How is cystic fibrosis diagnosed?

Most babies in New Zealand are tested for CF through the Newborn Metabolic Screening Programme, often referred to as the Guthrie Heel Prick test. This test, usually carried out about 48 hours after birth, uses a blood sample taken from a baby’s heel and screens it for rare disorders, such as CF.

Tailen CF 2018 with Mickey

If this test shows the baby has a high level of an enzyme called immunoreactive trypsinogen (IRT), which is elevated in most babies with CF, a second test is done using the same heel prick sample to look for common mutations of the CF gene in New Zealand. This is called a positive screen, meaning the baby is either a carrier (has one CF gene) or has CF (has two CF genes).

The lead maternity carer is notified of the results and will refer the baby to a local paediatrician who will organise further tests and an appointment to see the baby.

Further tests to confirm your baby’s diagnosis are:

Sweat test

A sweat test measures the amount of salt (sodium and chloride) in the baby’s sweat and is usually done when they weigh over 3kg. An abnormally high chloride result indicates CF. Occasionally, results are inconclusive, or not enough sweat is collected, so the test needs to be repeated when the baby is older.

Stool (poo) test

The baby’s poo will be tested for an enzyme called elastase – a low level is common in babies with CF.

Blood test

The baby will have another blood test to ensure a correct diagnosis and to identify their CF gene mutation.

Usually a local paediatrician will review all the test results and confirm their diagnosis of CF.

Other factors

For a small number of babies, the first symptom of CF is a blocked intestine at birth, called meconium ileus. Meconium is the normal black sticky secretion from a baby’s bowel, usually passed in the first 24 hours after birth. In some babies with CF, the meconium is too thick to pass and blocks the intestine, needing enemas or surgery to remove it.

Occasionally, other factors such as siblings with CF or early symptoms such as breathing difficulties, malabsorption or poor weight gain may have led your baby to be tested for CF.

Children born in a country without newborn screening may not be diagnosed until they are older.


Find out more about the genetics of cystic fibrosis

Late diagnosis

Occasionally, CF is diagnosed in adolescence or adulthood, known as a late diagnosis.

If you’ve been diagnosed later in life, it may mean you have a milder form of CF or your symptoms are atypical (not the usual symptoms). Often the diagnosis is made during investigations for other health issues such as recurrent bronchitis, atypical asthma or allergies, fertility issues, colitis, gastro-intestinal problems or a sudden respiratory illness.

Following diagnosis you will be referred to a specialist multidisciplinary team, including doctors, nurses, physiotherapists, psychologist and dietitians, who will work with you to develop a treatment plan. Often this includes daily medications, physiotherapy and nutritional support. Regular exercise is also strongly encouraged.

Receiving a late diagnosis may come as a relief if you have been struggling with ongoing health concerns, but it also impacts your lifestyle and how you manage your health moving forward. Adjusting to the many changes required to manage CF can be challenging, but your healthcare team will help you develop routines to suit your lifestyle.

If you're concerned you may have cystic fibrosis, please contact your GP.

Receiving a diagnosis

If you've received a diagnosis of cystic fibrosis you will be introduced to the medical and nursing team who will care for your child. You will also be referred to Cystic Fibrosis New Zealand for support from our field workers and other support services.

Find out more about a new diagnosis