Monthly Archives: August 2015

Blocked Bowel

The Press headlines this morning claim the Ministry of Health is blocking bowel screening tests. The article itself states the MoH does “not recommend” use of do-it-yourself bowel screening kits.  I can find no MoH press release relating to these kits, so I am a little confused as to whether or not the MoH is blocking anything at all.  This uncertainty aside, the issue has arisen because of the availability of bowel cancer testing kits which are self administered in the home and made available by the charity and advocacy group Bowel Cancer New Zealand/Beat Bowel Cancer Aotearoa (BBCA). There is evidently frustration within this group with respect to the government’s progress towards a bowel cancer screening program in New Zealand (there is currently a pilot underway).  My interest is not the politics, but merely to inform about the test.

The test being offered as best as I can make out is from Clinical Genomics and is their “ColVantage Home” test.  In the information on their website they give two numbers derived from trials which I believe are critical that any potential user of the test understand before they decide to use the test (indeed, not just for this test).  Those numbers are the sensitivity of the test, given as 86%, and the specificity given at 96-98%.  I expect to most those numbers are meaningless, and even to the scientist they are “minimal” in the sense no indication of how accurate these numbers are given (think “margin of errors” given in political polls).  However, let me take the numbers as gospel and let you know what they mean.

The False Positive.  I'd love to acknowledge the source, but I can't locate them.

The False Negative. I’d love to acknowledge the source, but I can’t locate it.

First, a sensitivity of 86%.  This simply means that for every 100 people who actually have bowel cancer, 86 will test positive with the home kit.  The very very important fact to note here is that a negative test does not mean you definitely do not have bowel cancer.  The 14 missed cases are called False Negatives, or Type II errors and are beautifully illustrated by this classic infographic of the doctor failing to diagnose pregnancy.  My concern with False Negatives and a “home kit” is that some people may feel falsely reassured with a negative test.  On the other hand, a test administered by a medical doctor is not simply the test, but exposure to the doctor who may see other signs or symptoms that the test doesn’t pick up.

 

 

 

False positive

False positive

On the other hand a 96-98% specificity means that for every 100 people who do not have bowel cancer 2 to 4 will test positive.  That is, a positive test does not mean you definitely have bowel cancer. The missed 2 to 4 cases are called False Positives, or Type I errors as illustrated by the diagnosis of the man in the image.

Another way of thinking about this is that all of us before a test have a certain probability of having bowel cancer.  We may get an idea of what that probability is by knowing the rates of bowel cancer amongst people like us.  In New Zealand the rates are very high – some of the highest in the world at about 0.3% or 300 per 100,000 adults.  However, risk is higher as people age, hence screening programs are targeted at older adults (over 50s in this case).  There are other risk factors.  Check out the risk calculator here.  A positive test essentially increases your risk, but not to 100%, and a negative test, decreases it, but not to 0%.  If it was me, and I was worried enough to want to have a test because of increased risk factors, I’d go and ask my GP for one.  On the other hand, if I didn’t want my wife to know (duh!) and got a kit, and it was positive, I’d also head down to the GP.

As I stated before – beware of being falsely reassured by a negative test.  However, there is also a major issue with false positives which bedevil any screening program, and even more so one in which the most at risk population are not being targeted (in this case there is nothing stopping 30 year olds having tests).  This requires a bit of maths.  Let’s pretend for a minute that the tests are only being done by people in a population with a very high prevalence of bowel cancer – say 1%.  That means that for every 10,000 people tested 100 will have bowel cancer for whom 86 the test will be positive.   Of the 9,900 who do not have bowel cancer, 198 to 396 will also test positive – ie falsely positive.  ie, in total, 284 to 480 people will test positive.  ie 22% to 30% of those who test positive actually have bowel cancer.  For the individual who started knowing they had (say) a 1% risk, they now know they have a 22 to 30% risk.  Certainly worth checking out more.

Of course, if people have these tests regularly, the proportion of people who end up having a false positive test at some time will increase (along with the proportion of people with bowel cancer who have a positive test).  ie repeat testing will increase sensitivity and decrease specificity.

Finally, if you have a history of bowel cancer in your family then don’t hesitate to ask your GP for tests and advice on what you can do to minimise your risk through improving your life style.

