Definition of Galactose-1-phosphate uridyltransferase:

Galactose-1-phosphate uridyltransferase is a blood test that measures the level of a substance called GALT, which helps break down milk sugars (lactose/galactose). Low levels of this substance cause a condition called galactosemia.

How the test is performed:

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

How to prepare for the test:

For help preparing your baby for the test, see infant test or procedure preparation (birth to 1 year).

How the test will feel:

When the needle is inserted to draw blood, some infants feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed:

This is a screening test for galactosemia.

In normal diets, most galactose comes from the breakdown (metabolism) of lactose, which is found in milk and dairy products. About 1 out of 65,000 newborns lack a substance (enzyme) called GALT. Without this substance, the body can't break down galactose, and the substance builds up in the blood. Continued use of milk products can lead to:

• Cataracts
• Cirrhosis
• Failure to thrive
• Jaundice
• Liver enlargement
• Mental retardation

This can be a serious condition if not treated.