Screening
Stuff has a story (borrowed from the West Island) headlined “Over 40? Five tests you need right now”.
You might have expected some reference to the other recent news about screening: that the US Preventive Services Taskforce has now joined the Centers for Disease Control in recommending universal screening for HIV (as TVNZ reported). It’s not clear if New Zealand will follow the trend — HIV infection in people not in high risk groups is less common here than in the US, so the benefit compared to more selective screening is smaller here. This illustrates the complexities of population screening. Not only does the test have to be accurate, especially in terms of its false positive rate, but there needs to be something useful you can do about a positive result, and screening everyone has to be better than just screening selected people.
So, let’s compare the suggestions from Stuff’s story to what national and international expert guidelines say you need.
Two of the tests, for high blood pressure and high cholesterol, are spot on. These are part of the national 2012/13 Health Targets for DHBs, with the goal being 75% of the eligible population having the tests within a five-year period. The Health Target also includes blood glucose measurement to diagnose diabetes, which the story doesn’t mention. The US Preventive Services Taskforce also recommends blood pressure and cholesterol tests, though it recommends universal diabetes screening only after age 50 or in people with high blood pressure or people with risk factors for diabetes.
One of the tests recommended in the story is a depression/anxiety questionnaire, for diagnosing suicide risk. Just a couple of weeks ago, the US Preventive Services Taskforce issued guidelines on universal screening for suicide prevention by GPs, saying that there wasn’t good enough evidence to recommend either for or against. As the coverage from Reuters explains, these questionnaires do probably identify people at higher risk of suicide, but it wasn’t clear how much benefit came from identifying them. So, that’s not an unreasonable test to recommend, but it would have been better to indicate that it was controversial.
One more of the tests isn’t a screening test at all — the story recommends that you make sure you know what a standard drink of alcohol is.
The top recommendation in the story, though, is coronary calcium screening. The US Preventive Services Taskforce recommends against coronary calcium screening for people at low risk of heart disease and says there isn’t enough evidence to recommending for or against in people at higher risk for other reasons. The American Heart Association also recommends against routine coronary calcium screening (they say it might be useful as a tiebreaker in people known to be at intermediate risk of heart disease based on other factors). No-one doubts that calcium in the walls of your coronary arteries is predictive of heart disease, but people with high levels of coronary calcium tend to also be overweight or smokers, or have high blood pressure or high cholesterol or diabetes — and if they don’t have these other risk factors it’s not clear that anything can be done to help them.
As an afterthought on the coronary calcium screening point, the story has an additional quote from a doctor recommending coronary angiography before starting a serious exercise program. I’d never heard of coronary angiography as a general screening recommendation — it’s a bit more invasive and higher-risk than most population screening. It turns out that the American College of Cardiology and the American Heart Association are similarly unenthusiastic, with their guidelines on use specifically recommending against angiography for screening of people without symptoms of coronary artery disease.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »
“if they don’t have these other risk factors it’s not clear that anything can be done to help them”
That should be subject to empirical testing, though, shouldn’t it? I wonder if a screening trial for CAC (like we have for cancer) is a sensible idea or not?
12 years ago
Yes, it should be subject to empirical testing. It’s not easy — you’d probably need a large-scale cluster-randomised trial (as was done for mammography).
In the MESA study of atherosclerosis and coronary calcium we actually suggested randomising whether participants were told their coronary calcium or not. It didn’t fly.
There have been randomized trials of statins in people with high coronary calcium, looking at progression, but even this has mixed results
12 years ago
That is an interesting point of trivia about MESA. I had not heard that piece.
I don’t think the study would need to be American to answer the questions. I do some work with the HNR study and they were able to not report CAC values to participants (and they used a very similar screening approach).
The harder piece is what intervention might be sensible. It’s unclear that statins will help all that much in primary prevention of events in participants with normal cholesterol. Bypass may help if we get more sophisticated and look at the specific pattern of lesions in the coronary arties but that is a fairly drastic surgery.
My pet hypothesis is low dose aspirin would be useful but it is not easy to prove nor is it clear that medium/high risk participants would not benefit from this as a matter of course.
I do agree with you that CAC screening definitely needs more evidence before it becomes routine. If nothing else there is a radiation dose and, while doses have dropped, it may not be a zero risk procedure.
12 years ago
The post above is from me (missing last name). I apologize for dropping my last name. I typically do so online and sometimes I slip into automatic.
12 years ago