Determination of glomerular filtration rate by means of newly developed plastic scintillation counter both with and without dilution procedures.

Abstract

The double-well single-plastic scintillation counter (DW counter) has been developed to reduce the need for technical expertise in a plasma sample method after a single injection of radioactive marker. The DW counter serves the 2 functions of a standard well counter in well A and a dose calibrator in well B. The aim of this study was to assess the clinical feasibility of the counter for the estimation of glomerular filtration rate (GFR) with (99m)Tc-diethylenetriaminepentaacetic acid (DTPA). The study was performed on 25 patients with varying degrees of renal dysfunction. The GFR was estimated by a single-sample method after a single injection of (99m)Tc-DTPA. Total injected dose and plasma radioactivity were calculated following 2 methods: standard dilution with a single well (dilution method) and no dilution with 2 wells (direct method). The GFR directly estimated by the DW counter correlated excellently with the GFR estimated by the dilution method (r = 0.998; root mean square error = 2.01 mL/min/1.73 m(2)). The 95% of differences (-0.3124 to 0.0423 percentage injected dose [%ID]/L/1.73 m(2)) in plasma concentration between the 2 comparative methods was <2 SDs. The direct method tended to give slightly higher readings of plasma concentration than did the dilution method (95% confidence interval = -0.0364 to -0.0904 %ID/L/1.73 m(2)). The DW counter can circumvent laborious dilution techniques and expertise required for quantifying the GFR in a single-sample method after a single injection of (99m)Tc-DTPA in clinical practice. It is proposed as an alternative to the standard dilution method.