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Cystic Fibrosis Genetic Carrier Testing

Does this test have other names?

Cystic fibrosis genetic testing

What is this test?

This test is done to see if you carry a defective gene that may cause cystic fibrosis (CF)  in your child. A defect in a gene is called a mutation. Genes are made from DNA, and mutations can be found by doing special tests that look at your DNA.

CF is a serious disease that causes thick mucus to form in the lungs and digestive system. CF may be treated, but the disease has no cure. Most people with this disease only live into their 30s or 40s.

You may have one of the genes that cause CF without having the disease. That's because in order to have the disease, you must have inherited CF genes from both of your parents. Having one of the genes that causes CF, but not having the disease, is called being a carrier. 

Why do I need this test?

The American Congress of Obstetricians and Gynecologists recommends that all couples who are pregnant or thinking of getting pregnant consider carrier testing for CF. You may choose to have this test if:

  • You are considering becoming a parent

  • You or your partner is pregnant

  • You have a family history of CF and you want to know whether you are a carrier of the gene

Your chances of being a carrier of the CF gene are higher if you have a family history of the disease. More than 10 million Americans are carriers of this gene, and many don't know it. Your racial background has a lot to do with your risk for being a carrier. The risk is about:

  • 1 in 29 for Caucasian (white) Americans

  • 1 in 46 for Hispanic Americans

  • 1 in 65 for African-Americans

  • 1 in 90 for Asian Americans

Making the decision to find out whether your child may be born with Cf may be difficult. It's important to discuss this decision with a genetic counselor, your doctor, your partner, family members, and possibly a religious counselor. 

What other tests might I have along with this test?

You may have other tests to screen for diseases or conditions that could be passed on to your child. These types of tests may be included in your prenatal testing. 

What do my test results mean?

A result for a lab test may be affected by many things, including the method the laboratory uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Your doctor or a genetic counselor will discuss your test results with you and help you understand what they mean. If your test result is positive, it says you are a carrier of the CF gene. The result is more than 99 percent accurate.

A negative result is not as accurate. Even if your test result says you are not a carrier, you may still have a slight chance of being a carrier for one of the rare types of gene mutations that do not show up on the test.

If you are a carrier but your partner tested negative for CF, there is still a slight chance that your child will be born with the disease.

It's important to know whether you carry the gene, and you may want to let other family members know if the gene runs in your family. If you and your partner are both carriers, this is what your tests may mean:

  • Your child has a 50 percent chance of being a carrier of the CF gene but will not have the disease.

  • Your child has a 25 percent chance of having CF.

  • Your child has a 25 percent chance of not having CF or being a carrier. 

How is this test done?

The test requires cells from your body so that your DNA can be studied. This may be done with a blood sample, which is drawn by putting a needle into a vein in your arm. You may also have a swab rubbed inside your mouth to get cells from inside your cheek.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore. A cheek swab does not carry any significant risks.  

What might affect my test results?

No medications or conditions will affect your test results.

How do I get ready for this test?

You don't need to prepare for this test.