MAG3/DTPA diuretic renogram: kidney drainage and function

What are MAG3 and DTPA?

A MAG3 or DTPA renogram is a nuclear medicine test that shows how the kidneys clear an injected substance and how urine drains from the kidney into the ureter. A small amount of a radioactively labeled substance is injected into a vein, and a camera follows its passage through the kidneys minute by minute. A diuretic medicine (furosemide) is injected to speed up urine flow.

MAG3 and DTPA are two different radiopharmaceuticals used for the same purpose, and the test is done the same way with either. MAG3 is taken up better by the kidney, so it gives more accurate results in babies and when kidney function is poor. Centers that do not have MAG3 use DTPA, and the result is interpreted the same way.

What does it show?

• the share of each kidney in total function (normally about 45–55%),
• drainage: whether urine flows easily from the kidney or is delayed,
• whether there is a blockage, especially in UPJ obstruction and megaureter.

When is it done?

• in moderate and severe hydronephrosis,
• when dilation increases during follow-up,
• to help decide on surgery,
• to check the result after pyeloplasty.

In babies, because the kidneys are still maturing, the test is usually done after 6–8 weeks of age.

How is it done?

1. Before the test, the child is given plenty of fluids, sometimes through an IV.
2. The substance is injected into a vein, and the child lies under the camera.
3. A diuretic medicine is injected during the test.
4. At the end, the child sits up or passes urine, and a final image is taken.

The whole test takes about 1 hour. In young children, a catheter is sometimes placed in the bladder.

Preparation

• Drinking plenty of water is very important for an accurate result.
• Fasting is not needed; breastfeed your baby before the test.
• Bring a toy, a tablet and food for your child.