Background: screening is often thought to have no downside, but this isn't true
Before dealing with the specific evidence, it is worth a quick review of why the benefits and costs of screening are often misunderstood. The basic problem is that public perception sees only the potential benefit (diseases can be spotted early and therefore treated more effectively) and regards screening as costless with no possible downside.
There are two key problems with the view that screening is all upside. One is that the intuition that early diagnosis helps is not always true and needs to be proved with real statistics. The other is the perception that there is no downside. This is wrong for two separate reasons: one is that some diagnostic methods cause harm (CAT scans use x-rays which cause a small increase in the cancer rate in those exposed to them); the other is that even benign diagnostic methods can result in false positives and can diagnose issues which would never have cause the patient problems. Both result in unnecessary treatment which causes harm to patients.
The public perception is heavily influenced by sources that are not unbiased. As one study concludes (my emphasis):
... information pamphlets, Web sites, leaflets distributed to doctors by the pharmaceutical industry, and even medical journals often report evidence in nontransparent forms that suggest big benefits of featured interventions and small harms. Without understanding the numbers involved, the public is susceptible to political and commercial manipulation of their anxieties and hopes, which undermines the goals of informed consent and shared decision making.
One of the clearest examples of the actual downside from screening is seen in the statistics for screening for prostate cancer (see the question and answer Does screening for prostate cancer save lives? for details). But even screening for breast cancer is controversial (see the alternative positions in answers here Is routine screening for breast cancer for asymptomatic women worthwhile? ). In both these cases the downside comes because the risks associated with treating false positives are large enough to balance of even overwhelm the gains from early diagnosis.
So the apparent logic of screening must be tested by careful statistics that need to weigh up the benefits and costs associated with the programme of screening. We should insist that the evidence is gathered and analysed rather than just accepting the apparent logic.
Routine screening of healthy people doesn't seem to have any benefits
The study (summary here, full study here) that prompted the news story triggering the question is a Cochrane Review (a meta-analysis of the best existing studies from the medical literature).
The summary explicitly addresses the perception that screening is all upside (my emphasis):
To many people health checks intuitively make sense, but experience from screening programmes for individual diseases have shown that the benefits may be smaller than expected and the harms greater. One possible harm from health checks is the diagnosis and treatment of conditions that were not destined to cause symptoms or death. Their diagnosis will, therefore, be superfluous and carry the risk of unnecessary treatment.
The recommendation is best summaried by this quote (quoted in the BMJ report) from on of the authors:
“What we’re not saying is that doctors should stop carrying out tests or offering treatment when they suspect there may be a problem. But we do think that public healthcare initiatives that are systematically offering general health checks should be resisted,” said Krogsbøll.
This clarifies one possible misinterpretation of the advice. People at risk of some diseases should be investigated; but routine screening of the healthy is not justified.
Some details from the summary are quoted here:
Results were available from 14 trials, including 182,880 participants. Nine trials studied the risk of death and included 155,899 participants and 11,940 deaths. There was no effect on the risk of death, or on the risk of death due to cardiovascular diseases or cancer. We did not find an effect on the risk of illness but one trial found an increased number of people identified with high blood pressure and high cholesterol, and one trial found an increased number with chronic diseases. One trial reported the total number of new diagnoses per participant and found a 20% increase over six years compared to the control group... ...Two out of four trials found that health checks made people feel somewhat healthier, but this result is not reliable. We did not find that health checks had an effect on the number of admissions to hospital, disability, worry, the number of referrals to specialists, additional visits to the physician, or absence from work, but most of these outcomes were poorly studied. None of the trials reported on the number of follow-up tests after positive screening results, or the amount of surgery used.
The conclusion (my emphasis):
With the large number of participants and deaths included, the long follow-up periods used in the trials, and considering that death from cardiovascular diseases and cancer were not reduced, general health checks are unlikely to be beneficial.
So routine screening of healthy people doesn't seem to have any measurable benefits.
