The utility of 99mTc-mercaptoacetyltriglycine in captopril renography.

99mTc-Mercaptoacetyltriglycine (MAG3) is a new 99mTc renal radiopharmaceutical with properties similar to orthoiodohippurate (OIH). 99mTc-MAG3 is highly protein bound and is efficiently extracted by the proximal tubules. While the clearance is only 50 to 65% that of OIH, the plasma concentration is higher and the rates at which the two tracers appear in the urine are almost identical. Studies comparing 99mTc-MAG3 and OIH in animals with renovascular hypertension (RVH) show comparable results. Preliminary studies comparing 99mTc-MAG3 renography with angiography in hypertensive patients show promising results and suggest 99mTc-MAG3 will probably have a sensitivity and specificity for detecting RVH similar to OIH. The optimal criteria for defining an abnormal study still need to be determined and then applied in a prospective study.