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Tay-Sachs Test

How It Feels

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Risks

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

  • You may get a small bruise at the 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. A warm compress can be used several times a day to treat this.
  • Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Results

The test for Tay-Sachs disease measures the amount of an enzyme called hexosaminidase A (hex A) in the blood.

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.

 

Enzyme measured

Normal value1

Amount in blood:

Total hexosaminidase (A+B)

9.8–15.9 units per liter (U/L)

Amount in blood:

Hexosaminidase A

7.2–9.8 units per liter (U/L)

  • A person who has about half the normal amount of hex A is a Tay-Sachs carrier.
  • A person who does not have any hex A has Tay-Sachs disease.
  • In rare cases, a person may not have either hex A or hex B enzyme. This causes a more severe condition called Sandhoff's disease.

What Affects the Test

If you had a recent blood transfusion, you may not be able to have the test, or the test results may not be helpful. If you have a blood transfusion from a blood donor who has normal levels of hexosaminidase A, your level may temporarily be higher than usual.

What To Think About

  • A positive Tay-Sachs test may need to be confirmed with other genetic tests. For more information, see the topic Genetic Test.
  • People who have a high chance of being a carrier of Tay-Sachs may want to have a blood test to see whether they are carriers before they have children. People of Ashkenazi Jewish, French-Canadian, or Cajun descent who have a family history of Tay-Sachs disease or who live in a community or population with a high amount of Tay-Sachs disease may want to be tested. Genetic counseling is available for people who have the disease or are carriers.

WebMD Medical Reference from Healthwise

Last Updated: September 06, 2011
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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