Newborn screening, also known as the heel prick test, is offered to babies at five days old to test for several serious but rare conditions, including cystic fibrosis (CF). For some babies, a positive newborn screening result suggests that they might have CF, but follow-up tests do not confirm a diagnosis of CF. This is called ‘Cystic Fibrosis Screen Positive, Inconclusive Diagnosis’ (CFSPID).
What is cystic fibrosis?
Cystic fibrosis (CF) is an inherited condition that causes a build-up of thick sticky mucus in the lungs, digestive system, and other organs. This mucus causes a range of symptoms affecting the entire body. Most children are diagnosed with CF shortly after birth from newborn screening.
What is newborn screening?
Since 2003 in Scotland and 2007 in the rest of the UK, all newborn babies have been screened for CF using the heel prick test. The heel prick test is offered when babies are five days old and involves taking a few drops of blood from the baby’s heel. The blood sample is then tested for several serious but rare conditions, including CF. A positive result from the heel prick test suggests that a baby might have CF, but further tests are needed to confirm or rule out a diagnosis. For CF, the sweat test is used as part of the follow-up.
Read more about newborn screening on the NHS website.
What is the sweat test?
After a positive newborn screening result from the heel prick test, a follow-up sweat test is performed to confirm or rule out a diagnosis of CF. People with CF have a higher amount of salt in their sweat compared to people who don’t have CF. This is because the gene that causes CF controls how salt moves across cells. The sweat test measures the amount of salt in sweat. It is done by collecting a small amount of sweat from the arm or leg.
Read more about the sweat test.
What is CFSPID?
CFSPID is the name to describe a positive result from the heel prick test when the follow-up sweat test does not confirm a diagnosis of CF. A person is described as having CFSPID, but this is not a condition or a disease. CFSPID stands for ‘Cystic Fibrosis Screen Positive, Inconclusive Diagnosis’. A baby with CFSPID will have been assessed by the CF team and is healthy.
My child has CFSPID. Does my child have CF?
No, your child does not have a diagnosis of CF. Your child’s screening result from the heel prick test was positive, but the follow-up sweat test did not confirm that they have CF.
What is the chance that a baby with a positive screening result has CFSPID?
For every 300 babies in the UK that have a positive newborn screening result for CF, 225 are diagnosed with CF, 15 have CFSPID, and 60 do not have either (a false positive).
What does CFSPID mean for my child’s health?
For most children with CFSPID, their health will not be affected by this result.
A small number of children with CFSPID may develop a form of CF as they grow older (thought to be 1 in 10 to 1 in 20 children in the UK), meaning that the majority of children with CFSPID remain well. We will understand this risk better as we learn more about CFSPID.
There are two main ways that CFSPID could convert to a diagnosis of CF:
- A child with CFSPID develops symptoms that seem like CF. In people with CF, a build-up of thick sticky mucus in the lungs can cause a cough and frequent and persistent lung infections. If your child has a cough that persists for more than two weeks, you should contact your GP or the CF team. They will continue to monitor and discuss your child’s growth with you.
- A child with CFSPID has a repeat sweat test that shows there is more salt in their sweat, which confirms a diagnosis of CF. A child with CFSPID will have sweat tests repeated during childhood at time points agreed with the CF team.
Some children with CFSPID have a slightly higher amount of salt in their sweat than others. Children with CFSPID who have a higher amount of salt in their sweat have a higher chance of developing CF than those with a lower amount of salt in their sweat. The amount of salt in the sweat is given as a number. A measure over 60 is high and consistent with a diagnosis of CF. A measure under 30 is considered normal. A measure between 30-60 is intermediate. Children with a number nearer to 60 have a higher chance of developing CF, and the CF team may want to see these children more often and do repeat sweat tests. You can discuss your child’s sweat test result with your CF team.
What does CFSPID mean for my child’s future?
Children with CFSPID may have changes in the gene that causes CF, which is called the Cystic Fibrosis Transmembrane Regulator (CFTR) gene. These changes might cause conditions called CFTR-related disorders. These CFTR-related disorders are not CF, but they are important to be aware of. The most clearly defined CFTR-related disorders are:
- Congenital bilateral absence of vas deferens (CBAVD), which is when the tube that carries sperm out of the testes is absent. This is a cause of infertility for men. Men with CBAVD produce normal sperm and are able to have children through assisted fertilisation (also known as IVF). CBAVD is easy to diagnose and will be discussed during adolescence with the young person, their parents, and their GP.
- Pancreatitis, which is associated with episodes of severe tummy pain. There is a simple test for pancreatitis. Tell a doctor about your child’s CFSPID if they have severe tummy pain.
The chance of having these conditions in the general population is very low. A child with CFSPID has an increased chance of developing a CFTR-related disorder compared to a child that does not have CFSPID, but we do not yet know by how much.
How often will we need to see the hospital team?
This is different for each family and you can decide this with your clinical team. Your team will explain to you the pathway of care for your child. Guidance suggests that your team will see your child at least once a year until they start school. At that point, you might discuss a plan going forward with your team or doctor.
Your team will let you know what information will be collected at an appointment, such as height, weight, results of the sweat test and results of the test for stool elastase.
When should I talk to my child about this?
As your child gets older, it is important they know about this information so they can take steps to stay well. There is no right time to talk about this, it will depend on your child and your family. The CF team can help discuss CFSPID sensitively and answer any questions with you and your child as they grow older.
What does this mean for us as parents of a child with CFSPID?
You may have questions about the chance of having another child with CFSPID. Your CF team will be able to explain this to you and your future fertility options and testing. They can put you in touch with a genetic counsellor for more detailed advice.
Because CFSPID can involve changes in the gene that causes CF (the CFTR gene), your child’s result may also be relevant to other people in your family; for example, aunts and uncles who are considering having children. They may wish to discuss this further with their GP.
This content was adapted from an existing CFSPID parent information leaflet, published December 2021, which was written in conjunction with the CFSPID working group (lead author Jacqui Cowlard, Paediatric Cystic Fibrosis Clinical Nurse Specialist, Barts Health NHS Trust).
Page last reviewed: November 2023
Next review due: November 2026
The sweat test
The sweat test measures the amount of salt (or chloride) in sweat. This is done by collecting a small amount of sweat from the arm, or sometimes the upper part of the leg, of a small baby.
How is CF diagnosed?
Find out more about cystic fibrosis (CF) diagnosis, including the processes of newborn screening, carrier testing and diagnosis in adulthood.
How is CF treated?
Thanks to breakthroughs in medication, physiotherapy and other treatments, people with cystic fibrosis (CF) are living longer and healthier lives than ever before.
Here to help
Our Helpline is available to anyone looking for information or support with any aspect of cystic fibrosis, a listening ear, or just to talk things through.