Hypertension is diagnosed when blood pressure consistently measures >130 mmHg systolic and >80 mmHg diastolic. Blood pressure is measured using a blood pressure cuff, which is a non-invasive device that can detect the pressure inside your arteries, conveying numerical values using a sphygmomanometer or an electronic device. Your doctor may also use lab tests or imaging tests to diagnose some of the causes or complications of hypertension.
Labs and Tests
Your blood pressure fluctuates from minute to minute during the course of the day in response to your activity level, fluid status, anxiety level, and many other factors. This means that one reading at your doctor’s office is just that—a moment in time. An average of readings typically provides a more accurate picture of your blood pressure status. Your doctor may also order blood or urine tests if secondary hypertension is suspected.
Blood Pressure Tests
Traditionally, blood pressure is measured at the doctor’s office using a blood pressure cuff, which can be attached to a sphygmomanometer that uses mercury for measuring blood pressure, or to an electronic reading device. The blood pressure cuff is compressed to squeeze and then release external pressure on an artery in your arm, measuring your maximal pressure right when your heart beats (systolic pressure) and your lowest pressure, which occurs when your heart relaxes (diastolic pressure).
A diagnosis of hypertension usually requires at least three elevated blood pressure readings taken at least one week apart.
Going back for repeat testing, however, can be a burden, and your health insurance may not approve these repeat visits. Because of this, some doctors may rely on in-office readings as well as at-home test results (see below) to help determine whether or not you have hypertension, particularly when the diagnosis is not completely clear.
Resting blood pressure is considered the most accurate reading. To get this measurement:
- Your blood pressure should be recorded in a quiet, warm environment after you have been sitting quietly for at least five minutes with your feet supported.
- You should not have used caffeine or tobacco products for at least 30 minutes prior to the test.
- Your doctor may take at least two blood pressure readings, preferably at least five minutes apart. If the readings vary by more than 5 mmHg, further readings may be done until closer readings are obtained. The purpose is to get a consistent reading, not to average widely ranging measures.
Some people have elevated resting blood pressures in the doctor’s office, but have normal resting blood pressures at other times. This pattern has been called white coat hypertension, and it usually occurs due to anxiety. Repeat checks may be necessary if this occurs.
Once your blood pressure is measured accurately, your doctor will classify the results, depending on your systolic and diastolic blood pressure values, as follows:
- Normal blood pressure: systolic pressure <120 mmHg and diastolic pressure <80 mmHg
- Hypertension: systolic pressure >129 or diastolic pressure >79 mmHg
The category of hypertension is further divided into two stages:
- Stage 1 hypertension: systolic pressure of 130 mmHg to 139 mmHg or diastolic pressure of 80 mmHg to 89 mmHg
- Stage 2 hypertension: systolic pressure >139 mmHg or diastolic pressure >89 mmHg
Readings great than this indicate serious concerns:
- Hypertensive urgency: systolic blood pressure of >220 mm Hg and a diastolic blood pressure of >120 mmHg without major symptoms
- Hypertensive emergency: systolic blood pressure of >180 mmHg or a diastolic pressure of >120 mmHg with signs of organ failure, such as dizziness, confusion, and shortness of breath (This can occur suddenly at any time, and would not necessarily be diagnosed at a scheduled doctor’s visit.)
Blood tests may be needed to determine if you have secondary hypertension due to a serious or treatable health condition. Blood tests that may be ordered to assist in the diagnosis of hypertension include:
- Electrolyte levels
- Blood glucose
- Thyroid function tests
- Kidney function tests: blood urea nitrogen (BUN) and creatinine levels
Urine tests can help determine if diabetes, kidney failure, or illegal drugs are causing or contributing to high blood pressure.
Hypertension Doctor Discussion Guide
Get our printable guide for your next doctor’s appointment to help you ask the right questions.
Devices that measure blood pressure using a traditional blood pressure cuff are becoming more accessible and easy to use. Many can record and keep track of your blood pressure readings—helpful to you as you monitor hypertension, but also potentially useful to your doctor as he works to diagnose it from the outset.
