Diagnosing hypertension
| January 1, 2007
In-Depth Report
Diagnosing hypertension
As experts have learned more about the causes and consequences of hypertension, their approach to diagnosing it has changed. Since the 1990s, doctors have come to regard systolic hypertension as more significant than previously thought.
Although both systolic and diastolic blood pressures tend to rise and fall together, especially in young and middle-aged adults, diastolic pressure fluctuates less. For this reason, doctors have traditionally focused on the diastolic reading. However, in 2003, the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC) published a new classification of blood pressure for adults that states unequivocally that in people over 50, a systolic reading of more than 140 mm Hg is a much more significant factor in cardiovascular disease than the diastolic reading. This was based on a preponderance of research evidence highlighting the significance of systolic pressure. For example, the Framingham Heart Study showed that systolic blood pressure alone correctly identified 91% of those who needed treatment, while high diastolic pressure identified only 22% of individuals needing treatment. In addition, the Systolic Hypertension in the Elderly Program, or SHEP, trial found that drug treatment for high systolic pressure significantly reduced the risk of stroke by 36% and cut heart attack and heart failure rates. In light of these findings, the JNC recommends the following:
No matter what your age, strive to reduce systolic blood pressure to less than 140 mm Hg.
Systolic blood pressure should become the principal focus for the detection, evaluation, and treatment of hypertension, especially in middle-aged and older Americans.
Age-adjusted blood pressure targets are inappropriate. For instance, the general rule that it's acceptable for your systolic blood pressure to be 100 plus your age is incorrect.
Testing for hypertension
To determine whether you have hypertension, a medical professional will take a blood pressure reading. To prevent a false high reading, avoid caffeine, exercise, or smoking for at least 30 minutes and rest quietly for at least 5 minutes beforehand.
A diagnosis of hypertension is seldom based on a single reading, because blood pressure varies throughout the day. So your doctor will want to confirm high measurements on at least two occasions, usually within a few weeks of one another. The exception to this rule is a blood pressure of 180/110 mm Hg or higher, especially if there are symptoms of an underlying disease. A reading this high calls for prompt treatment.
In general, blood pressures between 160/100 and 179/109 mm Hg should be rechecked within two weeks, while measurements between 140/90 and 159/99 should be repeated within four weeks. People in the prehypertensive category (between 120/80 and 139/89 mm Hg) should be rechecked within four to six months, and those with a normal reading (less than 120/80 mm Hg) should be rechecked annually. However, your doctor may schedule a follow-up visit sooner if your previous blood pressure measurements were considerably lower, signs of target-organ damage are present, or you have other cardiovascular risk factors. Also, most doctors routinely check your blood pressure whenever you go in for an office visit.
Gathering more data
After a high initial reading, it's often beneficial to have one or more measurements done outside the doctor's office before returning for the follow-up visit. This information can help your doctor distinguish between sustained and white-coat hypertension. Home monitoring can aid in the diagnosis, and doctors often suggest that hypertensive patients learn to monitor their pressure at home.
Once a diagnosis of hypertension is confirmed, the next step is to determine whether target-organ damage has occurred and to rule out any disorder that could be to blame for your high blood pressure (see "Secondary hypertension"). Expect to undergo a thorough evaluation, including a medical history, physical examination, laboratory tests, and possibly other diagnostic exams such as a chest x-ray, echocardiogram, or exercise stress test. Mention any recent changes in weight, physical activity, alcohol consumption, or tobacco use. Also, list all the prescription and over-the-counter medications, herbal products, and even any illegal drugs you're taking or have recently taken. Some of the substances found in these products can raise blood pressure or interfere with blood pressure medication.
Helpful medical tests
Routine urine and blood analyses can reveal medical conditions. For instance, protein or blood in the urine may be a sign of kidney damage, while glucose suggests diabetes. Blood tests typically measure sodium, potassium, chloride, calcium, bicarbonate, glucose, and cholesterol, as well as urea nitrogen or creatinine, which are indicators of kidney function. If your doctor suspects that you have another condition or target-organ damage, he or she may order further tests.
An electrocardiogram (EKG or ECG), which measures electrical activity of the heart and gives a general picture of the heart's health, is especially important. The initial EKG is called a baseline. Later EKGs can be compared with the original to reveal changes that may indicate coronary artery disease or thickening of the heart wall.
An exercise stress test assesses how your cardiovascular system responds to physical activity. If you have high blood pressure, this information is sometimes important to know before you start an exercise program. The test monitors the electrical activity of your heart and your blood pressure during exercise, which usually involves pedaling a stationary bike or walking on a treadmill. Stress tests can reveal problems that aren't apparent when you're at rest. In many circumstances, imaging scans of the heart's blood supply are done during stress testing.
Chest pain, dizzy spells, palpitations, or other symptoms may indicate heart disease, which calls for additional testing. For instance, your physician may order Holter monitoring, in which you wear a portable device that takes a continuous EKG recording for 24 hours or longer. Another test is the echocardiogram, which uses ultrasound waves to show your heart in motion. It's used to diagnose thickening of the heart wall, valve defects, blood clots, and excessive fluid around the heart.
