Sometimes, the simplest tools in medicine are the ones that give us the most useful information.

Take the humble blood pressure machine, for example. It’s been around for years, and it’s cheap, compared with a lot of other medical devices. It’s simple to use, and it doesn’t require a medical or a nursing degree to operate. But the numbers it reports are valuable in helping predict a person’s risk of a host of medical problems, including heart failure, stroke and kidney failure, and can help doctors determine whether a person really needs to take medicine to control his or her high blood pressure.

In recent years, many physicians have concluded that just checking blood pressure in the doctor’s office or clinic isn’t sufficient. A “Call to Action” from the American Heart Association (AHA), the American Society of Hypertension (ASH), and the Preventive Cardiovascular Nurses Association (PCNA) recommends that most people who have been diagnosed with high blood pressure, as well as people whose blood pressure is slightly elevated but not yet in the “high blood pressure” range, get a monitor and check their blood pressure regularly at home.

Because they’re taken in a familiar environment, home blood pressure readings tend to be lower than the measurements taken in a doctor’s office or clinic, and better reflect a person’s true blood pressure. They give doctors and nurses a better sense of how well a person’s treatment is working, compared with sporadic readings taken in the office, and may enable some people to avoid medication entirely. In a few cases, they also help detect the opposite — blood pressure that’s in an abnormally high range at home, even though it seems normal during visits to the office. Home blood pressure monitoring can also help people save money and avoid missing work time, by reducing the number of visits they have to make to the doctor’s office or clinic.

“There’s emerging evidence that home blood pressure readings are good predictors of cardiovascular outcomes for most people,” said Dr. Mahboob Rahman, an associate professor and hypertension researcher at Case Western Reserve University and University Hospitals Case Medical Center in Cleveland. “Patients are probably further along (in the habit of checking home blood pressure) than physicians, but we need to provide them with guidance.”

Below are some suggestions from Dr. Rahman, as well as from the AHA/ASH/PCNA “Call to Action” statement, regarding the best way to check your blood pressure accurately:

1. Pick a blood pressure machine that gives automatic readings and that’s been “validated,” meaning it’s been tested for accuracy according to a widely accepted set of standards. Dr. Rahman recommends a nonprofit website, Dableducational.org, which lists monitors that have been tested according to the standards of the European Society of Hypertension. It’s also helpful to get a machine that will keep a log of your readings so that you’ll have something to show your doctor or nurse practitioner.

2. Arm monitors — meaning, machines with a “cuff,” or sleeve that fits on the upper arm — tend to be more accurate than wrist monitors, according to the “call to action” statement, and finger monitors should generally be avoided. Wrist monitor readings can change with the position of the wrist. The wrist needs to be held at the level of the heart to get the most accurate reading.

3. Make sure the cuff — the sleeve of the machine that fits around your arm — is the correct size for your arm. The inflatable part of the sleeve should fit around 80 percent of your upper arm. If your arms are large, you may need to buy a large cuff separately.

Before using the machine, bring it to your clinic or doctor’s office so that the staff can check its accuracy and make sure you know how to operate it correctly. The American Academy of Family Physicians and British Hypertension Society also post online instructions that can help orient you when you begin using your machine.

4. Basic rules for checking blood pressure (in the clinic as well as at home) include sitting in a chair that supports the back, with both feet in a comfortable position on the ground, for five minutes before taking the measurement. Smoking, exercising and drinking coffee should be avoided for half an hour prior to the reading, since these can make blood pressure levels rise transiently. If you need to use the toilet, do so before you check your blood pressure — don’t take a reading when your bladder is full. Try to relax.

5. Check your blood pressure two to three times a week, at times when you are relatively calm. The “call to action” statement recommends that doctors review at least 12 recordings prior to making any decisions about beginning, stopping, or adjusting medication. The statement also says that a home value of 135/85 or above is high, as opposed to the 140/90 level that’s usually considered elevated. For people with diabetes and other conditions that increase their risk of heart disease, the goal blood pressure is 130/80 or lower.

6. Remember, the goal of checking your blood pressure at home is to keep an overall record that will help your doctor or nurse decide on what treatment to recommend. Home monitoring is not meant to figure out why you might feel ill at any one particular moment. “Some people get in the habit of ‘I’m not feeling well, so I’ll check to see if my blood pressure is high or low,” Dr. Rahman said. “That’s not the best use of the blood pressure machine.” If you’re not feeling well, call your doctor or nurse so that they can diagnose the reason why.

7. Don’t panic if the levels fluctuate. In most people, blood pressure tends to be a bit higher in the morning and at work, and it’s normal for them to ebb and flow. “The variability of readings is high,” the joint statement explains. “Individual high or low readings have little, if any, significance.”

8. Bring your machine back to your doctor’s office every year, so that the staff can make sure it’s still working accurately.

9. Don’t rely on the free blood pressure monitors available at the grocery store or pharmacy, as they aren’t always accurate. If you can’t afford to buy your own machine, check with your local fire department to see if they offer “drop-in” times when you can get your blood pressure checked.

Don Wiggins, a 60 year old radio host and sales manager, uses a $50, battery-powered machine to check his blood pressure, and says it’s an important part of his daily routine. He began recording his blood pressure 3 years ago, after he underwent emergency heart bypass surgery. A home nurse showed him how to use his blood pressure monitor. “At that point, I was ready to listen to anybody,” he recalled recently. “But the machines are so easy. There’s really no excuse for anyone not to check his or her blood pressure.”

“High blood pressure is very prevalent, especially among African-American men,” he added. “It’s a silent killer, and it’s important to keep it under check.”

Erin Marcus is an internal medicine physician and writes at New America Media.  This article originally appeared in The Huffington Post and New America Media.

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