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
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
- 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.
The test for
Tay-Sachs disease measures the amount of an
enzyme called hexosaminidase A (hex A) in the
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.
person who has about half the normal amount of hex A is a
- 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
- 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.