
There are a number of instances when we ought to have tests. Just thinking about blood tests to start with, I tend to order these for a whole host of symptoms that people might come in with – tiredness, abdominal pain, joint pains, itching being just a few. In these cases the blood test is to help me make a diagnosis. Is the itching because of anaemia? Is this person tired because their thyroid is underactive? Are these joint pains because of an autoimmune disease like rheumatoid arthritis or lupus? X-rays and scans can also help to make a diagnosis. If I’m thinking about a long term cough possibly being TB I would ask for a chest x-ray and if a female patient was suffering from very heavy periods I would usually ask for a pelvic ultrasound scan. This is all fairly straightforward.
Blood tests are also essential in keeping track of how certain conditions are being managed. Diabetes is a perfect example here. HbA1c, cholesterol and other lipids and kidney function are all very necessary tests which must be done regularly.
There are a number of important aspects of tests in general which must be borne in mind. Firstly, hardly any test is 100% accurate. People often think that a scan or a blood test is like a magic eye or marker which will give doctors a quick answer, but this is often not the case. For instance, the number of times I have had to recheck a blood test where a potassium level has come back high or not been run because it had ‘haemolysed’ (disintegrated) are too frustrating for both me and the patient to recount! And as for scans and x-rays, they often come back reported normal yet the person still has a symptom. Keeping on the accuracy theme, I have sent several patients to my local hospital outpatients with chest pain over the years which I thought was stable angina (chest pain on exertion arising from the heart). Many were sent back to me with reassurance from the heart specialists that their ‘exercise test’ (a gold standard test which elicits whether the pain is from the heart) was negative – i.e. the test suggested they didn't have heart disease. Some of these patients went on to have a heart attack within the following few weeks. So much for a negative exercise test being reassuring! This particular test will thankfully soon be out-phased by 64 slice CT which shows a graphic picture of any blockages in the heart’s blood vessels.
The reason for this is that often the best test available isn’t good enough. We know that there is a national screening programme for cervical and bowel cancer, but ovarian cancer and prostate cancer are still not screened for. Why? Because the tests for them are simply not accurate enough.
Then there is the rationale of whether to carry out a test at all. Some say that a really good doctor knows when not to order a test and that no test should be seen as ‘routine’. For instance, I would say that most doctors would not perform blood tests or x-rays on children unless really necessary. One of the reasons for this is that no-one wants to put a needle into a child for no reason. In addition to this, x-rays expose us to radiation and it seems unacceptable to do that to a child unless it was absolutely necessary. One study showed that 0.6% of all cancers in the UK are due to having x-rays (and CT scans) taken. A CT scan of the chest or abdomen gives you the equivalent of a few years of ‘background’ radiation which is what you’d normally be exposed to in the environment, whereas a chest x-ray gives you a few days worth. All this is worth thinking about when asking your doctor to send you for that x-ray again. (Nitpickers may like to know that x-rays should actually be called radiographs, but it's such a mouthful)!
I often get asked about health screening and whether it is worth having a whole body MRI or other screening scans or private healthcheck. Most of us have seen advertisements or received mailshots about this type of thing and many of my patients do go and have a watered down version of this. It’s often called a health screen or wellness check. I don’t think that there is anything wrong with having these tests although the number of times some companies will take your money and send you back to your own GP when they pick up an abnormality irritates me. Here’s my advice. If it’s a simple check up where you are being offered a basic cholesterol check, ECG, blood pressure, weight, height, examination then save your money and please ask your GP to do this.
When it comes to scans of body parts, you can’t simply ask your GP for these without good reason as the NHS is firmly based on need, so if you haven’t got any symptoms or exceptionally strong family history you won’t get a scan from your GP. No way. If you do decide to go privately to get screened via MRI scans, very rarely do they reveal anything sinister in the absence of symptoms. So it comes down to your own level of anxiety at the end of the day. But how often do you go back for another scan? Every month? Every year? That’s the trouble – once you start it’s hard to stop. The other side is that some conditions have no symptoms at all in the very early stages and screening could potentially identify the disease before it’s too advanced.
Comparing our neighbours across the pond in the USA, they run a private health care system, which means they tend to do a lot more tests as the insurance companies pick up the tab, so there is money to be made by doctors and hospitals from “getting a brain scan even though the headache is mild – just to be on the safe side…” (Of course if you have no insurance you get very different care, if any).
Tests in medicine, then, are important but they are almost never 100% accurate. The bottom line is that they need to be done for a good reason and need to be interpreted carefully so please remember that next time you and your doctor discuss whether to perform one.



















