Secondary high blood pressure (secondary hypertension) is high blood pressure that's caused by another medical condition. It can be caused by conditions that affect the kidneys, arteries, heart or endocrine system. Secondary hypertension can also occur during pregnancy.

Secondary hypertension differs from the usual type of high blood pressure (primary hypertension or essential hypertension), which is often called simply high blood pressure.

Proper treatment of secondary hypertension can often control both the high blood pressure and the condition that causes it. Effective treatment reduces the risk of serious complications — including heart disease, kidney failure and stroke.

Like primary hypertension, secondary hypertension usually has no specific symptoms, even if blood pressure has reached dangerously high levels.

For people diagnosed with high blood pressure, having any of these signs may mean the condition is secondary hypertension:

• High blood pressure that doesn't respond to blood pressure medications (resistant hypertension)
• Very high blood pressure — systolic blood pressure over 180 millimeters of mercury (mm Hg) or diastolic blood pressure over 120 mm Hg
• High blood pressure that no longer responds to medication that previously controlled the blood pressure
• Sudden-onset high blood pressure before age 30 or after age 55
• No family history of high blood pressure
• No obesity

If you have a condition that can cause secondary hypertension, you may need your blood pressure checked more frequently. Ask your health care provider how often to have your blood pressure checked.

Many health conditions can cause secondary hypertension. Several kidney diseases may cause secondary hypertension, including:

• Diabetes complications (diabetic nephropathy). Diabetes can damage the kidneys' filtering system, which can lead to high blood pressure.
• Polycystic kidney disease. In this inherited condition, cysts in the kidneys interfere with kidney function and can raise blood pressure.
• Glomerular disease. Kidneys remove waste and sodium using tiny filters called glomeruli. In glomerular disease, these filters become swollen. This may raise blood pressure.

• Renovascular hypertension. This type of high blood pressure is caused by narrowing (stenosis) of one or both arteries leading to the kidneys.

  Renovascular hypertension is often caused by the same type of fatty plaques that can damage the coronary arteries (atherosclerosis) or a separate condition in which the muscle and fibrous tissues of the renal artery wall thicken and harden into rings (fibromuscular dysplasia).

Medical conditions affecting hormone levels also may cause secondary hypertension. These conditions include:

• Cushing syndrome. In this condition, corticosteroid medications may cause secondary hypertension, or hypertension may be caused by a pituitary tumor or other factors that cause the adrenal glands to produce too much of the hormone cortisol.
• Aldosteronism. The adrenal glands produce too much of the hormone aldosterone. This makes the kidneys retain salt and water and lose too much potassium, which raises blood pressure.
• Pheochromocytoma. This rare tumor, usually found in an adrenal gland, produces too much of the hormones adrenaline and noradrenaline. Having this tumor can lead to long-term high blood pressure or short-term spikes in blood pressure.
• Thyroid problems. When the thyroid gland doesn't produce enough thyroid hormone (hypothyroidism) or produces too much thyroid hormone (hyperthyroidism), high blood pressure can result.
• Hyperparathyroidism. The parathyroid glands control levels of calcium and phosphorus in the body. If the glands release too much parathyroid hormone, the amount of calcium in the blood rises — which triggers a rise in blood pressure.

Other possible causes of secondary hypertension include:

• Coarctation of the aorta. In this condition, present at birth, the body's main artery (aorta) is narrowed (coarctation). This forces the heart to pump harder to get blood through the aorta and to the rest of the body. As a result, blood pressure increases — particularly in the arms.

• Sleep apnea. In this condition, often marked by severe snoring, breathing repeatedly stops and starts during sleep, causing a lack of oxygen.

  Not getting enough oxygen may damage the lining of the blood vessel walls, which may make it harder for the blood vessels to control blood pressure. Also, sleep apnea causes part of the nervous system to be overactive and release certain chemicals that increase blood pressure.

• Obesity. As body weight increases, the amount of blood flowing through the body increases. This increase in blood flow puts added pressure on artery walls, increasing blood pressure.

  Being overweight also increases the heart rate and makes it harder for the blood vessels to move blood. In addition, fat deposits can release chemicals that raise blood pressure.

• Pregnancy. Pregnancy can make existing high blood pressure worse or cause high blood pressure to develop (pregnancy-induced hypertension or preeclampsia).

• Medications and supplements. Various prescription medications — such as pain relievers, birth control pills, antidepressants and drugs used after organ transplants — can cause or worsen high blood pressure in some people.

  Some decongestants and herbal supplements, including ginseng, licorice and ephedra (ma-huang), may have the same effect. Many illegal drugs, such as cocaine and methamphetamine, also increase blood pressure.

The greatest risk factor for developing secondary hypertension is having a medical condition that can cause high blood pressure, such as kidney, artery, heart or endocrine system problems.

