Just 20% of babies in four areas of the UK were routinely screened for cystic fibrosis before the launch of the new screening programme. The programme will soon be available in all areas of the UK, so the CF test will be offered to all newborns.
Dr Kevin Southern, reader in paediatrics and honorary consultant at Alder Hey Hospital, Liverpool, where routine screening was introduced in February 2007, answers some of your questions.
What happens during a screening test?
The test is very simple to perform. Your midwife will prick your baby’s heel when he or she is five days to a week old, and collect the few drops of blood that come out on a special card known as a Guthrie card. The card is then sent to a laboratory.
Exactly how is the blood screened for cystic fibrosis?
The lab will screen the blood for levels of a protein known as IRP. If your baby has high levels of IRP, that may indicate he or she has cystic fibrosis. But it’s not a very specific test. Some children who don’t have CF may also have high IRP. If the IRP is high, a DNA analysis of the blood spot is done to look at the baby’s genes. This will show whether the genes contain the four common mutations associated with cystic fibrosis. If these show up in the blood, the diagnosis is confirmed.
How accurate is blood screening?
Screening isn’t always this straightforward. There are many other rare mutations. If the baby has a very high level of IRP and doesn’t show the common mutations, the midwife will do another heel-prick test when the child is between three and four weeks of age. If the IRP is still raised, there’s a very good chance the child has CF.
Are there any other tests to check my child for cystic fibrosis?
Your consultant might also recommend a ‘sweat test’. The sweat glands of cystic fibrosis sufferers can’t remove the salt from their sweat, so their sweat has a very high level of salt, which we can test for.
More frequently asked questions on cystic fibrosis screening are answered on the
UK Newborn Screening Centre website (links to external site).
