Secondary hypertension (secondary high blood pressure) is high blood pressure that is caused by another medical condition. Secondary hypertension differs from the usual type of high blood pressure (essential hypertension), which is often referred to simply as high blood pressure. Essential hypertension, also known as primary hypertension, has no clear cause and is thought to be linked to genetics, poor diet, lack of exercise and obesity.

Secondary hypertension can be caused by conditions that affect your kidneys, arteries, heart or endocrine system. Secondary hypertension can also occur during pregnancy.

Secondary hypertension tends to appear suddenly. But there's good news. Proper treatment can often control both the underlying condition and the high blood pressure, which reduces the risk of serious complications — including heart disease, kidney failure and stroke.

Like primary high blood pressure (hypertension), secondary hypertension usually has no specific signs or symptoms, even if your blood pressure has reached dangerously high levels.

Although a few people with early-stage high blood pressure may have dull headaches, dizzy spells or a few more nosebleeds than normal, these signs and symptoms typically don't occur until high blood pressure has reached an advanced — even life-threatening — stage.

If you're diagnosed with high blood pressure, having any of these signs may mean your 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 a diastolic blood pressure over 110 mm Hg
• A blood pressure medication that previously controlled your blood pressure no longer works
• Sudden-onset high blood pressure before age 20 or after age 50
• No family history of high blood pressure

When to see a doctor
If you have a condition that can cause secondary hypertension, you may need your blood pressure checked more frequently. Ask your doctor how often you should have your blood pressure checked.

Unless you have symptoms of extremely high blood pressure, there's probably no need to make a special trip to the doctor to have your blood pressure checked.

A number of medical conditions can cause secondary hypertension. These include:

• Diabetes complications (diabetic nephropathy). Your kidneys contain millions of tiny blood vessels that filter waste from your blood and get rid of it through your urine. But diabetes can damage this filtering system. In fact, diabetic nephropathy is the most common type of kidney failure — which is nearly always associated with high blood pressure. The high blood pressure can be treated with diet, exercise and medication.
• Polycystic kidney disease. In this inherited condition, cysts in your kidneys prevent them from working normally, and can raise blood pressure. The high blood pressure can be treated with diet, exercise and medication.
• Glomerular disease. Your kidneys filter waste and sodium using microscopic filters called glomeruli. Swelling of these filters is called glomerulonephritis. If the swollen glomeruli can't work normally, you may develop high blood pressure. The high blood pressure can be treated with diet, exercise and medication. Glomerulonephritis may be treated with medication, and if needed, with dialysis or a kidney transplant.
• Hydronephrosis. In this condition, certain parts of one or both kidneys become plugged due to kidney stones, a tumor or other reasons. This blocks urine flow and raises blood pressure. Some blockages resolve without treatment, but others require drainage or surgery. Once the blockage is removed, blood pressure often returns to normal.

• Renovascular hypertension. This is a type of secondary hypertension caused by narrowing (stenosis) of one or both arteries leading to your kidneys. Renovascular hypertension can cause severe hypertension and irreversible kidney damage. It's often caused by the same type of fatty plaques that can damage your coronary arteries (atherosclerosis) or a condition in which the muscle and fibrous tissues of the renal artery wall thicken and harden into rings (fibromuscular dysplasia).

  In mild cases, the high blood pressure may be treated with diet, exercise and medication while kidney function is simply monitored. In more severe cases, the doctor may open clogged arteries with a procedure known as angioplasty. Wire mesh tubes (stents) may be used to hold the arteries open. Another option is to surgically bypass blood flow around the affected arteries. Once blood flow to the kidneys improves, blood pressure usually returns to normal.

