Sweat test for cystic fibrosis

Overview

The sweat test is a simple, painless test used to help diagnose cystic fibrosis. Cystic fibrosis is an inherited condition that affects the lungs and digestive system, causing thick, sticky mucus to build up. The sweat test measures the amount of salt (chloride) in a person's sweat. People with cystic fibrosis have higher levels of salt in their sweat.

Cystic fibrosis is not common. It affects about 1 in every 2,500 babies born in the UK. The sweat test is a routine test for babies who may have signs of the condition.

The sweat test is used for anyone suspected of having cystic fibrosis. Most often, it is done in newborns as part of a national screening programme, or in children and adults who have symptoms like persistent lung infections or poor growth.

Symptoms

Common symptoms

• Persistent cough with thick mucus
• Frequent lung infections (pneumonia, bronchitis)
• Wheezing or shortness of breath
• Poor weight gain or difficulty growing
• Salty-tasting skin (a classic sign)
• Bulky, greasy stools (poos)

Symptoms in children

• Delayed growth (failure to thrive)
• Frequent chest infections
• Blocked bowel (meconium ileus) in newborns
• Salty sweat on the forehead

Symptoms in older adults

• Symptoms may be milder but still include chronic lung problems and digestive issues
• Male infertility or absent vas deferens
• Older adults with cystic fibrosis are now living longer with improved treatments

Causes

Main causes

• Cystic fibrosis is caused by a change (mutation) in the CFTR gene, which controls salt and water balance in cells.
• It is an inherited condition, so you need to get a faulty gene from both parents.

Risk factors

• Having a family history of cystic fibrosis
• Being of Northern European ancestry (more common in this group)
• Having parents who are carriers of the faulty gene (they do not have the condition)

When to see a doctor

See a doctor urgently if:

• If you or your child has severe breathing problems or chest pain
• If there is coughing up blood
• If there are signs of dehydration or a blocked bowel

Book a routine appointment if:

• If your child is not growing well or has frequent chest infections
• If there is a family history of cystic fibrosis and you are planning a family
• If you notice unusually salty sweat on your skin

Diagnosis

Cystic fibrosis is diagnosed through a combination of newborn screening, the sweat test, and genetic testing. The sweat test is the key diagnostic test.

Tests that may be done

• Sweat test: A small amount of sweat is collected from the arm or leg using a device that makes the skin sweat a little. The sweat is then analysed for chloride level.
• Genetic test: A blood or cheek swab test looks for changes in the CFTR gene to confirm the diagnosis.
• Newborn screening: In the UK, babies are offered a blood spot test (heel prick) shortly after birth to check for several conditions, including cystic fibrosis.

What to expect at your appointment

The sweat test is done in a hospital or clinic. It is painless and takes about an hour. Your skin will be cleaned, and a small device is placed on the arm or leg that produces a mild tingling or warm feeling. Sweat is collected in a small tube and sent to a lab. Results usually come back within a few days. A high chloride level (over 60 mmol/L) suggests cystic fibrosis.

Treatment

There is no cure for cystic fibrosis, but treatments can help manage symptoms, improve quality of life, and extend life expectancy. Treatment is tailored to each person and often involves a team of specialists.

Self-care at home

• Do daily chest physiotherapy to help clear mucus from the lungs
• Stay hydrated and eat a high-calorie, high-fat diet (as recommended by a dietitian)
• Take prescribed enzyme supplements to help digest food
• Avoid smoking and second-hand smoke

Medical treatments

Medical treatment includes medications to thin mucus (mucolytics), antibiotics to fight lung infections, anti-inflammatory drugs, and enzyme replacement therapy to aid digestion. Newer therapies called CFTR modulators can help correct the faulty protein in some people. Treatment plans are managed by a specialist cystic fibrosis team.

When is surgery considered?

Surgery is not common but may be considered for severe cases, such as a lung transplant or surgery to correct a bowel blockage in newborns.

Living with this condition

Living with cystic fibrosis requires a daily routine of treatments, including physiotherapy, taking medications, and monitoring symptoms. Many people with CF lead active lives, go to school or work, and have families. With modern treatments, life expectancy has improved significantly.

Lifestyle tips

• Follow a high-energy diet with plenty of calories and salt
• Exercise regularly to help clear lungs and build strength
• Get vaccinated against flu, pneumonia, and COVID-19
• Avoid contact with people who have colds or infections

Diet and exercise

A dietitian will recommend a diet high in calories, protein, and fat, plus extra salt in hot weather. Pancreatic enzyme supplements help absorb nutrients. Regular exercise, such as swimming or cycling, helps improve lung function and fitness.

Mental health and emotional wellbeing

Living with a chronic condition can be emotionally challenging. It is normal to feel anxious, stressed, or sad at times. Many people find it helpful to talk to a counsellor or psychologist, or connect with others who have CF. It's important to look after your mental health as well as your physical health.

Prevention

Cystic fibrosis cannot be prevented because it is genetic. However, genetic counselling can help families understand the risks and options, such as prenatal testing or preimplantation genetic diagnosis (PGD).

Vaccines

People with cystic fibrosis should have all routine childhood vaccinations, as well as annual flu shots and vaccines for pneumonia and COVID-19. These help prevent infections that could be more severe.

Screening programmes

Newborn screening in the UK includes a blood spot test that can detect cystic fibrosis early. Carrier testing is available for adults with a family history or who are planning a pregnancy.

Complications

If left untreated

• Chronic lung damage and respiratory failure
• Frequent and severe lung infections
• Malnutrition and poor growth
• Diabetes related to cystic fibrosis
• Liver disease
• Infertility in males
• Reduced life expectancy

Long-term outlook

With early diagnosis and modern treatments, many people with cystic fibrosis now live into their 40s, 50s, and beyond. Each person's outlook depends on their specific genetic mutation and how well the condition is managed. A positive, proactive approach to treatment can make a big difference.

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