Newborn screening for cystic fibrosis: do we need a second IRT?
- Correspondence to:
Prof. J F Price
Paediatric Respiratory Medicine, King’s College School of Medicine, King’s College Hospital, Denmark Hill, London SE5 8RX, UK;
Commentary on the paper by Massie et al (see page222)
Newborn screening for cystic fibrosis (CF) has been possible since 1978, but national screening programmes have proved highly contentious and as yet have only been adopted in a minority of European countries and North American states. The main issue has been whether early diagnosis through screening results in long term clinical advantage, particularly in lung function. Recently the balance of benefit against harm has tipped in favour of screening,1 providing that early diagnosis is followed by high quality care in specialised centres.2 Screening programmes have been introduced in Northern Ireland, Wales, and Scotland. Only about 20% of babies are screened for CF in England, but a national screening programme is due to be implemented over the next three years. A good screening programme should identify the maximum number of cases that are likely to be severely affected, ensure that as many as possible of the missed cases are mildly affected, detect as few unaffected carriers as possible, allow for ethic diversity, and generate a minimum of anxiety. Three options are available; IRT-IRT, IRT-DNA, and IRT-DNA-IRT.
IRT-IRT involves measurement of immunoreactive trypsinogen (IRT) during the first week on the Guthrie blood spot and repeating the measurement at 3–4 weeks in those with initial high levels. This protocol for screening was introduced in East Anglia in 1979. The sensitivity of a raised 3–5 day IRT is high, but the positive predictive value is low. Because blood levels of IRT decay slowly …