Reassessment of the reproducibility of Technetium-99m mercaptoacetyltriglycine clearance.

Conflicting results have been published concerning the reproducibility of Tc-99m MAG3 clearance. The aim of the study was to reevaluate again this reproducibility on a large prospective series of healthy volunteers. Fifty subjects underwent three successive tests performed at 1-week interval. The physiological conditions were controlled as much as possible and all experimental measurements were rigorously double-checked. Renal clearances were calculated using single sample algorithms. Thin layer chromatography demonstrated a radiochemical purity of more than 92% (mean 93.8%; SD 1.6%; range 92.0-96.4%). The mean (and SD) of 44th minute plasma concentrations for the three successive measurements were respectively 1.8 +/- 0.4, 2.1 +/- 0.4 and 1.9 +/- 0.4 (%dose/liter). The mean changes (and S.D. of differences) between two tests were 0.26 +/- 0.29, -0.08 +/- 0.5 and 0.18 +/- 0.30 respectively between tests 1 and 2, tests 1 and 3, and tests 2 and 3. Using Bubeck's algorithm, the mean clearance values (ml/min/1.73 m2) were 268.8 (range 201.4-336.8), 247.2 (range 170.5-290.3), and 262.8 (range 187.4-340.0) respectively for the first, second and third measurements. Using Russell's approach, the mean clearance values were respectively 314.9 (range: 208.7-441.7), 280.1 (range: 167.5-358.6), and 305.4 (range: 189.5-447.9). High differences were observed between the 3 tests. Using Russell s formula, the SD of differences between two tests was respectively 35.8, 47.7 and 57.7 ml/min/1.73 m2 between tests 1 and 2, tests 1 and 3, and tests 2 and 3. Whether such a large variability is acceptable in clinical practice depends solely on what the clinician is expecting.