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Making The Diagnosis

Usually by the time you are looking at our website, a diagnosis of Cystic Fibrosis has been made for you or your child. However on some occasions the diagnosis is not so straight forward so this page is to help you understand this diagnostic process and how it might relate to your child. If you have any questions then please ask your CF team for further explanation.

Since 2007, Newborn screening has helped to make an early diagnosis of CF. Most new cases of CF are identified in this way. This uses the routine screening for lots of conditions in newborn babies using the heelprick blood spot tests at Day 6 of life. The test measures Immunoreactive trypsinogen (IRT) levels in the blood.  Samples with high IRT levels will go for CF gene mutation  screening so results can take up to 4 weeks to come through and sometimes a second heelprick test is needed.  Any positive result is notified to your nearest CF centre.

Have a look at the flow chart below for more information.

To have CF, you need to have two CF causing genes, one from your mother and one from your father. CF genes (mutations) code for the production of a protein called CFTR ( Cystic Fibrosis transmembrane regulator) in body cells. CFTR allows salt (Chloride) and with it water to pass across cells. CFTR does not work properly in people with cystic fibrosis and exactly why it doesn’t work is decided by the exact CF gene mutation combination you have (called your Genotype). Lots of exciting new drugs are targeted straight at the CFTR abnormality – see the section on  novel therapies in the CF Trust link.

If your baby has a positive screen, the CF Nurse Specialist will liaise with your Health Visitor to discuss the result and arrange a joint visit to your home to explain the result and what needs to happen next. The diagnosis of CF will need to be confirmed, so an appointment with a CF specialist consultant will be made soon afterwards  and some further tests will be arranged. These include a blood test (to confirm the screen result), a stool (poo) test, to find out how well your baby’s digestive system is working, and at a later date a sweat test.

We now know there are different types of CF which range in severity. Identifying the specific CF genes can help us understand more about your baby’s CF  and some of the newer treatments are matched to specific CF genes.

Sometimes there can be uncertainty after screening and this can be frustrating for parents.  These babies are termed CF screen positive, inconclusive diagnosis (CFSPID)  and we advise that they are followed in our clinics in order to ensure the baby remains well.  If this is the case for your child we will support you with this uncertainty and pull together all the information from follow up tests  to help you understand the information available for your child.

National Screening Algorithm

Outcomes are predicted for a population of 10,000 newborn

The few cases of CF that are missed by screening  (screening identifies about 95% of all cases ) will present later with illnesses that suggest CF. These may include recurrent chesty problems, poor weight gain with bulky, fatty stools  or later in life with male  infertility. Any cases that raise concern, particularly with a family history should be referred for a sweat test.

Sweat testing helps to confirm the diagnosis of CF in the majority of patients especially if the CF gene type is not clear. Everyone with suspected CF should usually have a sweat test at some time. These can be done when your baby is very young but in order to get enough sweat, we usually wait until babies are over 5 kgs before attempting to save needing to repeat it.

We use a technique known as the macroduct system which takes a couple of hours and is not uncomfortable. In paediatrics these are generally done in our Bramble day case. Two Sweat Chloride (salt) levels of  that are high (more than 60mmol/ l) confirm a diagnosis of CF.

There are rare occasions when a sweat test can be within the normal range despite a diagnosis of CF – results will be discussed with you on an individual basis. Please ask the team if you are unsure about your own or your child’s results.

For older siblings, who have not been screened, we will ask for a sweat test rather than genetic testing – this avoids identifying carrier status which is something better delayed until the child is old enough to decide whether they wish to know whether they carry a CF gene.

If you have one baby with CF and become pregnant again, early screening in pregnancy can be done or umbilical cord blood can be taken at the time of birth  for genetic testing – feel free to discuss options for future pregnancy with your team to support you with these decisions.

If both CF genes are  not identified at screening, we will send you or your babies blood to a lab in Manchester for an extended CF gene screen. This can take many months to get a result. Many of the exciting new CF treatments target  specific CF gene types with the aim of correcting CFTR function, so knowing your gene type has become more important. If we cant find  a second mutation this does not exclude the diagnosis as new rare mutations continue to be discovered. The sweat test and pattern of illness are important in such situations in making the diagnosis .

If you are parents of a child with CF  and planning a further pregnancy then referral for genetic counselling may be helpful to guide your decision making. You can discuss options available including  IVF with preimplantation screening, early pregnancy screening (CVS) performed around 10-12 weeks gestation or amniocentesis  later in pregnancy. Talk to your team and we can support you with this.