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.
