Glomerular filtration rate in adults a single sample plasma clearance method based on the mean sojurn time

Sammanfattning: Glomerular filtration rate (GFR) is a key parameter in evaluating kidney function. After a bolus injection of an exogenous GFR marker in plasma an accurate determination of GFR can be made by measuring the marker concentration in plasma during the excretion. Simplified methods have been developed to reduce the number of plasma samples needed and yet still maintain a high accuracy in the GFR determination. Groth previously developed a single sample GFR method based on the mean sojourn time of a GFR marker in its distribution volume. This method applied in adults using the marker 99m Tc-DTPA is recommended for use when GFR is estimated to be ? 30 mL/min. The aim of the present study was to further develop the single plasma sample GFR method by Groth including patients with severely reduced renal function and different GFR markers. Three different GFR markers 51Cr-EDTA, 99mTc-DTPA and iohexol were investigated. Formulas were derived for the markers 51Cr-EDTA and iohexol when GFR is estimated to be ? 30 mL/min. For patients with an estimated GFR < 30 mL/min a special low clearance formula with a single sample obtained about 24 h after marker injection was developed. The low clearance formula was proven valid for use with all three markers. The sources of errors and their influence on the calculated single sample clearance were investigated. The estimated distribution volume is the major source of error but its influence can be reduced by choosing a suitable sampling time. The optimal time depends on the level of GFR; the lower GFR the later the single sample should be obtained. For practical purpose a 270 min sample is recommended when estimated GFR ? 30 mL/min and a 24 h sample when estimated GFR < 30 mL/min. Sampling at 180 min after marker injection may be considered if GFR is estimated to be essentially normal.