Kitabı oku: «What Doctors Don’t Tell You», sayfa 3
PART II DIAGNOSIS
2 Diagnostic Excess
Your modern-day doctor has at his disposal an array of high-tech gadgetry that allows him to monitor and measure virtually every nook and cranny of your body. He and his fellow doctors are now completely reliant upon these tests to diagnose disease. As patients, we trust tests so implicitly to provide us with a definitive view of our state of health, even to predict when we’re going to get ill at some distant point in the future, that most of our children begin having tests as soon as they’ve been conceived.
At last count, there were more than 1,400 of these, ranging from the simple blood-pressure cuff to the most sophisticated computerized nuclear magnetic imaging devices. Back in the relatively dark ages of 1987, some 19 billion tests were performed on Americans that year alone, which works out to be 80 tests for each man, woman and child.1
Despite the kind of gadgetry that would put NASA to shame, the problem is that the technology doesn’t really work very well. Most tests are grossly unreliable, giving wrong readings a good deal of the time. A false-positive test sets in motion the juggernaut of aggressive treatments at your doctor’s disposal, with all their attendant risks. But the tests themselves can be as risky as some of the most dangerous drugs and surgery, risks that are magnified because so many of these tests are patently unnecessary. In many cases (more so in the United States), doctors protect themselves against potential lawsuits by ordering every test they can. In fact, in the US, many orders for tests are motivated by a doctor’s own self-interest, since so many physicians either own or have substantial shareholdings in the facilities to which they refer their own patients.
Another problem is that, these days, technology has replaced the fine art of diagnostics – of examining a patient’s clinical history and having a good look at his eyes and the state of his tongue. The problem often comes down to trainee doctors, who often order tests under the mistaken notion that their consultant superiors desire such ‘just-in-case’ medicine. But in many cases senior doctors do flog their juniors if they fail to request particular tests, engendering the view that more is better and that massive test-taking is what constitutes good doctoring.2
Tests also make the fundamental error of assuming not only that all people are alike, but that people (and their measurements) always stay the same.
The other problem is that, unless your doctor has a particular feeling for taking apart computers in his spare time, he can get a bit muddled by this gee-whizz technology. One study found that virtually all doctors and nurses don’t know how to work a pulse oximeter, a monitoring system which is vital for monitoring patients recovering from anaesthesia and recording potential life-threatening situations.3 Consequently, they make serious errors in evaluating readings. The medics reported not being ‘particularly worried’ when patients had levels indicating that they were seriously deprived of oxygen and needed immediate attention if they were to live.4
BLOOD-PRESSURE READINGS
Your problems can start even when your doctor brandishes his blood-pressure cuff to record your blood pressure. Professor William White, chief of Hypertension and Vascular Diseases at the University of Connecticut, refers to this gizmo, known in medicalese as the ‘sphygmomanometer’, as ‘medicine’s crudest investigation’. Blood pressure, he says, can vary tremendously – as much as 30 mm Hg over the course of any day.5 In fact, the time it’s most likely to rise is in your doctor’s surgery, when you’re waiting to have the test – a phenomenon known as ‘white-coat hypertension’. A recent study comparing blood-pressure readings taken at home, at work and at the doctor’s surgery found that the most inaccurate were those performed in the doctor’s surgery.6 Such an artificially high test reading at the doctor’s surgery can launch a patient onto a lifetime of blood-pressure medication.7 The latest studies into blood pressure and hypertension have concluded that true high blood pressure is more related to average levels over 24 hours and also the degree of fluctuation between day and night than any particular or casually-made blood-pressure readings.8
These days, your doctor is more likely to give you a home-monitoring device or even to strap you up with a portable electronic device, which will measure your blood pressure at pre-set intervals over 24 hours. This is now thought to be the more accurate way of assessing your average blood pressure, although there is still a great deal of evidence that this system, called ‘ambulatory monitoring’, likewise doesn’t provide accurate enough information for doctors to decide whether a patient needs treatment for high blood pressure.9
