When someone comes to see you with a worry about their health, it helps if you can guess what they would like you to do. Often, they’re hoping that you’ll send them for a test. Or even several tests. By “tests”, people rarely mean the simple investigations you can do in clinic: blood sugar levels, oxygen saturations, a urine dipstick. These never seem to inspire as much confidence as X-rays or blood tests, or anything involving a consent form. While many people hate hospitals – anxiety, fuss, too hot, too busy – some greet the prospect of an X-ray with beaming relief. Nothing could be more popular – except for a CT scan. You can almost see people thinking: “At last – answers! Results!” There is no doubt medical investigations are potentially invaluable. So why are we always withholding them, a patient with backache asked me. Why not do some tests, if we have so many available?

No medical system in the world is more committed to testing than America’s (because nowhere in the world is more litigious). But recently The American Board of Internal Medicine Foundation issued a list of 45 investigations it considered unnecessary. It states, very clearly: do not do ECGs on patients unless they have chest pain or significant risk factors for heart disease; do not perform MRI or CT scans on patients with straightforward back pain; do not do CT scans on patients with uncomplicated headaches, or on patients who have had a single black-out, or faint; and not everyone needs a chest X-ray before they have an operation.

All of these are already best medical practice in the UK, but it is odd and momentarily counter-intuitive to see a list of do nots so clearly spelled out. The temptation is to ask, why not? Surely 46 tests will find 46 problems which medicine can go on and solve?