Secondary hypertension can worsen the underlying medical condition that's causing the high blood pressure. Without treatment, secondary hypertension can lead to other health problems, such as:

• Damage to arteries. This can result in hardening and thickening of the arteries (atherosclerosis), which can lead to a heart attack, stroke or other complications.
• Aneurysm. Increased blood pressure can cause blood vessels to weaken and bulge, forming an aneurysm. If an aneurysm ruptures, it can be life-threatening.
• Heart failure. To pump blood against the higher pressure in the vessels, the heart muscle thickens. Eventually, the thickened muscle may have a harder time pumping enough blood to meet the body's needs, which can lead to heart failure.
• Weakened and narrowed blood vessels in the kidneys. This can prevent the kidneys from working properly.
• Thickened, narrowed or torn blood vessels in the eyes. This can result in vision loss.

• Metabolic syndrome. This syndrome is a cluster of disorders of the body's metabolism — including increased waist circumference, high triglycerides, low high-density lipoprotein (HDL) cholesterol (the "good" cholesterol), high blood pressure and high insulin levels.

  If you have high blood pressure, you're more likely to have other components of metabolic syndrome. The more components you have, the greater your risk of developing diabetes, heart disease or stroke.

• Trouble with memory or understanding. Uncontrolled high blood pressure also may affect the ability to think, remember and learn. Trouble with memory or understanding concepts is more common in people who have high blood pressure.

To diagnose secondary hypertension, a health care provider will take a blood pressure reading using an inflatable cuff.

A care provider might not diagnose secondary hypertension based on a single high blood pressure reading. It may take 3 to 6 high blood pressure measurements at separate appointments to diagnose secondary hypertension. Home blood pressure monitoring and ambulatory blood pressure monitoring might make up some of these readings. With ambulatory blood pressure monitoring, a device takes blood pressure measurements automatically at specific times throughout the day.

Other tests to help pinpoint the cause of the high blood pressure might include:

• Blood tests. Blood tests are often done to check levels of potassium, sodium, creatinine, blood glucose, and total cholesterol and triglycerides, among others.
• A urine test (urinalysis). A urine sample can contain markers that could point to medical conditions that cause high blood pressure.
• Ultrasound of the kidneys. Many kidney conditions are linked to secondary hypertension. In this noninvasive test, a technician moves a small, hand-held device called a transducer over the area to be tested. The transducer sends sound waves into the body, collects the ones that bounce back and sends them to a computer. The computer then creates images of the kidneys.

• Electrocardiogram (ECG or EKG). This painless noninvasive test records the electrical signals in the heart. This test can help determine whether a heart problem might be causing secondary hypertension.

  In this test, sensors (electrodes) are attached to the chest and sometimes to the limbs. The sensors connect to a computer that records the heart's electrical signal information and displays it as waves on a monitor or on paper. This test shows how the heart is beating.

Treatment for secondary hypertension involves treating the medical condition that's causing it with medications or surgery. Once the condition is treated, blood pressure might decrease or return to normal.

Treatment might require continuing to take blood pressure medication, as well. The underlying medical condition might affect this choice of medication.

Possible drug choices include:

• Thiazide diuretics. Diuretics, sometimes called water pills, are medications that help kidneys eliminate sodium and water. Thiazide diuretics are often the first — but not the only — choice in high blood pressure medications.

  Diuretics are often generic and tend to be less expensive than other high blood pressure medications. If you're not taking a diuretic and your blood pressure remains high, talk to your provider about adding one or replacing a drug you take with a diuretic. Possible side effects of diuretics include weakness, leg cramps and a higher risk of having sexual issues.

• Beta blockers. These medications reduce the workload on the heart and open the blood vessels. This causes the heart to beat slower and with less force. When prescribed alone, beta blockers don't work as well in Black people — but they're effective when combined with a thiazide diuretic.

  Possible side effects include fatigue, sleep problems, a slowed heart rate, and cold hands and feet. Beta blockers generally aren't used for people with asthma, as they can increase muscle spasms in the lungs.

• Angiotensin-converting enzyme (ACE) inhibitors. These medications help relax blood vessels by blocking the formation of a natural chemical that narrows blood vessels. ACE inhibitors may be especially important in treating high blood pressure in people with coronary artery disease, heart failure or kidney failure.

  Like beta blockers, ACE inhibitors don't work as well in Black people when prescribed alone, but they're effective when combined with a thiazide diuretic. Possible side effects include dizziness and coughing. ACE inhibitors should not be taken during pregnancy.

• Angiotensin II receptor blockers. These medications help relax blood vessels by blocking the action of a natural chemical that narrows blood vessels. Like ACE inhibitors, angiotensin II receptor blockers often are useful for people with coronary artery disease, heart failure or kidney failure.

