Dr Peter Moore: Sadly, life and medicine are never simple

Prevention is a little more complicated when it comes to screening

Prevention is a little more complicated when it comes to screening - Credit: Getty Images/iStockphoto

It sounds obvious; prevention is better than cure. Many diseases must be treated early so why don’t we screen for more diseases, pick them up early and cure them?

As a certain meerkat might say ‘simples’. Sadly, life and medicine are never that simple.

Screening does not work as a scatter gun, loads of tests to see what happens. It must be targeted at a specific disease.

Also screening involves taking healthy people, testing them and telling some of them that they may not be healthy after all.

This will have a psychological effect even for the people who turn out not to have anything wrong.

In 1968, the World Health Organisation asked James Wilson, the Chris Whitty of the day, and Gunner Jungner from Sweden to write report into screening.

They came up with some basic questions to ask about any screening programme. These are still relevant today, over 50 years later.

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The first question ‘is the disease important?’ There is no point in screening for a disease which gets better by itself with no long-term effects.

We also need to understand the ‘natural history’ of the disease. How does it progress if not treated?

There must be an early stage when it does not produce symptoms. If the disease immediately gives symptoms people will go to the doctor anyway. If they don’t, we need education not screening.

We need a simple, reliable test. There is no point in a screening process that requires five days in hospital for everyone.

The test must not have too many false positives or the NHS will be overwhelmed with healthy anxious people but too many false negatives would give a false reassurance to hundreds. The disease must have an effective treatment.

It would be cruel to screen for a serious illness, tell people the bad news and then explain there is nothing that can be done.

Even in 2020 there are still some diseases where treatment is disappointing.

If treatment is effective, we should only screen if we know that early treatment matters. There are some treatable diseases where it is safe to wait until there are symptoms.

There are also political decisions to be made. Who should be screened?

If a disease is common in older people but rare in younger people, should we only screen the over-60s?

There will always be a borderline. If we screen the over-60s will the Government be accused of allowing the 59 year olds to die?

If it is less serious in the elderly do we stop screening at 70? Will the Government then be accused of ageism?

How much does treatment cost? We cannot screen for a disease, find thousands of cases and then not have the facilities in the NHS to treat them all.

Only set up a screening programme when the hospitals have a system in place to treat the positive cases.

We also need to be careful with statistics. Suppose we have a test for a terrible fatal disease which showed that people who were tested survived over three years longer than anyone not tested. Sounds good? But suppose this terrible disease was always fatal after five years.

If diagnosed after one year people survive for four years. If we do not pick it up for four years, people only survive a year. Sadly, in this case screening makes no difference despite the optimistic sound bite.

Screening is often not a one-off. If the screening is all clear we need to decide when to arrange the next test.

Luckily, we do not expect politicians to make difficult decisions about screening. There is a UK National Screening Committee to advise ministers.

They look at the evidence and decide on any new screening programme. And so, our NHS screening programme such as cervical smears, breast screening and the ‘poo test’ have good evidence. Like certain cosmetics they are worth it.

Prevention is important when it comes to exercise, not smoking, keeping the weight down and living a healthy lifestyle. But prevention is a little more complicated when it comes to screening.