Dr. Colm Henry:

It is an interesting question. Every screening programme balances the risk between false negatives, on which much of the discussion has been focused, but there is less focus on the false positives, which can be very harmful too. Over-referral of patients for interventional investigation can be harmful too. We know that not just from the cervical screening programme but from other screening programmes. In the breast screening programme, for example, the aim is to keep the recall rate below 7%. Otherwise, they are over-referring patients who are otherwise healthy, coming in to a screening programme, volunteering their time to partake in a screening programme for interventions and investigations which may be harmful. Every screening programme calibrates between the need to pick up as many precancerous changes or early cancer changes in the case of breast cancer against the risk of over referring people. In the case of the cervical screening programme, for every 1,000 women screened, there are 20 abnormal findings of which the liquid-based cytology picks up 15, but once we move to HPV screening, that will improve to 18, as it is a much more sensitive screening test than cervical cytology. We expect to see an improvement in the sensitivity without the expense of over-investigating and subjecting people to unnecessary harmful investigations.