Symptoms such as urinary tract infections, frequent urination, or pain in your flank (low down on the side of your abdomen) may be signs of a kidney disorder. If the doctor hears a bruit — the sound of a rush of blood — through a stethoscope placed on the flank, it may be a sign of renal artery stenosis, a narrowing of an artery supplying the kidney. You may have to undergo blood analyses and imaging tests to learn whether a kidney problem is causing your hypertension.
A better way of measuring hypertension?Blood pressure is a numbers game, and the rules keep changing. Some experts suggest that the most accurate predictor of heart disease risk may be the difference between your systolic and diastolic blood pressure. This third number is called pulse pressure. Some research suggests that pulse pressure might be an important number. In a 1999 issue of the journal Circulation, researchers used data collected from the Framingham Heart Study to investigate whether pulse pressure was more useful in predicting heart disease than either systolic pressure or diastolic pressure alone. They calculated the risk of cardiovascular disease for each additional 10 mm Hg in pulse pressure, systolic pressure, and diastolic pressure. For pulse pressure, each additional 10 mm Hg correlated with a 23% increase in risk. By comparison, each 10 mm Hg rise in systolic pressure was associated with a 16% greater risk, and an equivalent increase in diastolic pressure was linked to a 14% increase in risk. That pulse pressure might be illuminating makes sense. Each time a heartbeat causes blood to surge, healthy blood vessels, which are elastic, give a little. This elasticity translates into a spread of 40–50 mm Hg between systolic pressure (when the blood is pushing hardest on the artery walls) and diastolic pressure (when the heart is relaxed and is not pushing blood through the arteries). If the arteries are thick and stiff, the gap between systolic and diastolic pressure widens. Systolic pressure goes up because the arteries have lost their elasticity and the heart must push harder to force blood through. The diastolic pressure decreases because the stiffened arteries don't return to their original size as easily between heartbeats. A systolic-diastolic difference of up to 50 mm Hg is fairly normal. But a difference of 60 mm Hg or more is high and may concern some doctors. However, it isn't clear that hypertension treatment using pulse pressure as a guide would produce any better results than treatment using the conventional guidelines. And after all, health outcomes are what really matter. So although pulse pressure is an active topic among hypertension researchers, there's no reason to become overly concerned about it just yet. |
Monitoring blood pressure at home
Stress, exercise, and even a few drinks the night before your doctor's appointment can push your blood pressure up. So it's often difficult to tell whether an unusually high reading at the doctor's office means you have hypertension — or, if you already have high blood pressure, that it's worsening — or if that work deadline has temporarily inflated your numbers.
To offset this problem, many doctors encourage people to monitor blood pressure on their own. Home monitoring is especially useful for people with white-coat hypertension or labile hypertension, as well as to track responses to exercise, medications, or changes in treatment.
Most pharmacies have machines that customers can use free of charge, but a home monitor is more practical for taking daily readings. It's possible to spend as much as $70–$100 for a sleek machine with extra features you may not need, but if all you want is to track your blood pressure, most drugstores stock a basic unit for less. Your doctor may be able to lend you a blood pressure monitoring unit temporarily. If you need to purchase the equipment for long-term use, your insurance plan may cover the expense.
Home-testing kits
Manual blood pressure kits, some of which include a stethoscope, are similar to those used by health care professionals. Manual blood pressure models are the least expensive and the most accurate devices for home monitoring. However, they have their drawbacks. You must wrap the cuff around your arm, pump it up, and listen through the stethoscope while simultaneously turning a valve to deflate the cuff and watching the needle gauge. People with average manual dexterity, eyesight, and hearing often master this procedure easily, but if you are hampered by arthritis, vision problems, or hearing loss, you may need someone to assist you. Or you may be better off with an electronic monitor.
Electronic monitors, which measure your blood pressure without the use of a stethoscope and display your blood pressure readings digitally, are easy to handle alone, making them worth the extra cost for some people. You can choose among models with a manual arm cuff (which you inflate yourself by squeezing a rubber bulb), an automatic arm cuff (which you inflate with a touch of a button), or an automatic wrist cuff. Consumer Reports tested several brands, and the wrist cuff models scored high marks for convenience but lower ratings for consistent readings. Those with arm cuffs received the highest ratings for accuracy. Electronic monitors have various features, such as memory recall of previous blood pressure measurements. The designs also vary in ease of use; lower-priced models ($20–$50) require the user to inflate the cuff, while inflation is automatic on pricier models ($50–$125). Before purchasing a monitor, test it in the store to be sure it's easy to use.
Around-the-clock monitoring
Instead of asking you to invest in a home blood pressure monitoring unit, your doctor may send you home with a device that automatically takes your blood pressure every 15–30 minutes over the course of a 24-hour period and records the results. After reviewing the data, your doctor should have a better sense of your usual blood pressure.
This technology, called ambulatory blood pressure monitoring, isn't used often because it is cumbersome and many insurers haven't covered it in the past. But in 2001, a Medicare advisory committee recommended that Medicare pay for ambulatory blood pressure monitoring for people with suspected white-coat hypertension. So check with your health insurer about coverage.
Review Date: 2007-01-01
Harvard Medical School does not endorse products or services.
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