Making the diagnosis of cystic fibrosis (CF) is paramount so that early education and treatment strategies can be put in place to maximise health outcomes. In most cases, CF is diagnosed through the newborn screening test, also known as the Guthrie test.
Some babies are born with meconium ileus, which may be an earlier sign of CF. It occurs in approximately 20% of patients with CF.
Newborn Screening Test
The newborn screening test is a simple heel prick test that is routinely done on all newborn babies in Australia. The test screens for a range of serious disorders and is usually performed when the baby is between 2-3 days old. Testing for CF was added to the newborn screening test in Western Australia in 2000. It is provided free of charge.
The newborn screening test for CF is based on a widely adopted two-stage protocol that involves the measurement of ImmunoReactive Trypsinogen (IRT) levels and DNA testing.
IRT, which is produced by the pancreas, is a chemical in the blood that is normally found in small levels in the body. If the IRT level is high, this may indicate that the baby has CF, however, levels can also be high if a baby is premature, has had a stressful delivery or for other reasons.
Following a raised IRT, another test is required to determine if the child has CF. This is done by testing the DNA for the common CF gene mutations. If the newborn has two CF gene mutations, they are diagnosed with CF; if only one mutation is found, a sweat test is ordered, and if no mutations are found, no further testing is required.
Aims of Newborn Screening for CF
The aim of newborn screening for CF is to optimise health by early diagnosis and management. Early management and treatment is associated with improved outcomes and access to new treatments as they become available.
Early diagnosis also offers parents awareness of their carrier status prior to future pregnancies.
How Reliable is the CF Screening Test?
Newborn screening for CF detects approximately 95% of all infants born with CF. The screening program is assisted when notified if a child is clinically suspected of having CF or where there is a family history of CF.
Infants who are found to have two of the common CF gene mutations are referred to a paediatrician who specialises in caring for children with CF. In WA, this will be the CF Clinic at Perth Children’s Hospital (PCH). Here, a sweat test will be performed to confirm the diagnosis of CF.
Infants who carry only one of the common CF gene mutations will have a sweat test at 4-6 weeks of age. Most of these infants will have a normal sweat test result. These are healthy infants who are carriers of a CF gene. However, about 1 in 6 will have a positive sweat test result and be diagnosed with CF. They carry one of the common gene mutations plus an unidentified CF gene mutation.
The sweat test measures the amount of chloride in the sweat. There are no needles involved and it takes about an hour. For a child who has CF, the sweat test results will be positive, showing a high chloride level.
For infants up to and including 6 months of age, a chloride level:
- Equal to or less than 29 mmol/L: NEGATIVE – means CF is highly unlikely
- Between 30 – 59 mmol/L: INTERMEDIATE – means CF is possible
- Greater than or equal to 60mmol/L: POSITIVE – means CF is likely to be diagnosed
For a small number of infants with sweat test results falling into a borderline range, described as intermediate, a repeat sweat test is usually done to confirm or rule out diagnosis of CF.
While most new CF diagnoses are detected through newborn screening, a small percentage of people are identified later in life. Adult diagnosis, also known as late diagnosis, is defined as an individual, 18 years and over, who is found to have CF.
Most adult diagnoses are made when an individual experiences ongoing symptoms. Common symptoms are coughing, recurrent chest or sinus infections, infertility, failure to gain weight and for some, abnormal bowel movements. For these people, the key diagnostic tool is a sweat test.
A late diagnosis of CF often brings a sense of relief to people as they finally have an answer to why they have been unwell for so long. It also means that they now have access to the best possible treatment and support. On the other hand, a late diagnosis can be a shock and many individuals experience confusion and can feel overwhelmed.
An important first step is to learn about the new condition and what is required to manage the symptoms. You can see the About CF page for more information.
The CF hospital team and CFWA are available for support and understand that it takes time to comprehend and accept the diagnosis of CF.
Cystic Fibrosis WA Support
CFWA offer a range of support and services to individuals and families affected by CF.
If your baby has been diagnosed with CF, more information can be found on our Living with CF – Newborn page.
If you are a late diagnosis, you can find more support on our Living with CF- Adult page.