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Understanding Cystic Fibrosis: Diagnosis and Testing Methods

William Wadzinski | MD

Medically reviewed by William Wadzinski | MD, Uniformed Services University of the Health Sciences on July 19th, 2023.

Key Takeaways

  • Newborn screening catches 95% of cases through blood tests measuring immunoreactive trypsinogen (IRT) levels, followed by genetic testing if elevated.
  • The sweat chloride test remains the gold standard for diagnosis—chloride levels above 60 mmol/L confirm the condition, while 30-59 mmol/L suggests possible CF.
  • Genetic testing identifies mutations in the CFTR gene, with F508del being the most common mutation found in 70% of patients worldwide.
  • Pulmonary function tests show characteristic patterns of airway obstruction, with FEV1 (forced expiratory volume) declining an average of 1-2% per year without proper treatment.
  • Comprehensive testing includes pancreatic function assessment through fecal elastase levels—readings below 200 mcg/g indicate pancreatic insufficiency requiring enzyme replacement.

Cystic fibrosis (CF) is a genetic disease that affects the lungs, pancreas, and other organs. If you or a loved one is suspected of having CF, doctors may use various tests to confirm the diagnosis. These tests include blood tests, sweat tests, and sometimes stool tests, along with a review of your symptoms by a specialist.

Newborn Screening for Cystic Fibrosis

All 50 states and the District of Columbia screen newborns for cystic fibrosis. This is usually done with a blood test 24 hours after birth or before the baby and mother leave the hospital. The test measures the level of a chemical called immunoreactive trypsinogen (IRT) in the baby's blood. If the IRT level is high, it indicates an increased risk of CF, and further testing is needed to confirm the diagnosis.

Sweat Chloride Test: The Most Reliable Method

The sweat chloride test is considered the most reliable way to diagnose cystic fibrosis. This test measures the amount of salt (chloride) in a person's sweat. People with CF have higher levels of chloride in their sweat compared to those without the condition. The test can be performed on individuals of any age, but some babies may need to be tested more than once if they do not produce enough sweat.

Understanding Cystic Fibrosis: Diagnosis and Testing Methods

How the Sweat Chloride Test Works

  1. A doctor rubs a small area of the skin on the arm with a special gel that stimulates the sweat glands.

  2. A weak electrical current is used to push the gel into the skin, causing a tingling or warm sensation.

  3. Sweat is collected for 30 minutes in a special device attached to the arm.

  4. The sweat sample is sent to a lab for analysis.

High levels of chloride in the sweat confirm the diagnosis of cystic fibrosis.

Carrier Testing and Prenatal Diagnosis

Cystic fibrosis is caused by a faulty gene inherited from both parents. Individuals can carry this gene without displaying symptoms. If both parents are carriers, there is a risk that their child will be born with CF. Carrier testing involves analyzing DNA from a blood sample or cheek swab to determine if a person carries the faulty gene.

Prenatal testing is available for pregnant women and their partners if both are found to be carriers. This can be done through amniocentesis (checking the amniotic fluid) between the 15th and 20th week of pregnancy or chorionic villus sampling (CVS) between the 10th and 12th week, which involves testing a sample of placental tissue.

Testing for Adults

If an adult is suspected of having cystic fibrosis and was not tested at birth, doctors may recommend both a genetic test and a sweat test. Symptoms that may prompt testing include repeated bouts of pancreatitis, nasal polyps, frequent sinus and lung infections, and infertility.

If you suspect that you or a loved one may have cystic fibrosis, it is essential to consult with a healthcare provider who specializes in this genetic disease. Early diagnosis and treatment can significantly improve the quality of life for individuals with CF.

For more information on cystic fibrosis and its diagnosis, visit:

The Bottom Line

Early diagnosis through newborn screening and confirmatory sweat testing is crucial for starting life-extending treatments before irreversible lung damage occurs. Most diagnoses are confirmed by age 2, though milder cases may not be detected until adulthood. If you're concerned about persistent respiratory or digestive symptoms that could indicate CF, Doctronic can help connect you with appropriate testing and specialist care.

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