Cystic Fibrosis Carrier Testing

About 30,000 Americans have cystic fibrosis (CF), a genetic disorder that primarily affects the lungs and digestive system.

CF is caused by genetic defects in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. People with CF carry two defective copies of the CFTR gene, one from each parent.

People who carry only one defective CFTR gene do not have CF but are CF carriers. If they have a baby with another CF carrier, they have a 1 in 4 chance of having a child with CF.

Who's Most At-Risk for Cystic Fibrosis?

Verywell / Jessica Olah

10 Million Americans Are CF Carriers

Cystic fibrosis is most common among people of European descent. It affects 1 in 3,500 live births of European Americans in the United States, but only 1 in 17,000 live births among African Americans, 1 in 4,000 to 1 in 10,000 live births among Hispanics, and 1 in 31,000 live births among Asian Americans.

Although CF is rare, being a CF carrier is relatively common. In the United States, 1 out of every 31 people is a CF carrier. As with CF, the carrier rate is highest among people of European descent and lower among people of other ethnic groups.

If no one in your family has CF, your chance of being a carrier depends on your ethnic background, such as:

  • European Caucasians, Ashkenazi Jews: 1 in 29
  • Hispanic Americans: 1 in 46
  • African Americans: 1 in 61
  • Asian Americans: 1 in 90

Carrier Status: Genetic Testing

Genetic testing can tell you if you are a CF carrier. Genetic tests look at your DNA (genetic material). Your DNA is extracted either from a blood sample or from a swab of the cells inside your mouth and analyzed for common CF-causing mutations.

The standard genetic test for CF looks for the 23 most common CF-causing mutations in the CFTR gene. The exact mutations screened for in the test will depend on your ethnic background and family history. If you have a relative with CF or who is a known carrier, you have a greater chance of also being a carrier.

Who Should Get Tested?

Because being a CF carrier does not typically cause symptoms, most people are unaware they are carriers unless they are tested.

Getting tested for CF is a personal choice. The American College of Obstetricians and Gynecologists (ACOG) recommends physicians offer prenatal genetic screening for CF and other genetic conditions to anyone planning to become pregnant or are already pregnant. People with Ashkenazi Jewish or European ancestry have the highest chances of being a carrier.

If you or your partner test negative, your baby cannot develop CF, and the other person does not need testing.

If you have a child with CF, all the child's siblings should be tested for CF, regardless of whether they have symptoms. Your other relatives may also wish to be screened to see if they carry a CF-causing mutation.

Interpreting Your Test Results

If your screening test comes back positive, you have an over 99% chance of carrying a defective CFTR gene.

If your test comes back negative, you do not carry one of the common mutations that lead to CF. It is still possible, although unlikely, that you carry a rare mutation not screened for. Research has identified over 1,700 different mutations that can cause CF—but most of these mutations are extremely rare.

Testing for these rare mutations may be warranted if your partner has a CF-causing mutation, or if you have a family member who is a CF carrier. Be sure your doctor is aware of your family history and any concerns you might have.

Children of Carriers May Be at Risk

CF is an autosomal recessive genetic disorder, meaning that to develop CF a person must inherit a defective CFTR gene from each parent. Only two carriers can have a baby with CF.

If a CF carrier has a baby with another CF carrier, that baby has:

  • a 25% chance of not being a carrier
  • a 50% chance of being a carrier
  • a 25% chance of having CF

If a CF carrier has a baby with someone who is not a carrier, the baby has a 50% chance of being a CF carrier and a 0% chance of having CF.

If a carrier has a baby with someone who has CF, that baby has a 50% chance of having CF and a 50% chance of only being a carrier.

Cystic Fibrosis Testing During Pregnancy

If you are pregnant and you and your partner both test positive for a CFTR mutation, or if you are positive and your partner's carrier status is unknown, you can have your baby tested for cystic fibrosis during pregnancy. These tests are performed via chorionic villus sampling or amniocentesis in the first half of pregnancy.

These tests involve taking and extracting DNA from a small sample of the baby's placenta or the pregnant parent's amniotic fluid. The DNA is then analyzed for common genetic disorders, including CF.

If you decline prenatal screening, your baby will be screened at birth. All newborns in the United States are now screened for CF shortly after birth. This is done with a blood sample collected via a heel stick.

A positive result is then confirmed or ruled out using a sweat chloride test—a test that looks at the amount of chloride in your baby's sweat. If your baby tests positive, genetic testing is recommended to determine your baby's specific mutations, which will help guide proper treatment.

Higher Likelihood of CF-Related Health Conditions

Because CF carriers have one functioning copy of the CFTR gene, they do not have cystic fibrosis, and generally do not experience any symptoms of the disease.

Recent research, however, has found that CF carriers do face certain elevated health risks compared to noncarriers. These health risks are a milder form of those seen in people with CF, and include:

  • Reduced fertility in women
  • Male infertility
  • Pancreatitis (inflammation of the pancreas)
  • Bronchiectasis (widening of the airways leading to mucus buildup)
  • Certain types of lung infections
  • Sinusitis (inflammation of the spaces in the nose and head)
  • Diabetes (high blood sugar levels)
  • Arthritis (swelling and pain in joints)
  • Constipation (difficulty moving bowels)
  • Dehydration (loss of fluid from the body) during exercise
  • Scoliosis (sideways curvature of the spine)

Notably, these health risks and associated symptoms are quite mild compared with CF—a chronic condition that requires hours of daily management and significantly shortens the lifespan. For example, a person with CF needs nutritional supplements from birth due to pancreatic insufficiency, whereas a CF carrier has a slightly elevated, but still less than one in a hundred, risk of developing pancreatitis. Most CF carriers will not experience any of these health problems.

A Word From Verywell

Being a cystic fibrosis carrier is very common. It is not typically linked with any symptoms or health problems, although being a carrier can slightly raise your risk of certain conditions, like male infertility and pancreatitis (inflammation of the pancreas). Talk with your healthcare provider if you have concerns about how being a CF carrier is impacting your health.

Aside from certain slightly elevated health risks, the main concern with being a carrier is the potential to have a child with cystic fibrosis if you conceive a child with someone who is also a carrier. If you are planning to become pregnant, your healthcare provider should offer carrier testing for you and your partner. Certain types of prenatal screening, such as amniocentesis, can also detect cystic fibrosis before your baby is born.

Frequently Asked Questions

  • How serious is cystic fibrosis?

    Cystic fibrosis is a serious, life-threatening disorder that primarily affects the lungs and the pancreas. It causes chronic lung infections and a progressive decline in lung function that shortens the lifespan. Advances in treatment have greatly improved survival of people with CF. Only a few decades ago, most died in childhood. Today, babies born with CF can expect to live into their 40s and 50s.

  • How does cystic fibrosis affect fertility?

    Nearly all men with CF (97%–98%) are born with a condition known as congenital bilateral absence of the vas deferens (CBAVD). They lack the canals through which the sperm pass into the semen and, therefore, cannot fertilize an egg via intercourse. Because these men do produce sperm, they can often have biological children with assisted reproductive procedures involving sperm extraction. Women with CF are fertile, but they may have reduced fertility because of thicker than normal cervical mucus and ovulation issues related to poor nutrition.

  • Does being a cystic fibrosis carrier affect fertility?

    Women who are carriers have normal fertility. Men who are carriers may occasionally have reduced sperm quality or have the same congenital defect seen in men with CF: congenital bilateral absence of the vas deferens (absence of the sperm canals). For men with this congenital defect, because their semen does not contain sperm, they cannot conceive via intercourse. But because they do produce sperm, they can often have children with assisted reproductive techniques.

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11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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