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Cystic Fibrosis Testing

In the 1990s, a genetic test was developed that could identify people who carry the mutation associated with cystic fibrosis, a genetic disorder affecting the respiratory, digestive and reproductive systems. Several genetic and health professional organizations have issued recommendations on when it is appropriate to use the test. This page provides background about the disease and information on some of the testing recommendations.

What is cystic fibrosis?
About 30,000 American children and young adults are living with cystic fibrosis. The disease attacks the lungs, clogging them with a thick mucus, and it can harm digestion and vitamin absorption by clogging the pancreas and intestines as well. While treatment has improved in recent years, patients typically die in their 30s, most from lung damage or infection. While it can affect anybody, cystic fibrosis is the most common inherited disease among Caucasians and affects this group more frequently than any other ethnic group.

What role does genetic testing play?
Cystic fibrosis is an autosomal recessive disorder, which means a copy of a mutated gene must be inherited from each parent in order for a baby to be born affected with the disease.

People can carry the defective gene without knowing it - more than ten million Americans do, including one in every 29 whites (which translates into about one in every 3500 Caucasian babies born affected with CF). Because there are so many unsuspecting carriers, most babies with the disease are born into families that did not know they were at risk. If both parents harbor the defective gene, they have a one-in-four chance of having a baby with CF.

When should testing be performed?
Testing is best performed prior to a woman getting pregnant. If both parents are determined to be carriers, they may opt for in vitro fertilization, where the resulting embryos can be tested for the disease and only healthy ones are implanted into the mother's uterus.

If parents learn they are carriers during pregnancy, the fetus can be tested. If the fetus does have it, terminating the pregnancy is one option, but many parents do not end their pregnancies because their fetus has CF. They elect to continue and spend the remaining months of pregnancy learning about different care available for a child with CF. Very early care, especially nutritional care, increases the chances for a healthy infanthood.

A test typically costs about $265 (as of 2001), and physicians say many insurers will cover it. Every patient should check with their health insurance carrier prior to testing to determine whether they will be responsible for payment.

How accurate is the test?
The test is good but not 100 percent accurate. There are about 1,000 known mutations in the cystic fibrosis causing gene, and the new guidelines advise test laboratories to check for a minimum of the 25 most common mutations. Genzyme Corporation, the largest test provider, typically tests for 87 mutations, which rules out greater than 90% of Caucasian mutations. How well this widespread gene testing works will influence how other gene tests are introduced to Americans.