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Thursday, 3 May, 2001, 11:45 GMT 12:45 UK
Screening: What should we expect?
cervical screen screen
A complex picture: but is it cancerous?
The Leicester cervical screening errors reinforce the point that no test of this type can be 100% accurate.

BBC News Online examines what the public can expect from cancer - and other screening tests.

Some patients think of their mammograms and cervical smears in absolute terms - a positive or negative finding is 100% reliable, they believe.

But every test has an error rate - it will miss some patients who have the disease, and wrongly diagnose some who are not actually ill.

Both of these can have serious consequences for the patients.

Those are the drawbacks of tests which are acknowledged to save thousands of lives in the UK every year by picking up cancers when they are in their early stages, and easier to treat.

Latest Imperial Cancer Research Fund figures suggest that the programme is saving approximately 1,300 lives a year.

We should stop using the word screening altogether because for most people it relates to the cinema

Dr Muir Gray, national screening committee
In the case of cervical screening, the Leicester audit is one of the first to be carried out without the hint of a scandal prompting it.

As such, it is possibly an accurate reflection of exactly what we can expect from cervical cancer screening.

The deaths and unneccessary surgery revealed here could be mirrored by other audits elsewhere in the country.

People need to be made aware of the risks and the drawbacks of screening for disease as well as the benefits, according to a leading UK doctor.

Dr Muir Gray, director of the Institute of Health Sciences in Oxford - and an acknowledged expert on screening - says people have come to expect that screening for conditions like cancer is a straightforward and totally reliable process.

Dr Gray says people need to be informed that screening programmes are not 100% sensitive and not without risk.

The risks and limitations have to be clearly spelled out in people "even at the expense of limiting coverage", he said.

'Informed choice'

"Informed choice by the individual must form a central part in any population screening programme in future," he told BBC News Online.

Detecting disease through screening may have major consequences in terms of subsequent treatment - though not everyone appreciates that when they undergo the initial test.

In the past, Dr Gray said, the focus of health care has been on the benefits and on cost-effectiveness.

In the 21st century people are much more concerned about the risks and limitations of what is done to them.

Dr Gray says: "We should stop using the word screening altogether because for most people it relates to the cinema.

"Instead we should be talking about risk reduction programmes so people have reasonable expectations."

The future

The human element of cervical screening is one reason why the error rate cannot be radically reduced in the short term.

Every slide - often a mush of detritus as well as the cells themselves - must be checked by eye for the odd-shapes and configurations which suggest cancer or pre-cancer.

In many cases, these are easy enough to miss, even to the most experienced professional.

Some abnormalities, which figure only tiny variations in cell appearance, are very difficult to spot.

And in some borderline cases, there may only be a couple of suspect cells in a smear carrying many thousands.

In the future, methods are being developed which should improve the error rate.

One is liquid-based cytology, a way of processing the smear samples which could lead to a computerised and far more reliable checking scheme.

These processes are under test at the moment, and could mean a less traumatic future for the screening process.

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See also:

20 Oct 00 | Health
'Screen for baby infection'
29 Sep 00 | Health
'No benefit' to cancer test move
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