  These medications have fewer potential side effects than do ACE inhibitors. Angiotensin II receptor blockers should not be used during pregnancy.

• Calcium channel blockers. These medications help relax the muscles of the blood vessels or slow the heart rate. Calcium channel blockers may work better for some people than ACE inhibitors or beta blockers alone. Possible side effects include water retention, dizziness and constipation.

  Grapefruit juice interacts with some calcium channel blockers, increasing levels of the medication in the blood and increasing the risk of side effects. Ask your health care provider or pharmacist if grapefruit juice affects your medication.

• Direct renin inhibitors. These medications relax and widen the arteries by preventing the action of a protein (enzyme) called renin. An example of a direct renin inhibitor is as aliskiren (Tekturna).

  Common side effects of aliskiren include dizziness and diarrhea. People with diabetes or moderate to severe kidney problems shouldn't use aliskiren in combination with ACE inhibitors or angiotensin II receptor blockers.

Treatment for secondary hypertension can sometimes be complicated. It might take more than one medication combined with lifestyle changes to control high blood pressure. Your health care provider will want to see you more often — possibly as often as once a month — until your blood pressure is controlled. Your provider may also recommend that you keep track of your blood pressure at home.

Healthy lifestyle changes are recommended to keep the heart healthy and blood pressure low. These include:

• Eating healthy foods. Try the Dietary Approaches to Stop Hypertension (DASH) diet, which emphasizes fruits, vegetables, whole grains and low-fat dairy foods. Get plenty of potassium, which is found in fruits and vegetables such as potatoes, spinach, bananas and apricots, to help prevent and control high blood pressure. Eat less saturated fat and total fat.

• Decreasing salt in the diet. A lower sodium intake — 1,500 milligrams (mg) a day — is appropriate for people 51 years of age and older and for people of any age who are Black or who have hypertension, diabetes or chronic kidney disease. Otherwise healthy people can aim for 2,300 mg a day or less.

  Reducing salt requires putting down the saltshaker and paying attention to the amount of salt in processed foods, such as canned soups or frozen dinners.

• Maintaining a healthy weight. If you're overweight, losing even 10 pounds (4.5 kilograms) can lower your blood pressure.
• Increasing physical activity. Regular physical activity can help lower blood pressure and keep weight under control. Strive for at least 30 minutes of physical activity a day.
• Limiting alcohol. Even if you're healthy, alcohol can raise your blood pressure. If you choose to drink alcohol, do so in moderation. For healthy adults, that means up to one drink a day for women and two drinks a day for men.
• Not smoking. Tobacco injures blood vessel walls and speeds up the process of hardening of the arteries. If you smoke, ask your health care provider to help you quit.
• Managing stress. Reduce stress as much as possible. Practice healthy coping techniques, such as muscle relaxation and deep breathing. Getting plenty of sleep can help, too.

High blood pressure may be discovered during a routine physical. At that point, your primary care provider may order more tests or refer you to a provider who specializes in treating the suspected cause of your high blood pressure. For example, if your provider believes that a kidney problem is causing your high blood pressure, you'll likely be referred to a doctor who specializes in treating kidney disorders (nephrologist).

Here's some information to help you get ready for your appointment.

What you can do

• Be aware of any pre-appointment restrictions. When you make the appointment, ask if there's anything you need to do in advance, such as restrict your diet for a certain number of hours before your appointment.
• Write down your symptoms, including any that may seem unrelated to the reason for which you scheduled the appointment, and when they began.
• Write down key personal information, including major stresses or recent life changes.
• Make a list of all medications, vitamins or supplements you take, including doses.
• Write down questions to ask your provider.

For secondary hypertension, some basic questions to ask include:

• What do you think is causing my high blood pressure?
• What tests do I need? Do these tests require any special preparation?
• Is my high blood pressure temporary or long lasting?
• I have other health conditions. How can I best manage these conditions together?
• Are there dietary or activity restrictions that I need to follow?
• How often do I need to come back to have my blood pressure checked?
• Do I need to check my blood pressure at home? If so, how often?
• Which type of blood pressure machine is best? Can you help me learn how to use it correctly?
• Are there brochures or other printed material that I can have? What websites do you recommend?

Don't hesitate to ask other questions.

What to expect from your doctor

Your provider is likely to ask you questions, including:

• Has anyone in your family ever been diagnosed with high blood pressure?
• If yes, do you know the reason for the high blood pressure? For example, does your relative have diabetes or kidney problems?
• Have you had unusual symptoms?
• How much salt is in your diet?
• Has your body weight changed recently?
• If you were ever pregnant, was your blood pressure higher during pregnancy?