Two minds about funding heart research

Recently I had a knock on the door from an enthusiastic young man talking about heart research. Given that has been the focus of my research for the last 18 months or so I was delighted that someone was out there trying to raise money for research. However, my delight was, in retrospect,was tempered somewhat when I realised that the man was not representing a New Zealand based research group.

The man was collecting donations for the Heart Research Institute, an independent research group based in Sydney Australia. This is a substantial and credible organisation. I would be happy to collaborate with any of their team leaders. Looking at their website I noted one (of 12) research groups mentioned New Zealand collaborators.   I’ve written to ask if they have more. The HRI have a very professional New Zealand website which gives information on heart disease statistics in New Zealand. They indicate that they support scholarships and fellowships for New Zealanders to work with their Australian counterparts. However, I am in two minds about this group door knocking in New Zealand – one mind thinks “great” they are keen to raise money for heart research, what a good cause. The other thinks “hmmm,” don’t we have some wonderful New Zealand based heart research groups and charities – why another (not New Zealand based) one in a crowded field seeking money from a limited pool of discretionary spending?

Perhaps, to help the people of Canterbury and wherever else funds are being solicited from to make up their own minds, I can remind people of four great charitable organisations supporting heart research in New Zealand.

Heart Foundation of New Zealand: This is a wonderful organisation with a long history of supporting research in New Zealand as well as supporting individuals within New Zealand. They are the group behind the “Heart Foundation Tick” on food labels. Their website is really worth checking out… I just learnt about the “Two Ticks” now appearing on some labels. For the likes of a researcher like me they provide small, but very important, grants that enable important questions to be answered. Indeed, I have just had a paper published which a Heart Foundation grant made possible. In that paper we show that one of the latest guidelines on how to use a blood marker (used in most New Zealand hospitals) to rule out someone having a heart attack are flawed. I note, that they have in large letters on their web site that they do not do door to door fund raising.

Christchurch Heart Institute: CHI is a research group and charitable organisation within my own department, the Department of Medicine, at the University of Otago Christchurch campus (known to most Cantabs as “the med school”). Headed by Professor Mark Richards it is a world renowned group. I have the privilege (a little daunting given just how incredibly intelligent these people are) to collaborate with CHI on a number of clinical projects. The publication I mentioned was one of them. Another project, just kicking off, is investigating markers of acute kidney injury within people who have acute heart failure. They have recently expanded into social media – so you can follow them on facebook.

Canterbury Medical Research Foundation:  CMRF is a wonderful organisation – they are one of the three major sponsors of my own fellowship. My own prejudice aside, CMRF have been supporting research in Canterbury for over 50 years. One aspect of the CMRF that really impresses me is that they understand the need to support researchers and just “let them get on with it.” Cantabrians may recognise their recent campaign that has included some impressive billboards. One important plank of CMRFs work in Canterbury is their subsidiary the New Zealand Brain Institute which does important research into stroke, Alzheimer’s and Parkinson’s disease.

Emergency Care Foundation: The ECF supports research in the Emergency Department of Christchurch hospital including research into the rapid rule-out of heart attacks for patients presenting with chest pain.  I’m fortunate enough to be involved in that research and the role out of new diagnostic pathways to all emergency department in the country.  ECF also support research into the health affects of the Christchurch earthquakes.  ECF are another of my major sponsors.

Some logos of the great local charitable organisations supporting heart research

The transplant smile

Source Deviant Art

Source Deviant Art

“His mega-watt smile could power the Auckland grid” was how Herald columnist Wynne Gray so eloquently described this morning Joeli Vidiri after his kidney transplant.  In the meantime across the Tasman my long term colleague and head of Nephrology at Prince of Wales Hospital in Sydney, Prof Zoltan Endre, is celebrating 50 years of the transplant unit. There is a lovely story of a smiling Carolyn Hochkins who has survived 42 years with a kidney transplant.  Invaluable!

Transplants have become “normal” and rarely make the news unless it is of a famous face or a celebration such as in Australia this week.  They are far from “normal” for the recipients.  They are life changing – not simply a change from being tied to a dialysis machine for many hours a week, but better all round health.  The machine is merely supportive and it doesn’t manage to do everything a kidney can do.

Congratulations Joeli, Congratulations Carolyn, Congratulations all you donors and donor families, Congratulations all you dedicated nephrologists and surgeons that have made the kidney transplant a routine life changer.