Even the World Health Organization recommends that ambulatory monitoring is best conducted with multiple readings over six months. But because no one has yet bothered to do proper large-scale scientific studies, no one can agree over how long you should go on doing the ambulatory monitoring before making a diagnosis, or what actually constitutes high blood pressure over this period, or even how much blood pressure should be lowered by to make it ‘normal’.10
The values used today are still hypothetical, gleaned from studies of populations with normal blood pressure.11 With home-monitoring systems, accuracy also remains a large problem. Only about a fifth of self-recording devices evaluated in recent studies have met acceptable criteria.12
In the US, the Food and Drug Administration mandates that any hypertension medication must be shown to lower blood pressure over 24 hours through ambulatory monitoring. Nevertheless, neither doctors nor drug companies really understand which reading – morning average, evening average, ambulatory reading, difference between day and night, degree of variation – shows that things are finally under control. Furthermore, many patients have different degrees of variability, depending on the nature of the stress they confront on the job.13 Older patients also have more exaggerated differences in day and night readings – the significance of which is anyone’s guess.14
A task force of participants at the 1999 Consensus Conference on ABP monitoring, sponsored by the International Society of Hypertension, recommended against using ambulatory monitoring for routine screening purposes.15 The latest recommendations are that patients use ambulatory monitoring for initial diagnoses of hypertension, and self-monitoring for long-term follow-up.16
Even the variation between the arms influences a blood-pressure reading. One doctor from City General Hospital in Staffordshire, England discovered a variation of more than 8 mm Hg in systolic blood pressure between the two arms of nearly a quarter of his patients. In one case, the difference was 20 mm Hg.17
Things are just as confusing for pregnant women and children. Doctors and health-care workers can’t even agree over how to record the second beat of blood pressure (called the diastole), which measures when blood fills up the heart,18 or whether certain sounds accurately reflect diastolic pressure. This was even the subject of a heated debate at a world congress of hypertension in pregnancy in Italy, calling for an ‘international consensus’ on how to record blood pressure in pregnant women. In fact, some researchers have claimed that doctors have been using the wrong type of blood-pressure test on pregnant women: obstetricians and midwives prefer the blood-pressure gauge called Korotkoff phase 4, but research shows that phase 5 testing is far more reliable – the reverse of the prevailing view. In one test, virtually nobody agreed on the reading from a K4 test, while everyone was in agreement on the K5 test.19 As for children, the latest recommendations are that they, too, have ambulatory monitoring.20
This potential for different interpretations in readings can cause problems for you if your blood pressure is being monitored by several people who may have had different training in how to read the cuffs.
CHOLESTEROL TESTS
Today, a cholesterol test is the most-often sought diagnostic test of all. In a general check-up a doctor will routinely offer you one to determine whether if you are at risk of heart disease. The test measures the amount of cholesterol and triglycerides in the serum (the non-cellular part) of your blood.
A total cholesterol test, which is rarely used these days, will examine all the blood fats, including the overall cholesterol level, the LDL (low-density lipoproteins, or ‘bad’ cholesterol), HDL (high-density lipoproteins, or ‘good’ cholesterol), VLDL (very low-density lipoproteins), chylomicrons (fats that are present right after a meal but ordinarily disappear within two hours) and triglycerides (compounds in the body that shift fatty acids through your blood). However, the typical cholesterol test only examines the LDL cholesterol.
The test requires a relatively straightforward blood test. You are asked to fast for 9–12 hours before the test is taken. A tourniquet is applied to your arm, so that the lower veins will pool with blood, and the blood is drawn from a vein either on the inside of the elbow or the back of the hand.
All fat tests (lipids, as they are known in medicalspeak) are measured in terms of milligrams per deciliter of blood (mg/dL). Medicine rates as acceptable a total cholesterol count of less than 200 mg/dL. The current medical wisdom is that the higher the cholesterol count, the greater the risk of heart disease or atherosclerosis (clogged arteries), and that if your levels are over 240 mg/dL you nearly double your risk of heart disease, compared with someone in the normal range.
