Screening complications

Regular readers will know that I have concerns about many tests used in the UK for screening. Screening tests are used when people are well, with no symptoms of disease. The aim of screening is to pick up a disease process at an early, pre-symptomatic stage such that an effective intervention can be used to prevent complications.

Real life is rarely that simple. A while ago I was asked (live on radio) for an example of a perfect screening test. Unfortunately, all I had to offer was a long silence as I tried (and failed) to think of one. Instead screening tests offer a balance of probabilities, and the risks and benefits of interventions which can then be offered are usually more complicated the more one examines them. (I’ve just finished reading Sir Muir Gray and Dr Angela Raffle’s excellent book Screening, Evidence and Practice. Raffle is a public health consultant, and Gray was the Programmes Director of the  UK National Screening Programme from 96-07. The first line of the preface is ‘All screening programmes do harm’.)

The practical outcome for healthcare workers must be that people are given better information about screening tests and that they are not pushed in to accepting tests. The aim of the NHS should not be to frighten or cajole people into screening but to allow adults good information to make their own choices.

There is a good paper this week in the British Medical Journal about how healthcare professionals should communicate about screening tests, I quote:

” People are offered a wide range of screening tests by diverse providers. For example: maternal and child health services screen for genetic conditions and developmental problems; general practitioners screen for cardiovascular risk factors; NHS programmes screen for bowel, breast, and cervical cancer; and commercial providers offer various health assessments, including body and gene scans. Provision of tests is not well regulated, and there is a bewildering amount of information of variable accuracy in the public domain…

Debates about communication have tended to consider two types of approach, which we call ‘be screened’ and ‘analyse and choose’. We consider their problems and propose a third approach, ‘consider an offer’.

I suspect there will be major problems with how this very reasonable approach of encouraging people to ‘consider an offer’ will be translated into use the health service. When I declined antenatal testing for Down’s syndrome during pregnancy this was taken as ’patient refused’ which has negative connotations. Healthcare staff were keen to ensure that I knew ‘the risks’ of what I was (not) doing. 

However, ‘the risks’ of the problems and complications of screening tests in this situation are often not explained quite so emphatically. We tend to think that not having an intervention is far ‘riskier’ than having it. This is a fault of medicine which too often promotes thoughtless ‘more is more’ approaches. 

My decision about not having this antenatal testing was based on my knowledge of the rate of false positives and negatives of the test, the knowledge that if my child had Down’s syndrome then I would not wish a definitive diagnosis with amniocentesis (which has risks to the pregnancy), that I would not have an abortion and that I did not think that prenatal diagnosis would be likely to offer me or the baby much advantage. I concluded that there was more likely to be harm done with this test. Yet many women only realise the extent of the dilemmas they face when a result is returned as being potentially abnormal.

The very least people should expect about screening is for it to come with neutral, balanced information which spells out the uncertainties and evidence about it. And which does not assume that having a screening test is the ‘right’ decision.

Margaret McCartney’s Blog

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