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

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 (E_r) 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 (Cl_creat) and urea (2.0 ml/min; ±1.5 ml/min); single determination of 24-h Cl_creat (3.4 ml/min; ± 2.0 ml/min); Cl_creat 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 (E_t) determined from three blood samples drawn 3–5 h after i.v. single injection (3.7 ml/min; ± 2.2 ml/min); and E_t 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 (=E_r) is achieved either from a direct measurement or indirectly from E_t determined from two blood samples drawn 5 and 24 h after i.v. single injection. Use of the mean value of three 24-h Cl_creat determinations is recommended if facilities for measurement of radioactivity are not available.

Key Words:

• [⁵¹Cr]EDTA plasma clearance
• endogenous creatinine clearance
• glomerular filtration rate
• plasma creatinine concentration
• uraemia
• urea clearance