The (largely unsubstantiated view) is that high LDL cholesterol levels may be the best predictor of risk of heart disease; if you have no other risk factors, your LDL count should come in at below 160 mg/dL. People with diabetes, heart or vascular disease, other risk factors or a family history of heart disease should try to keep their cholesterol levels even lower, say doctors.
Medicine loves statistics, and nowhere is this more evident than with this test, where a high LDL is thought to be countered by a high HDL, and vice versa. HDL cholesterol levels of 60 mg/dL are thought to counteract other risk factors; HDL levels below 40 mg/dL themselves become a risk factor.
Even if you have low LDL and high HDL cholesterol, high triglyceride levels may put you at risk. For instance, a normal triglyceride level should be less than 150 mg/dL. A vast array of conditions can result in an inaccurate test – liver disease, an underactive or overactive thyroid, kidney problems, liver disease, malabsorption of your food (say from a leaky intestinal tract), pernicious anaemia, infection and diabetes that isn’t under control. Pregnant women and those who have had their ovaries removed also will register high on the test. An array of prescription drugs – beta-blockers, thiazide diuretics, steroids, phenytoin, sulphonamides, the Pill, even vitamin D – can also throw off your test.
The other problem is the inherent inaccuracy of the lab test itself. According to one study, some 70 per cent of samples analysed have evidence of bias in the computation of results21; other research shows the products themselves used to measure blood cholesterol have major drawbacks.22 In one Canadian study of total cholesterol tests, nearly one-quarter were misclassified (as, say high risk), nearly a fifth registered a false-positive (a high cholesterol level when it wasn’t) and among those in the ‘high risk’ category, half had a false-positive reading.23
A few people in medicine are waking up to the fact that LDL levels alone are not an accurate predictor of heart disease. A large British Health Survey for England found that forecasting heart disease was far more accurate when factoring in the HDL levels, too.24
ECG Readings
Besides blood-pressure and cholesterol measurements, your doctor’s next favourite activity is listening to the state of your heartbeat. However, these days, the all-purpose stethoscope (never proved to have any advantages over the naked ear) has been replaced by a number of space-age gadgets, all designed to record the most minute changes in your heart’s ability to do its job.25 The stalwart of any cardiac specialist is the electrocardiogram (ECG), even though studies demonstrate enormous potential for error in recording or interpreting correct results. One study showed that computers, often used to interpret ECG readings, were only right two-thirds of the time, and missed 15 per cent of cases of enlargement of the right ventricle. Nevertheless, human beings didn’t fare much better; even trained heart specialists misinterpreted one out of every four readings.26 This is largely because, as with blood-pressure, readings can be affected as much as 20 per cent by recent activity, time of day, and even factors such as fear of the cardiologist’s findings! The late Dr Robert Mendelsohn wrote of a study in which electrocardiography detected only a quarter of proven cases of heart attack, and another study in which the tests found gross abnormalities in more than half of perfectly healthy people.27 As Stephen Fulder, author of How to Be a Healthy Patient (Hodder & Stoughton), notes, an incorrect ECG has led to ‘vague diagnoses of organic brain disease in healthy but unruly children, turning them into medical cases’.28
More state-of-the-art these days than the ECG is echo-cardiography – a diagnostic test on the heart, often using a mixture of contrast agents and soundwaves. The procedure had been gaining acceptance for its safety and accuracy. However, as with much ‘perfectly safe’ new technology, doctors have only recently realized that it is more dangerous than had been thought, possibly leading to life-and-death complications.
