Hexosaminidase Test-Why am I having this test?

Hexosaminidase test is done to determine if someone has Tay–Sachs or Sandhoff disease or is a carrier of the disease. This test may be done in a child to confirm a diagnosis of Tay–Sachs or Sandhoff disease.

For people who are thinking about becoming parents, the test is usually done on both the mother and the father to determine if they are carriers of the gene that causes the disease.

You may need to meet with a genetic counselor prior to having this test. Additional genetic testing may be done.

What is being tested?

This test measures the amount of the hexosaminidase A (hex A) enzyme in the blood. This test also measures the total hexosaminidase, which is the amount of hex A and another enzyme, hex B, in the blood.

What kind of sample is taken?

A blood sample is required for this test. How it is collected usually depends on the age of the person being tested:

• Adult: Collected by inserting a needle into a blood vessel.
• Infant: Collected by pricking the baby’s heel (heel stick).
• Newborn: Collected from the umbilical cord.

Pregnant women can also be tested by using a sample of amniotic fluid (amniocentesis) or a sample of tissue from the placenta (chorionic villus biopsy).

How are the results reported?

The test results will be reported as values. A health care provider will compare the results to normal ranges that were established after testing a large group of people (reference ranges). Reference ranges may vary among labs and hospitals. For this test, common reference ranges are:

• Hexosaminidase A: 7.5–9.8 units/L (SI units).
• Total hexosaminidase: 9.9–15.9 units/L (SI units).

What do the results mean?

Decreased levels of hex A may indicate that you are a carrier of the disease, or that your child has Tay–Sachs disease.

Decreased levels of total hexosaminidase may indicate that your child has a rare type of Tay–Sachs disease called Sandhoff disease.

Talk with your health care provider about what the results mean.

Questions to ask your health care provider

Ask your health care provider, or the department that is doing the test:

• When will the results be ready?
• How will I get the results?
• What are the treatment options?
• What other tests do I need?
• What are my next steps?

Summary

• The hexosaminidase test is done to determine if someone has Tay–Sachs or Sandhoff disease or is a carrier of the disease. This test may be done in a child to confirm a diagnosis of Tay–Sachs or Sandhoff disease.
• The test measures the levels of the hexosaminidase A enzyme and total hexosaminidase in the blood. Lower-than-normal levels may indicate that you are a carrier or that your child has Tay–Sachs disease.
• Talk with your health care provider about what the results mean.