On the face of it, Helen’s employers are looking after her well. She’s head of HR, and her package of benefits includes an annual health screen, presumably to head off any incipient problems that might affect her ability to render the company good service. She’d attended one recently, expecting to be assured she was fighting fit. Instead, she had been told it looked like she had ischaemic heart disease, and she’d been urged to see her GP.
She was keeping calm, but was understandably disconcerted. I was puzzled. In her mid-forties, she was a never-smoker, with blameless blood pressure, a healthy weight, a moderately active lifestyle and an unremarkable family history. It was difficult to conceive of a candidate less likely to develop angina, or be struck down by a heart attack.
The problem was, as part of her screening, she’d undergone a stress test. This involved her being connected to an electrocardiogram (ECG) – which records electrical activity in the heart – and then being put through progressively more strenuous exercise on a treadmill. Some way into the test, Helen’s ECG had registered changes that are associated with the heart becoming starved of oxygen. This condition is called ischaemia, and it occurs when an artery supplying the heart muscle is critically narrowed by fatty deposits known as atheroma. It is usually accompanied by chest pain or tightness. Helen assured me she had felt nothing. And, no, she never experienced such things, not even when running or doing aerobics. By now I was convinced she was in danger of becoming a victim of the health screening industry.
Stress tests, like all medical investigations, can generate “false positive” results, in which the condition tested for is mistakenly detected. Estimates vary, but it probably happens in about one out of every ten cases. That’s OK if you are performing the test to make a diagnosis. Say you have ten patients, all complaining of chest pain; a good proportion (let’s say 50 per cent) will have underlying ischaemic heart disease. When you test all ten, five will generate a true positive result but a sixth might be a false positive. So, five out of six positives reflect genuine heart trouble, meaning a positive result has an 85 per cent chance of being “right”. Not perfect, but useful when deciding who to investigate further.
But look what happens if you use the same test to screen ten healthy people like Helen, none of whom has anything wrong. You’ll get one positive result, but it will be false. Even if one of the ten symptomless people does in fact have unsuspected heart disease (and that’s a big if), you will end up with two positives, only one of which is true – so a positive result has only a 50 per cent chance of being “right”. You might as well flip a coin. To cap it all, false positives are very common in pre-menopausal women such as Helen.
Helen wasn’t to know any of this. From her perspective, she’d been to a reputable medical company, which wired her up to some impressive gadgetry that had raised grave concerns about her health. Even once I’d explained the ins and outs, a part of her mind was still thinking, “Yes, but. What if my result was true?” There are invasive investigations that could settle the question definitively but they involve exposure to radiation, or risk of stroke.
There was no way out of the conundrum created by the unethical use of a diagnostic test for screening. The private screening industry is essentially unregulated, and causes substantial worry and sometimes physical harm, all in the pursuit of profit. The same issues apply to its misuse of other diagnostic tests such as CT and MRI scans. And it’s the NHS that is left picking up the pieces when the inevitable false positives turn up.
In time, Helen regained the health confidence that her brush with the private screening industry had undermined. It will be interesting to see whether she politely declines her next invitation to be screened – or, indeed, whether her employers allow her to do so.
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This article appears in the 14 Oct 2015 issue of the New Statesman, The Corbyn supremacy