The first major study into the procedure discovered that it can be life-threatening in one in 210 cases, requiring special treatment or a stay in hospital; two people of the 3,000 studied suffered a heart attack after the procedure had been completed.29
The procedure often employs the use of microbubbles of a contrast agent like octafluoropropane, which are useful in visualizing the tiniest blood vessels of the heart. In laboratory research, rats have developed cardiac arrhythmias after being exposed to echocardiography because the contrast agent interacted with ultrasound, causing the alterations in heart rhythms. Although animal models often don’t apply to humans, this effect on a living being demonstrates that pulsed ultrasound can interact with bubbling contrast agents.30 There’s also evidence that the microbubbles cause destruction of capillaries, leaking red blood cells into skeletal muscle.31 Furthermore, the act of using pulse-sound waves with contrast agents in the brain has been shown to cause tissue damage to vascular walls, causing haemorrhage and tissue death.32
ANGIOGRAPHY
If your doctor suspects that something is awry, he may trot you off for angiography, an x-ray test supposed to examine the state of your arteries via a contrast dye. The doctor will place a catheter into a blood vessel in your arm or leg, guide it towards the heart, and inject what is usually an iodinated dye like isosorbide dinitrate, which then travels into the main pump of the heart. Once all this is in place, the doctor will then snap pictures of your heart from different angles, all the while replenishing the supply of dye.
There’s plenty of evidence that this test also has a poor batting average, wrongfully setting in motion one of a number of potentially lethal heart operations. In one test in Boston, half of the 171 patients recommended to have a coronary angioplasty (the operation where furred-up veins are opened by tiny inflated balloons) on the basis of their angiograph were found not to need the operation. In the end, only 4 per cent of the patients advised to have the angiograph really needed one.33
Angiographs are also especially open to misinterpretation. In another study in which the pathology reports of deceased patients were compared with prior angiographs, two-thirds were found to be wrong.34 A number of critics blame the test itself, which only examines the main coronary arteries, will not show any vessel smaller than a 0.5 mm in diameter and will only highlight, at best, a quarter of all the blood flowing to the heart.
Many patients with an abnormal angiogram are referred for surgery, when, at best, the procedure can locate the site of a block and its severity, but not overall heart function. Angiography, for instance, cannot distinguish between patients with stable and unstable angina.
There’s also a problem with accuracy. In one instance, after the deaths of three patients unsuccessfully treated by angioplasty, pathology reports found that the angiography on which the procedure was recommended had given misleading information about the patients’ conditions.35
Finally, this nasty little test is not without its own dangers. The procedure itself causes death in two of every 1,000 patients or, at very least, can trigger a heart attack, stroke or severe blood loss.
Serious side-effects occur, regardless of the type of dye used,36 and reactions to the dye often appear up to a week later. In one study, nearly half the patients involved complained of delayed reactions – including itchiness, rash and nausea – from one hour to seven days later.37 More than 5 per cent of patients suffer reactions to the dye of moderate intensity, particularly those who have had the test before,38 and one in ten will have a reaction of some sort. Although most are mild, at least 1 in every 2,500 is quite severe.39
If you have to have such a test, the less dangerous option may be magnetic-resonance-imaging angiography, which doesn’t require either x-rays or dyes, but a magnetic field and pulses of radiowave energy to produce pictures of soft body tissues.40 And as it provides pictures in three dimensions and on multiple planes, it shows better differentiation of tissues.
X-RAYS
X-rays are the most common procedure you’re likely to be exposed to at least once in your lifetime. Today they represent approximately 10 per cent of any Western nation’s health expenditure. Ionizing radiation is actually comprised of very high-frequency waves, which pass through living tissue. Depending on how dense the tissues are, the body retains some of this radiation. These absorbed rays are what gets recorded on the film as white or grey; those that pass completely through hit a plate of photographic film and show up as dark grey or black. Besides mammograms, bone x-rays and dental x-rays, the newest kind of x-rays include CAT scans, in which a moving beam of x-rays creates a three-dimensional picture, usually of the brain, and fluoroscopy, which sends the x-ray shadow picture onto a television screen. Occasionally contrast dyes like iopamidol or mediums like barium are used to provide a clearer picture.
Although the newest equipment uses lower and more precisely targeted doses, there is still no such thing as a safe x-ray (that goes for dental x-rays, too). In all of medicine there is virtually no disagreement that ionizing radiation is damaging – and those risks are multiplying as our understanding of the medium grows. ‘Medical irradiation is by far the largest man-made contribution to the radiation burden of the population of developed countries,’ R. Wootton, professor and director of Medical Physics at Hammersmith Hospital in London, wrote in a textbook on the subject. In the UK, he says, x-rays ordered by doctors account for over 90 per cent of the total radiation exposure of our population.41
X-rays harm people in three ways. First, they can damage individual cells (although the harm caused by the lower doses is usually quickly repaired). Rarely (but depending on exposure), this damage can convert the cell to a cancer cell. Although we don’t know exactly how this works, it has been proposed that, since a cell is 75 per cent water, most of the radiation will be absorbed by the water, forming free radicals, which are known to be carcinogenic.42
Second, if a woman is pregnant, it can injure the developing foetus, causing death or malformations.
