Galactose-1-phosphate uridyltransferase

Definition

Galactose-1-phosphate uridyltransferase is a blood test that measures the level of GALT, an enzyme involved in breakdown of milk sugars (lactose/galactose).

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 puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. 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:

The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.

How to prepare for the test

No special preparation is necessary.

How the test will feel

When the skin is pricked with the needle, the amount of discomfort varies. Some people experience moderate pain while others feel only a prick or stinging sensation. Afterward, the site may be bruised for a few days.

Why the test is performed

This is a screening test for galactosemia.

In normal diets, the major source of galactose is in the metabolism of lactose. The major source of dietary lactose is milk and dairy products. In most people, galactose is converted to glucose by a series of chemical reactions. Each chemical reaction is catalyzed by an enzyme.

About 1 out of 65,000 newborns has a deficiency of the GALT enzyme (deficiencies of the other enzymes are much less common). As a consequence, galactose accumulates in the blood (galactosemia) and tissues because it cannot be metabolized.

Because milk is an important part of the diet of most newborns, these infants develop fluid imbalance and failure to thrive. Continued use of galactose can also result in cataracts, jaundice, liver enlargement, cirrhosis, and mental retardation.

Normal Values

The normal range is 18.5 to 28.5 U/g Hb (units per gram of hemoglobin).

It is important to note that normal values vary from laboratory to laboratory.

What abnormal results mean

• Galactosemia is indicated by a significantly reduced level of activity.
• Further tests should be done to confirm the diagnosis of galactosemia.
• A specialist in biochemical genetics should be consulted promptly.
• The child should immediately be placed on a no-milk diet (no breast milk, no animal milk).

What the risks are

Risks are associated with venipuncture:

• Multiple needle sticks may be performed if the first one 'misses' a vein
• Excessive bleeding
• Hematoma (blood collection under the skin)
• Infection (a risk any time the skin is broken)

Special considerations

Although the disease can be treated by removing milk from the diet, early recognition is essential. Some states, in fact, require that all newborns be screened for this disorder. These screening tests are set to be very sensitive so as not to miss many infants with galactosemia. Therefore, screening tests will come back abnormal but follow-up testing to confirm the abnormal result show the baby to be normal in many cases.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Page Content:

Galactosemia screen; GALT; Gal-1-PUT