Captopril MAG3/DTPA Renal Scintigraphy can determine overall renal (kidney) function and also relative left and right kidney function. The test is performed using the radiotracer called Tc99m-DTPA (Diethylene Triamine Pentacaetic Acid) or Tc99m-MAG3 (Mercaptoacetyltriglycine). The test is often used in combination with a diuretic drug such as frusemide to determine if a kidney is obstructed. This scan is also used to look for narrowing of the renal arteries as a cause of high blood pressure (hypertension). It is often combined with a type of anti-hypertensive drug known as an angiotension-converting enzyme inhibitor (ACEI) for this purpose. The scan can also be very useful in assessing the function of renal transplant grafts.