-h Clcreat determinations is recommended if facilities for measurement of radioactivity are not available.

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