Finally, x-rays can damage the sperm or ovaries of children or adults, causing abnormalities in future generations. We also know that x-ray exposure is cumulative; the danger of something going wrong may increase every time you get another one.
We’re still coming to grips with exactly how dangerous x-rays are, however. Unnecessary radiation from x-rays may be responsible for 700 cancer deaths in the UK every year, and perhaps 5,700 cancer deaths per year in the US, according to a recent Oxford University study.43 But these figures may still be conservative. A UK National Academy of Science committee reviewed the usual assumptions that x-rays were responsible for 1 per cent of all leukaemias and 1 to 2 per cent of all other cancers, and concluded that the real risk could be as much as four times higher44 – a conclusion also reached that same year by the International Commission on Radiological Protection.45 Recently, multiple x-rays have even been linked with multiple myeloma – a form of bone cancer now sharply on the rise. Those who’d had the most exposure had a four times increased risk, the National Cancer Institute found.46
As far back as the 1950s, medicine discovered a link between leukaemia and prenatal x-rays. X-raying pregnant woman used to be routine, on the ludicrous notion that x-rays could tell a doctor whether her pelvis was ‘wide enough’ for the foetus to fit through during birth. We now know that if children are exposed to x-rays in utero their risk of all cancers is increased by 40 per cent, of leukaemias by 70 per cent, and of tumours of the nervous system by 50 per cent.47 There also may not be a safe ‘dose threshold’; single babies who’d received five to six times less radiation than twins who’d been x-rayed more frequently had the same incidence of cancer.48 To put these numbers in perspective, for every million babies exposed in the womb to even a single rad of x-rays – the equivalent of a single picture of the stomach and intestines – between 600 and 6,000 could develop leukaemia.49 John Gofman, Professor of Molecular and Cell Biology at the University of California, believes that women who undergo yearly mammograms receive cumulative doses not unlike the Japanese atomic bomb survivors.50
Gofman estimates that women’s breasts receive 0.4 rad of medical x-rays a year for each year of life. If you compare that dosage with the levels suffered by Japanese atomic bomb survivors, he says, 114,000 women, from 62 to 75 per cent of those diagnosed every year with breast cancer, could blame x-rays as the cause. Besides cancer and genetic deformities, x-rays of the brain can lead to abnormal hormonal function, possibly causing underactive thyroid and infertility, or resulting in subtle changes in your adrenal glands.51 The US Food and Drug Administration has also lately received a number of reports of patients suffering skin burns after radiation, so severe in some instances that the skin has died. The problem is complicated by the fact that these injuries don’t show up for weeks after exposure. Your typical dose of fluoroscopy can result in skin injury after less than an hour.52
Even the offspring of those exposed to x-rays suffer. Exposure to x-rays increases a woman’s risk of giving birth to a Down’s syndrome baby.53
Although x-ray risk is cumulative over a lifetime of exposure, even single shots are not innocuous. According to the United States’ Health Research Group, a consumer group which reports on risks in medicine, topping the list are x-rays of the upper intestine, which give an equivalent dose to the entire body of 400–800 millirads; the next highest (apart from the risk associated with x-raying the other organs) is the spine (100–500 millirads); stomach, breast and pelvis (100–200 each); skull or shoulder (25–75); chest (20–60); with whole mouth dental x-rays taking up the rear at 10–30 millirads.54
In case you are feeling complacent about that low dosage from dental x-rays, a single bite-wing dental x-ray is equivalent to smoking half a cigarette every day for a year. The US Academy of Sciences figures that one barium meal shot of the intestines carries the same risk as smoking up to a pack of cigarettes a day for a year. This means that, with x-rays of the lower back, which some 700,000 people undergo in Britain alone every year, 19 people could die each year as a direct result.55
Even if everyone in medicine knows that x-rays are dangerous – possibly dazzled by another of their ‘miracles’, the ability to ‘see’ through living tissue, Superman style – doctors blithely downplay the dangers and make few efforts to minimize exposure when ordering up a set, even on your teeth. Most GPs and orthopaedists have a kneejerk approach to ordering x-rays.