Home Blood Pressure Monitoring (HBPM)
You can measure your own blood pressure at home, a process referred to as home blood pressure monitoring (HBPM). HBPM has become much easier and more accurate in recent years, and it is now a viable option for diagnosing hypertension and helping manage it once identified.
This is particularly helpful for those who experience white coat hypertension, as your blood pressure should be normal at home and readings taken in that setting can make it clear that in-office results are moot, rendering treatment unnecessary. Furthermore, if you have fluctuating hypertension that requires treatment, home monitoring can pick that up even if your in-office blood pressure checks do not.
HBPM uses easy-to-use, electronic blood pressure devices that are readily available and cost $40 to $50, though prices vary.
Ambulatory Blood Pressure Monitoring (APBM)
An ABPM device consists of a blood pressure cuff that is worn on the arm and attached to a recording device, which can be worn on a belt.
Remember, hypertension is most accurately determined by average blood pressure during an entire day. ABPM takes and logs blood pressure at 15-minute or 30-minute intervals over a 24- or 48-hour period. This means that the blood pressure fluctuations that normally occur in a day can be accounted for as your doctor assesses your recorded average.
At the same time, if you have fluctuating hypertension, your doctor would be able to pick that up using APBM because the measures span a longer time period than measures in the office. The diagnosis of hypertension with ABPM has been well-validated and is more accurate for diagnosing stage 1 hypertension than a single visit to the doctor’s office.
Imaging and Other Tests
Blood pressure is very closely tied to heart and kidney function, and imaging tests can assist in the diagnosis of hypertension and its associated causes and complications.
An EKG is a fairly simple and rapid test that assesses your heart rhythm. Heart rhythm abnormalities can cause high blood pressure. Likewise, hypertension can produce long-term changes that result in heart rhythm abnormalities.
Your heart function can be examined using an imaging test that visualizes your heart as it moves. Excessively high blood pressure may produce changes that can be identified using echocardiography, and some heart function abnormalities can produce high blood pressure.
A test that is useful for evaluating the kidneys and the blood vessels, an ultrasound may be needed if your doctor is concerned about certain aspects of your blood flow. For example, if your doctor believes that you may have excessive narrowing in one or more of your blood vessels, this can be evaluated using an ultrasound.
CAT Scan or MRI
If your doctor suspects a tumor as the cause of your high blood pressure, you may need to have an imaging test, such as CAT scan or MRI, usually to evaluate the kidneys or adrenal glands.
Hypertension is diagnosed when blood pressure is consistently elevated, and hypertensive emergency can be diagnosed based on very high blood pressure, even if it is not recurrent. There are some conditions that can produce consistently high blood pressure or severe high blood pressure, even if hypertension itself is not present, which your doctor will need to consider:
- Medication or drug side effect: Medications and drugs can produce hypertension, and the blood pressure may return to normal once one is discontinued. It can be difficult to know if medication is the cause of your high blood pressure. Be sure to tell your doctor about all medications and recreational drugs that you use, as even some herbal remedies are associated with hypertension.
- Kidney failure: Acute or chronic kidney failure can raise blood pressure. If kidney failure is the only cause of hypertension, blood pressure can return to normal when fluid and electrolyte levels are restored to normal. Kidney failure is treated with medication, dialysis, or a transplant.
- Hyperthyroidism: High thyroid levels can cause high blood pressure, as well as weight loss, increased appetite, sweats, and jitteriness. Thyroid abnormalities are normally diagnosed using blood tests to assess thyroid hormone levels.
- Pheochromocytoma: A tumor of the adrenal gland, a pheochromocytoma causes excessive production of epinephrine and norepinephrine, resulting in a sense of anxiety, sweating, racing heart, and high blood pressure. Diagnosis is usually made through clinical observation of signs and symptoms, blood tests that measure hormones, and an imaging test of the adrenal glands, which are small organs located above the kidneys.