Should you have a colonoscopy?

Colonoscopy is currently regarded as the gold standard in detecting bowel cancer, which is amongst the most common cancers in the country. This type of cancer is often slow growing and if detected early, can be nipped in the bud before it goes on to do its nasty work. A lump in the colon that has not yet become cancerous is referred to as a ‘polyp’. As stated, colonoscopy is the gold standard test to diagnose or rule out bowel cancer, but the approved method for mass screening is the ‘Faecal Occult Blood Test’. This means testing a small specimen of stool for microscopic amounts of blood, using an approved testing kit (the ‘FOBT’). Approved kits can be obtained from a pathology service via a GP, or can purchased from your chemist or even via the internet. If you are turning 50 or 55, the Government will mail you an FOBT kit. The latter is provided  via the ‘National Bowel Cancer Screening Program’. The trouble with the FOBT is the false negative rate, ie the kits can miss up to 33% of the cancers, mainly because colon cancers, especially early ones, don’t bleed enough to be detected.

So if you are really concerned about minimising the risk of bowel cancer, you can’t rely just on one normal FOBT result. A way around this is to repeat the FOBT on an annual or more frequent basis. Another option is the ‘CT colon’, which is a CT scan of the bowel costing about $300 from various Radiology Services (usually, no Medicare Rebate is available). CT colon will detect polyps above 2mm in size, but cannot determine if they are benign or otherwise. You’ll then need to have the colonoscopy. Its important to note that Colonoscopy itself is not without risk of complications, albeit low. Discuss these with your doctor.

One of the key questions relates to the optimal frequency of colonoscopy screening, if a pre-cancerous lump is found. I’ve seen patients  recalled after only 12 months for what I’ve understood to be simple benign polyps. As with anything, the answer to this lies in the research and guidelines. The National Health and Medical Research Council provides guidelines on this aspect of colon cancer screening. Refer page 10 of this document, as dated December 2011. Therein the guideline is for a five yearly follow up for ‘low risk’ polyps:
“follow-up of patients with one or two small (<10 mm) tubular adenomas, the first surveillance colonoscopy should be performed at five years …. Options for subsequent surveillance are ten-yearly colonoscopy, or FOBT at least every two years”

However, the guidelines do go on to state that timelines may need to be individualised. This means the follow up can be discussed with your gastro-enterologist.

There is a privately run colonoscopy clinic describing describing itself as a Program targeting Bowel Cancer, which some patients are confusing with the offical government ‘National Bowel Cancer Screening Program’. The difference of course is that the former is a privately run fee-based service using colonoscopy as a screening tool, whereas the latter is a government run mass screening Program relying on FOBT as its methodology. Offically, colonoscopy has not been accepted as a mass screening method for bowel cancer but of course it is the gold standard.

Finally, some mention should be made of the risk of bowel cancer. The risk of developing it, as stated in The National Health and Medical Research Council’s Guidelines for the Prevention, Early Detection and Management of Colorectal Cancer (2005) are:

• 1 in 100 at age 50, of developing it over the next 10 years
• 1 in 50 at age 60, of developing it over the next 10 years

I have tabulated more detailed statistics here, for download.

That meshes with informal advice received from a gastro-enterologist some years ago, where it was suggested to have a screening colonoscopy at age 50, then again at age 60. That should dramatically decrease the risk of succumbing to bowel cancer in your 50’s or 60’s. He advised that screening beyond that date is an individual decision, ie he didn’t advocate further colonoscopies purely for screening purposes after that date.