A joint working party established between the UK’s Royal College of Radiologists and National Radiological Protection Board (NRPB) reviewed the existing evidence in 1990 and estimated that up to one fifth of the x-ray exams done in the UK were unnecessary or downright useless.56 In one examination of patients given x-rays of the lower back, more than half were absolutely unnecessary57 In the US, the Food and Drug Administration reckons that a third of all radiation is unnecessary.58
The most common unnecessary x-rays are those of the chest, limbs and joints. This translates into some seven million unnecessary x-ray exams in a single year. The UK’s more modest wastefulness has worrying implications for the rest of the West, since the UK performs only about half the number of x-rays per person as other countries such as France or the US,59 where seven out of every 10 people get subjected to at least one x-ray every year.60 In Canada the figures are even worse: virtually everyone gets an annual x-ray of some sort.61 (It’s also no cause for complacency in the UK, since British doctors order twice the number of certain types of x-rays – barium meal and enema – as their American counterparts.62) The NRPB has recently announced that overall radiation in the UK could be halved without reducing diagnostic effectiveness.
For instance, doctors routinely x-ray for back pain, when it has never been found to do any good at all.63 Skull x-rays have a poor batting average in detecting bleeding in the brain,64 and even the good old chest x-ray, used to detect tuberculosis, is considered a waste of time by the World Health Organization.65 The prestigious medical journal The Lancet admitted that most chest x-rays routinely performed on patients awaiting surgery other than on their heart or lungs were of so little benefit that over a million pounds’ worth of x-rays would have to be done to end up saving a single life.66
The decision of whether you need an x-ray or not also depends on the whim of the individual doctor. An audit of nearly a million day and in-hospital patients has shown that referrals for x-ray varied by 13-fold in general and up to 25-fold for chest x-rays, depending on which consultant was in charge.67
Because the reproductive organs are susceptible to radiation damage, they should always be protected from exposure during x-ray by a lead shield. Nevertheless, in a Consumers’ Association (Which?) report, in 40 per cent of cases the men surveyed had not had their testes shielded, and women were unprotected two-thirds of the time.68 (In a third of cases, no attempt was made to find out if the women were pregnant.) In another study of children, three-quarters of the time the lead shields used to protect the reproductive organs hadn’t been used or placed properly.69
Obviously there are times when x-rays are invaluable – particularly when limbs are first broken (though many doctors insist on constant new shots to check the progress of healing). However, even if your doctor is responsible about ‘dose constraints’ – the new buzzword among radiologists for the least amount of radiation necessary for individual snapshots – you still could be getting more radiation than necessary, largely from ageing equipment. The NRPB has reported that patients in some hospitals receive doses 20 to 30 times higher than necessary for obtaining diagnosis from machines that were, in some cases, 15 years old.70 Just a few years ago Liz Francis, NRPB information officer, said ‘physicists were saying that old x-ray equipment was giving out doses bigger than Chernobyl’.71
Even dental x-rays can subject you to unnecessary risks, since they are often performed by untrained staff who can’t use the equipment properly and who may either need to repeat the exercise or will set the dosage unnecessarily high. Two dentists in the West Midlands escaped suspension by their professional body for using untrained school-leavers to take their x-rays when it became clear that dentists throughout Britain were doing exactly the same thing.
As with most tests, there is a strong likelihood of human error in interpreting the results. One study of Harvard radiologists found they disagreed on the interpretation of chest x-rays half of the time. There were significant errors in 41 per cent of their reports.72
Ücretsiz ön izlemeyi tamamladınız.
