Expensive Liquid Cytology Is No Improvement

[BillyJoe]

http://www.greenjournal.org/cgi/content/abstract/111/1/167

This is the summary of the results of a meta-analysis of "eligible" studies comparing cheap conventional cytology with expensive liquid-based cytology published between 1991 and 2007:

Liquid-based cervical cytology is neither more sensitive nor more specific for detection of high-grade cervical intraepithelial neoplasia compared with the conventional Pap test.


Unfortunately, I cannot access the full article unless I become a subscriber to ACOG or pay $20 for a one day access, so I cannot assess whether the conclusion is justified by the data.

Does anyone have access?

Anyway, if the conclusion is justified, I have a question:

Why does conventional medicine rush in to implement a new expensive test when there is no evidence of a need to do so. Apparently, many labs in the USA have already stopped offering the previous cheap cytology test. What's a bet they won't be going to back to it in the face of this evidence.


BillyJoe

[Ivor the Engineer]

[QUOTE=BillyJoe;3334373<snip>

Why does conventional medicine rush in to implement a new expensive test when there is no evidence of a need to do so.

<snip>

BillyJoe[/QUOTE]

Probably because it can make more money than the old test and provides product differentiation (http://en.wikipedia.org/wiki/Product_differentiation) in a saturated market (http://en.wikipedia.org/wiki/Market_saturation).

[Dragon]

Well, the NHS in the UK now uses LBC - my understanding is that they changed from PAP because the evidence indicated that it is more sensitive and specific. They certainly don't have an interest in spending more money for no extra benefit.
Mrs D is a nurse colposcopist and knows the UK cervical screening programme inside out, I'll ask her later. She might also have access to the full article.

[Ivor the Engineer]

It appears LBC reduces the number of spoiled samples compared to PAP.

http://www.cancerscreening.nhs.uk/cervical/lbc.html

How will women benefit from the introduction of LBC?

The reduction in inadequate rates from using LBC will be of considerable benefit to women in terms of reducing anxiety, uncertainty and the need for repeat smears.

Inadequate smears are those where no result can be issued and include those where blood or other matter in the sample makes it impossible to see the cells on the slide properly. In these cases, women are invited back for a second test. The number of 'inadequate' test results will fall and therefore so will the number of women who need a second test. A faster turnaround time in the laboratory also means that women will get their results more quickly.


How will LBC benefit staff?

LBC will

reduce the number of inadequate smears (for example, the introduction of LBC at the pilot sites reduced the reported rate of inadequate smears from 9 per cent to 1-2 per cent.)

reduce the pressure on a skilled workforce (fewer inadequate smears and clearer to read samples. Nationally, the workload would be reduced from 4.2 million slides per annum to 3.9 million slides per annum).

reduce levels of anxiety in women who accept their invitation for cervical screening (quicker reporting time and a reduction in the number of women who are invited back for a repeat smear)

save money overall

[Dragon]

Ivor, you're right - I'd just spoken to Mrs D on the phone (before reading your post) and she said exactly that.

"Inadequates" were running at 10-15% compared to 1-2% with LBC (she knows this stuff without having to look it up). This means that fewer women have to be recalled for another smear (as your quote says some of them won't turn up because the experience can be off-putting and cause anxiety) and in amongst those "inadequates" will be some cancers - necrotic cells can make the smear difficult to read. Another benefit of LBC is that it is apparently better at picking up glandular abnormalities as well as the epithelial changes it was designed for.

[BillyJoe]

Inadequate smears are those where no result can be issued and include those where blood or other matter...


:cool:

[BillyJoe]

http://www.abc.net.au/rn/talks/8.30/helthrpt/stories/s1553947.htm

This study is just on two years old and, unfortunately, it is only an interview with the researcher about the results:

Elizabeth Davey: We found no difference in an analysis of over a million slides in the rates of unsatisfactory smears. We found very little evidence that there was any difference in the types of cells they classified, we found some very minor differences when we examined quality separately. We classified studies into quality groups and we found very little difference across those quality categories and we found only four studies from which we could assess accuracy – and in those four studies that were sufficiently well designed, we found no evidence that liquid based cytology was more accurate than conventional.


I wonder if the new study has anything to say about whether the rates of unsatisfactory smears was any different.

[BillyJoe]

Here is an updated review dated Jun 2007 by the same author and is the actual report this time:

http://www.bmj.com/cgi/content/full/335/7609/31?rss=1

Fewer unsatisfactory slides were found for imager read cytology than for conventional cytology (1.8% v 3.1%; P<0.001).


The figures for the UK were 1-2% v 9%!!!

Also:

The ThinPrep Imager detects 1.29 more cases [7.7 v 9.0 per thousand] of histological high grade squamous disease per 1000 women screened than conventional cytology...3.1 more biopsies per 1000 women screened were required to detect these cases