Cystic Fibrosis
Approximately one in every 1,500 infants born in Ireland may have Cystic Fibrosis (CF). CF is also an autosomally inherited condition, both parents carrying an abnormal CF gene. As a consequence of the condition, thick mucous secretions are produced by a number of organs in the body including the lungs and the pancreas and it is this thick, mucous secretion that causes the problems. The thick secretions in the lungs may become infected causing damage ultimately and in the pancreas causing digestive problems. Consequently, infants with CF may not gain weight and have frequent chest infections.
Newborn screening means that infants with CF are identified earlier; they can be treated with a high energy diet to improve weight gain, and physiotherapy and medicines to improve lung function and gut absorption. Although a child with CF may still become ill, early treatment does improve their quality of life, significantly reduces the time that they have to spend in hospital and they live healthier and longer lives.
The screening programme for CF measures the plasma level of immunoreactive trypsin (IRT). IRT is normally excreted by the pancreas but in individuals with CF this is ‘regurgitated’ back into the blood due to the thick mucous secretions which block the pancreatic ducts. IRT levels remain high in blood for about the first six months of life. Because of this, IRT can be used as a first line screening test but it is not very specific, with a relatively high false positive rate. DNA analysis on the original newborn screening card significantly improves the specificity but up to 2% of carriers of CF born each year will also be detected. The measurement of sweat chloride (Sweat test) is used to confirm the diagnosis.
As with the other conditions, not all infants with CF will be detected by the newborn bloodspot screening programme. There are a number of different clinical varieties of CF, some of which have very benign courses and may not require treatment.
Action following detection of raised result
If the bloodspot IRT is raised and greater than the 99%ile, a blood spot circle from the newborn screening card is referred for a 38 panel CFTR mutation analysis. The results of the mutational analysis are returned to NNBSL for reporting (No results will be issued by the reference laboratory). If no mutations were identified a report will be issued stating <CF not suspected> and no further clinical action will be taken.
If one or two CFTR mutations are identified the following action will be implemented:
1. The Clinical Liaison Officer (NNBSL) will:
- confirm the demographic data on the NSC, and contact the designated Maternity Unit Liaison Officer or PHN to verify the contact details of the parents and their preferred first language;
- use the address of the parents to determine which the HSE designated CF Centre the baby will be referred to;
- Contact by phone the CF Nurse Specialist in the appropriate HSE designated CF Centre giving her full details of the baby, contact details of the parents, the results of the IRT and mutation analysis and any other relevant clinical information;
- immediately fax a copy of the NBS report, containing the infant's contact details and the NBS result, including the identified CF mutations
2. CF Nurse specialist will then:
- Inform the CF Paediatric Consultant on duty and arrange for a Sweat test to be performed the following day
- Contact the parents, advising them that their baby is at risk of having CF and that further investigations including a Sweat test are required and arrange for them to attend the next day
3. On arrival the baby will be examined and the Sweat test performed. A further heel-prick blood sample may be taken and sent to the Newborn Bloodspot Screening Laboratory for a repeat IRT. When the results of the Sweat test become available later in the day, the parents will meet with the consultant who will give them the results of the further investigations
- If two CFTR mutations are identified and the Sweat test is positive a diagnosis of CF will be made and the parents informed
- If two CFTR mutations are identified and the Sweat test is either equivocal or negative, CF is still suspected; further tests will be required to confirm the diagnosis
- If one CFTR mutation is identified and the Sweat test is normal the parents will be advised that <CF is not suspected> but that their child is a carrier. They will be offered Genetic Counselling at a later date and will be referred to the National Centre for Human Genetics at Out Lady's Children's Hospital, Crumlin
- If one CFTR mutation is identified and the Sweat test is equivocal the parents will be advised that further tests will be necessary to out rule CF
- If one CFTR mutation is identified and the Sweat test is positive they will be advised that <CF is suspected> and that a further expanded CFTR mutation analysis will have to be undertaken
4. The CF Nurse Specialist will inform the NNBSL of the final diagnosis, that the infant has been reviewed by the CF consultant (who now assumes responsibility for the infant), and of the result of the Sweat Test.
Newborn Screening for Cystic Fibrosis is now complete.
