Estimation of absolute renal uptake with technetium-99m dimercaptosuccinic acid: direct comparison with the radioactivity of nephrectomy specimens

context and objective: studies using radionuclides are the most appropriate method for estimating renal function. dimercaptosuccinic acid chelate labeled with technetium-99m (99mtc-dmsa) is the radiopharmaceutical of choice for high-resolution imaging of the renal cortex and estimation of the functional renal mass. the aim of this study was to evaluate a simplified method for determining the absolute renal uptake (aru) of 99mtc-dmsa prior to nephrectomy, using the radioactivity counts of nephrectomy specimens as the gold standard. design and setting: prospective study at the division of nuclear medicine, department of radiology, universidade estadual de campinas. methods: seventeen patients (12 females; range 22-82 years old; mean age 50.8 years old) underwent nephrectomy for various reasons. renal scintigraphy was performed three to four hours after intravenous administration of a mean dose of 188.7 mbq (5.1 mci) of 99mtc-dmsa, which was done six to 24 hours before surgery. the in vivo renal uptake of 99mtc-dmsa was determined using the radioactivity of the syringe before the injection (measured using a dose calibrator) and the images of the syringe and kidneys, obtained from a scintillation camera. after surgery, the reference value for renal uptake of 99mtc-dmsa was determined by measuring the radioactivity of the nephrectomy specimen using the same dose calibrator. results: the aru measurements were very similar to those obtained using the reference method, as determined by linear regression (r-squared = 0.96). conclusion: aru estimation using the proposed method before nephrectomy seems to be accurate and feasible for routine use.