Renal depth estimates to improve the accuracy of glomerular filtration rate

This study was performed to validate a computer implementation of the Gates' method for radionuclide glomerular filtration rate (RGFR) calculation. The accuracy of the original method was improved by replacing the Tonnesen formula that estimated renal depth with direct measurement from lateral views to calculate tissue attenuation correction.

Both the creatinine clearance test (CCT) and dynamic 99mTc-diethylenetriamine pentaacetic acid (DTPA) renal scintigraphy (DRS) were performed on 38 patients on the same day. RGFR was quantified from the attenuation corrected absolute DTPA uptake of the kidneys on DRS from 120-180 sec after injection. Attenuation correction was estimated using the lateral views of the kidneys taking in account the distance from the computed geometric center of the kidneys to the posterior body surface along a line vertical to the collimator surface. CCT and glomerular filtration rate estimates from DRS were compared by linear regression.

RGFR estimates agreed well with CCT, yielding a correlation coefficient of 0.92 in 38 patients and 0.90 in a subgroup of 11 patients suffering from chronic renal failure.

Present modifications improve RGFR accuracy to the precision range of blood sample based methods. This modified method requires little additional work and no extra cost in patients undergoing DRS. RGFR calculation may be advantageous in cases when 24-hr urine collection for CCT cannot be obtained, and it should improve the accuracy of the captopril test.