Galactosemia Test

Explains test for galactosemia, a rare disease passed from parents to children. Covers blood or urine test that checks a newborn for enzymes needed to change galactose from milk into glucose, a sugar used for energy. Explains why and how the test is done.

Galactosemia Test

Test Overview

Galactose is a sugar that is part of the lactose found in milk and milk products. A galactosemia test is a blood or urine test that checks for enzymes that are needed to change galactose into glucose, a sugar that your body uses for energy. A person with galactosemia doesn’t have one of these enzymes, so high levels of galactose build up in the blood or urine.

When galactose builds up in a baby’s blood, it can cause liver damage, problems with eating, and intellectual disabilities. The damage caused by galactosemia can begin within weeks after the baby has started drinking breast milk or formula. Babies with galactosemia need foods low in galactose in order to gain weight and to prevent brain damage, liver problems, infection, and cataracts.

Galactosemia is a rare disease that is passed from parents to children (inherited genetic disorder). A galactosemia test is usually done to determine whether a newborn has the disease. In a family with a member who has galactosemia, a genetic test can be done on adults to find out whether they have an increased chance of having a child with the disease.

Why It Is Done

A galactosemia test is done to:

  • Find out whether a newborn has the enzymes needed to change galactose into glucose.
  • See whether diet changes are working for a child who has galactosemia.

How To Prepare

You do not need to do anything before you have this test.

Talk to your doctor about any concerns you have about the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form( What is a PDF document? ).

How It Is Done

Tests for galactosemia are done on a blood or urine sample.

Blood sample from a heel stick

If galactosemia testing is done on a baby, a heel stick will be done instead of a blood draw from a vein. For a heel stick blood sample, several drops of blood are collected from the heel of the baby. The skin of the heel is cleaned with alcohol and then punctured with a sterile lancet. Several drops of blood are collected inside circles on a specially prepared piece of paper. When enough blood has been collected, a gauze pad or cotton ball is placed over the puncture site. Pressure is maintained on the puncture site briefly to stop the bleeding, and then a small bandage is usually applied. A blood sample is usually collected within 2 to 3 days after birth.

If the test shows that the baby has galactosemia, the results will be confirmed on a blood sample taken from a vein.

Blood sample from a vein

The health professional drawing your child’s blood will:

  • Wrap an elastic band around your child’s upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
  • Clean the needle site with alcohol.
  • Put the needle into the vein. More than one needle stick may be needed.
  • Attach a tube to the needle to fill it with blood.
  • Remove the band from your child’s arm when enough blood is collected.
  • Apply a gauze pad or cotton ball over the needle site as the needle is removed.
  • Apply pressure to the site and then a bandage.

Urine sample

To test for galactose in a urine sample from a baby, a health professional will tape a plastic collection bag to the baby’s genital area. After the baby urinates, the collection bag is removed. A blood test for galactose is more accurate than a urine test.

How It Feels

Blood sample from a heel stick

A quick sting or a pinch is usually felt when the lancet punctures the skin. Your baby may have a little discomfort with the skin puncture, but this does not last long.

Blood sample from a vein

Your baby may feel nothing at all from the needle puncture, or he or she may feel a brief sting or pinch as the needle goes through the skin. Some people feel a stinging pain while the needle is in the vein. But many people do not feel any pain (or have only minor discomfort) after the needle is positioned in the vein. The amount of pain you feel depends on the skill of the health professional drawing the blood, the condition of your baby’s veins, and your baby’s sensitivity to pain.

Urine sample

A baby will usually feel no discomfort from the use of a urine collection bag. But removing the tape that attaches the bag to the skin may cause temporary discomfort.


Heel stick blood sample

There is very little risk of a problem from a heel stick. Your baby may get a small bruise at the puncture site.

Blood sample from a vein

There is very little chance of a problem from having blood drawn from a vein.

  • Your baby may get a small bruise at the puncture site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
  • In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. You can use a warm compress several times a day to treat this.

Urine sample

There are no risks linked with a urine test for galactosemia. Removing the tape that holds the bag in place may cause mild skin irritation.


A galactosemia test is a blood or urine test that checks for the enzymes that are needed to change galactose into glucose, a sugar that your body uses for energy.

Galactose tests (blood or urine)


Negative (galactosemia is not present)


Positive (galactosemia is present)

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what’s normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Galactose-1-phosphate uridyltransferase (GPT) test (blood)

Normal:footnote 1

18.5–28.5 units per gram (U/g) of hemoglobin (1.19–1.84 milliunits per mole of hemoglobin [mU/mol Hb]): The person does not have galactosemia.

Abnormal:footnote 2

Less than 5 U/g of hemoglobin (less than 0.32 mU/mol Hb): The person has galactosemia.

5–18.5 U/g of hemoglobin (0.32–1.18 mU/mol Hb): The person may be a carrier of galactosemia and able to pass the disease on to his or her child.

Galactokinase enzyme test (blood)footnote 1


Adults: 12–40 milliunits per gram of hemoglobin (mU/g Hb) (200–667 pkat/g Hb)

Children 2–18 years: 11–54 mU/g Hb (183–900 pkat/g Hb)

Children 0–2 years: 11–150 mU/ g Hb (183–2500 pkat/g Hb)


Lower-than-normal values, depending on age

A newborn screening test that shows the baby has an increased risk of galactosemia will be confirmed by other tests.

Many conditions can change galactose levels. Your doctor will discuss any significant abnormal results with you in relation to your baby’s symptoms and past health.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • A blood transfusion.
  • Improper placement of a urine collection bag on a baby.

What To Think About

  • Early detection and treatment of galactosemia is very important, because the disease can cause brain damage, liver failure, and cataracts if it is not treated. Within 24 hours of drinking breast milk or formula, galactose blood levels in a baby with galactosemia start to rise. A galactosemia test 2 to 3 days after birth will show whether your baby has galactosemia. Almost all states in the United States have laws that require galactosemia testing of newborns within a few days of birth.
  • If your baby’s test is positive, the test will be repeated to confirm the diagnosis.
  • If test results confirm that your baby has galactosemia, ask to speak to a dietitian. A substitute for breast milk or milk-based formula, such as formula made from soy, will prevent damage caused by galactosemia. It will never be safe to give milk or milk products to a child who has galactosemia.
  • If you or your partner knows that you are a carrier of galactosemia or if you have family members with galactosemia, you may want to have genetic counseling to learn about the disease and the likelihood of passing it to your children. To learn more, see the topic Genetic Test.



  1. Fischbach F, Dunning MB III (2015). A Manual of Laboratory and Diagnostic Tests, 9th ed. Philadelphia: Wolters Kluwer Health.
  2. Chernecky CC, Berger BJ (2013). Laboratory Tests and Diagnostic Procedures, 6th ed. St. Louis: Saunders.

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.


Current as ofApril 1, 2019

Author: Healthwise Staff
Medical Review: Kathleen Romito, MD – Family Medicine
Martin J. Gabica, MD – Family Medicine
Adam Husney, MD – Family Medicine
Siobhan M. Dolan, MD, MPH – Reproductive Genetics

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