Prediction of urinary excretion of technetium-99m-MAG3.
The urinary excretion of 99mTc-mercaptotriacetylglycine (MAG3), like that of 131I-orthoiodohippurate (OIH), can be used to identify acute renal transplant rejection and measure its severity. This parameter is often quantitated as the excretory index (observed excretion/predicted excretion). A new method for predicting the urinary excretion of 99mTc-MAG3 is presented.


METHODS
The expected excretion was calculated from multisample plasma time-activity curves in 122 subjects, with correction for the first pass of the initial bolus. The resulting formula was tested prospectively against actual urine measurements in an additional 466 subjects.


RESULTS
Least-squares fitting led to the following equation: Predicted excretion = 0.79(1-exp(-0.0066CMAG3), with residual s.d. 0.06, where CMAG3 is MAG3 clearance in ml/min and the predicted excretion is expressed as a fraction of the administered dose. Tested prospectively in the additional 466 subjects, the s.d. was 0.09.


CONCLUSIONS
A new formula to predict the urinary excretion of 99mTc-MAG3 has been developed and prospectively validated. Based on our data, the normal range for the excretory index using MAG3 is the same as that of 131I-OIH, 0.8-1.2.
University of Alabama Hospital and VA Medical Center, Birmingham, USA.
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Russell
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Dubovsky
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Taylor
D000328:Adult; D006084:Graft Rejection / Q000000981:diagnostic imaging / Q000652:urine*; D006801:Humans; D007457:Iodine Radioisotopes / Q000652:urine; D007465:Iodohippuric Acid / Q000493:pharmacokinetics; D016030:Kidney Transplantation / Q000000981:diagnostic imaging*; D019520:Living Donors; D011446:Prospective Studies; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000652:urine*; D017263:Technetium Tc 99m Mertiatide / Q000652:urine*
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D007465:Iodohippuric Acid; D017263:Technetium Tc 99m Mertiatide