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Galactose-1-phosphate uridyl transferase
Definition:
A test that measures the blood levels of Gal-1-PUT, an enzyme involved in breakdown of milk sugars (lactose/galactose).

Alternative Names:
Galactosemia screen; Gal-1-PUT

How the test is performed:
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill 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 tourniquet 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.

Infant or young child:
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 of paper, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
How to prepare for the test:
Adults:
No special preparation is necessary.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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 in the diet is in the metabolism of lactose. The major source of lactose in the diet is in milk (or 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 is born with a deficiency of Gal-1-PUT (deficiencies of the other enzymes are much less common). As a consequence, galactose accumulates in the blood (that is, 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, hepatomegaly (liver enlargement), cirrhosis, and mental retardation.
Normal Values:
The normal range is 18.5 to 28.5 U/g Hb.

Note: U/g Hb = units per gram of hemoglobin
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.
Review Date: 11/12/2001
Reviewed By: David G. Brooks, M.D., Ph.D., Division of Medical Genetics, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
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