False positives are one of the many banes of screening programmes. In the US, advertising for people to come to private clinics for expensive CT scans, to screen people for lung cancer is common and, of course, legal. Here in the UK, several private companies advertise their services despite COMARE saying that “we have strongly recommended that services offering whole body CT scanning of asymptomatic individuals should discontinue to do so. .. We have concluded that there is no evidence that CT scanning for lung conditions is of benefit. ”

This advice has made little difference in the UK where the scans are still on offer at several clinics.

But still, the US is starting to keep consistently producing evidence questioning what is, over there, an ingrained practice. This paper from the Annals of Internal Medicine suggests that the risk of a false positive after one scan is 21% and after two scans, 33%. When one considers the follow on from a ‘positive’ result (further invasive tests, the effects on oneself and family) this is highly significant.  While it may be be (currently) legal to offer and advertise screening CT scans in the UK, people should be told the whole truth about them. The US study says it’s the first to report on this type of cumulative harm, as part of an ongoing trial into screening in smokers. It’s exactly the kind of information that is needed for balance.