The test for Tay-Sachs disease measures the amount of an enzyme called hexosaminidase A (hex A) in the blood. Hex A breaks down fatty substances in the brain and nerves. Tay-Sachs is an inherited disease in which the body can't break down fatty substances as it should, so the fatty substances collect in the body and damage brain and nerve cells.
Tay-Sachs can occur when parents pass on a changed gene to their child.
A Tay-Sachs test may also measure the amount of another enzyme, called hexosaminidase B. People who cannot make either hex A or B have a rare, more serious condition called Sandhoff's disease.
The Tay-Sachs test is usually done on blood taken from a vein or from the umbilical cord right after birth. It can also be done on a sample of amniotic fluid (collected during amniocentesis) or on cells from the placenta (collected during chorionic villus sampling).
Why It Is Done
A test to measure hexosaminidase A is done to:
How To Prepare
You do not need to do anything before having this test. If you are having this test to see whether you are a Tay-Sachs carrier, you should tell your doctor if you have had a blood transfusion in the past 3 months.
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 may 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
The health professional taking a sample of your blood will:
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.
There is very little chance of a problem from having a blood sample taken from a vein.
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.
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
eMedicineHealth Medical Reference from Healthwise
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