Glomerular filtration rate measurement: a neglected test in urological practice.

OBJECTIVES

To assess the accuracy and reproducibility of methods used to measure glomerular filtration rate (GFR) in clinical practice.

PATIENTS AND METHODS

Simultaneous clearances of iohexol, 99mTc-diethylene-triamine-penta-acetic acid (DTPA), 24 h renal creatinine clearance and creatinine clearance estimated from a serum sample only, were obtained in 31 patients. Accuracy was calculated relative to iohexol clearance. The reproducibility of each method was determined by repeat measurements in the same individuals: three 99mTc-DTPA clearances in 21 patients; three 24 h creatinine clearance estimations in 12 patients; and three serum creatinine clearance estimations in 21 patients.

RESULTS

The mean differences between 99mTc-DTPA clearance, 24 h renal creatinine clearance and estimated creatinine clearance compared with the reference method were 0.2 mL/min, 21.6 mL/min and 0.6 mL/min, respectively. 99mTc-DTPA clearance had fairly tight 95% limits of agreement (12.2 mL/min) compared with 35.4 mL/min for 24 h creatinine clearance and 25.8 mL/min for estimated creatinine clearance. The reproducibility for each method was 5.4%, 24.3% and 6.1%, respectively.

CONCLUSION

Single-injection 99mTc-DTPA clearance provides an accurate and reproducible method of GFR measurement that is suitable for objective monitoring of renal function. Twenty-four hour creatinine clearance is neither sufficiently accurate nor reproducible for this purpose. Creatinine clearance estimation from a serum sample without urine collection may be preferable to the more traditional 24 h collection method.