YOUR HEALTH Dr James Le Fanu: 25 October
The technology of chemical analysis is now so sensitive it is possible to detect hormones and enzymes circulating in the bloodstream at such concentrations equivalent to an aspirin in an Olympic-sized swimming pool. But technology is never faultless and it is no surprise that blood tests may indicate there is something wrong when there is not (false positive) or, conversely, they can be ‘normal’ even when there are strong reasons for supposing there is something amiss (false negative).
We start with the false positive. Several factors, including exposure to infections (even keeping pets) can stimulate production of antibody chemicals in the blood that mimic the substance being measured, so its concentration in the blood will seem higher than it is. This has proved a problem in patients with severe chest pain suggestive of a heart attack, apparently confirmed by tests measuring an enzyme released by damaged heart muscles. The appropriate treatment is initiated but further investigations, including X-raying the arteries to the heart, reveal there is no evidence of a coronary at all.
The false negative has proved particularly troublesome in those who have all the symptoms of an underactive thyroid (or hypothyroidism), such as weight gain, sensitivity to the cold, poor concentration, fatigue and so on. But perplexingly, the thyroidfunction tests are normal and the dramatic improvement that comes with thyroxine treatment is thus denied.
This is not unusual as there are accounts of people who battle for years with intransigent doctors, only to have their lives transformed when they finally find a GP willing to prescribe the appropriate treatment. In a further twist, those with persistent symptoms, despite being treated, request they take a higher dose but this too may be denied as relevant blood tests are reputedly ‘back to normal’.
Blood tests have become such a ubiquitous feature of medical practice that their interpretation can a ffect many people’s lives. It is all the more important to recognise that while being scientific and objective they involve measuring a single chemical in very small concentrations at one moment in time. This is not a sound basis for making decisions without taking into account the ‘whole picture’.
This week’s medical query comes courtesy of a woman from Su ffolk concussed after a fall on black ice three years ago. She experienced the typical symptoms of ‘postconcussion syndrome’: severe headaches, sensitivity to light and noise, diffculty in walking in a straight line and disorientation. This gradually improved over a period of five weeks but she now finds that even modest exertion, such as shopping or travelling by bus, prompts a recurrence.
‘The only thing I can do is go to bed in a darkened room, take painkillers and wait until the symptoms have gone,’ she writes.
There is regrettably no treatment for post-concussion syndrome as its precise cause remains unknown. The combination of headaches and sensitivity to light is, however, strongly suggestive of migraine, to which this type of injury, it is claimed, may predispose. It would be worthwhile trying a course of preventive anti-migraine medication to see whether this improves matters.
Email drjames@lady.co.uk
We start with the false positive. Several factors, including exposure to infections (even keeping pets) can stimulate production of antibody chemicals in the blood that mimic the substance being measured, so its concentration in the blood will seem higher than it is. This has proved a problem in patients with severe chest pain suggestive of a heart attack, apparently confirmed by tests measuring an enzyme released by damaged heart muscles. The appropriate treatment is initiated but further investigations, including X-raying the arteries to the heart, reveal there is no evidence of a coronary at all.
The false negative has proved particularly troublesome in those who have all the symptoms of an underactive thyroid (or hypothyroidism), such as weight gain, sensitivity to the cold, poor concentration, fatigue and so on. But perplexingly, the thyroidfunction tests are normal and the dramatic improvement that comes with thyroxine treatment is thus denied.
This is not unusual as there are accounts of people who battle for years with intransigent doctors, only to have their lives transformed when they finally find a GP willing to prescribe the appropriate treatment. In a further twist, those with persistent symptoms, despite being treated, request they take a higher dose but this too may be denied as relevant blood tests are reputedly ‘back to normal’.
Blood tests have become such a ubiquitous feature of medical practice that their interpretation can a ffect many people’s lives. It is all the more important to recognise that while being scientific and objective they involve measuring a single chemical in very small concentrations at one moment in time. This is not a sound basis for making decisions without taking into account the ‘whole picture’.
This week’s medical query comes courtesy of a woman from Su ffolk concussed after a fall on black ice three years ago. She experienced the typical symptoms of ‘postconcussion syndrome’: severe headaches, sensitivity to light and noise, diffculty in walking in a straight line and disorientation. This gradually improved over a period of five weeks but she now finds that even modest exertion, such as shopping or travelling by bus, prompts a recurrence.
‘The only thing I can do is go to bed in a darkened room, take painkillers and wait until the symptoms have gone,’ she writes.
There is regrettably no treatment for post-concussion syndrome as its precise cause remains unknown. The combination of headaches and sensitivity to light is, however, strongly suggestive of migraine, to which this type of injury, it is claimed, may predispose. It would be worthwhile trying a course of preventive anti-migraine medication to see whether this improves matters.
Email drjames@lady.co.uk