• Cushing's syndrome. In this condition, corticosteroid medications, a pituitary tumor or other factors cause the adrenal glands to produce too much of the hormone cortisol. This raises blood pressure. Treatment may include surgery, radiation therapy or medication to return both cortisol and blood pressure to normal.
• Aldosteronism. In this condition, a tumor in the adrenal gland, increased growth of normal cells in the adrenal gland or other factors cause the adrenal glands to release an excessive amount of the hormone aldosterone. This makes your kidneys retain salt and water and lose too much potassium, which raises blood pressure. Treatment may include medication to block the action of aldosterone, surgery to remove a tumor in the adrenal gland, and diet, exercise and medication to treat the high blood pressure.
• Pheochromocytoma. This rare tumor in the adrenal gland increases production of the hormones adrenaline and noradrenaline, which can lead to long-term high blood pressure or short-term spikes in blood pressure. Surgery to remove the tumor usually returns your blood pressure to normal.
• Hypothyroidism. This condition occurs when the thyroid gland doesn't produce enough thyroid hormone, which can cause high blood pressure. Hypothyroidism may have various causes, including inflammation, surgery, radiation treatment, certain medications or pituitary problems. Treatment with synthetic thyroid hormones usually returns blood pressure to normal.
• Hyperthyroidism. This condition occurs when the thyroid gland produces too much thyroid hormone. This can increase the activity of epinephrine and norepinephrine, which can increase blood pressure. Treatment may include medication, radioactive iodine therapy or surgery, all of which can restore normal blood pressure.
• Hyperparathyroidism. The parathyroid glands regulate levels of calcium and phosphorus in your body. If the glands secrete too much parathyroid hormone, the amount of calcium in your blood rises — which triggers a rise in blood pressure. Treatment is typically removal of the parathyroid glands, which returns blood pressure to normal.
• Coarctation of the aorta. With this defect you're born with, 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 your body. This, in turn, raises blood pressure — particularly in your arms. Surgery to repair the aorta can restore normal blood pressure.
• Sleep apnea. In this condition, often marked by severe snoring, breathing repeatedly stops and starts during sleep, meaning you don't get enough oxygen. Not getting enough oxygen may damage the lining of the blood vessel walls, which may make your blood vessels less effective in regulating your blood pressure. Treating sleep apnea with a pressure mask, devices you wear on your nose, surgery, weight loss or other steps can help control the high blood pressure.
• Obesity. As you gain weight, the amount of blood circulating through your body increases. This puts added pressure on your artery walls, increasing your blood pressure. In addition, excess weight often is associated with an increase in heart rate and a reduction in the capacity of your blood vessels to transport blood. All of these factors can increase blood pressure.
• Preeclampsia. This pregnancy complication, characterized by protein in the urine and elevated blood pressure, can develop after the 20th week of pregnancy. Left untreated, preeclampsia can lead to life-threatening complications for both mother and baby. The only cure for preeclampsia is delivery of the baby, which restores normal blood pressure.
• Medications and supplements. Various prescription medications — from pain relievers to antidepressants and drugs used after organ transplants — can cause or aggravate high blood pressure in some people. Birth control pills, decongestants and certain herbal supplements, including ginseng and St. John's wort, may have the same effect. Many illicit drugs, such as cocaine and methamphetamine, also increase blood pressure.

The greatest risk factor for having 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 you have that's causing your high blood pressure. If you don't receive treatment, secondary hypertension can also cause other medical conditions, such as:

• Damage to your 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 your 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 your vessels, your heart muscle thickens. Eventually, the thickened muscle may have a hard time pumping enough blood to meet your body's needs, which can lead to heart failure.
• Weakened and narrowed blood vessels in your kidneys. This can prevent these organs from functioning normally.
• 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 your body's metabolism — including increased waist circumference, high triglycerides, low high-density lipoprotein (HDL), or "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 your ability to think, remember and learn. Trouble with memory or understanding concepts is more common in people who have high blood pressure.

If your doctor thinks you have secondary hypertension, you'll likely need an appointment to confirm that you have the condition. Your doctor may order blood tests, urinalysis, an ultrasound or an electrocardiogram as part of your appointment.

Your doctor should tell you if there are any special instructions to follow before your tests. You may have to fast for nine to 12 hours if you're having a blood test so that your doctor gets the most accurate results.

Your doctor may also ask about your family history of high blood pressure. If you don't have a family history of high blood pressure, it's possible your blood pressure could be caused by another medical condition.

To diagnose secondary hypertension, your doctor will first take a blood pressure reading using an inflatable cuff, just as your blood pressure is measured during a typical doctor's appointment. Your doctor may not diagnose you with secondary hypertension based on one higher than normal blood pressure reading — it often takes at least three consecutive high blood pressure measurements at separate appointments to diagnose secondary hypertension.

Your doctor will also want to check other markers to pinpoint the cause of your high blood pressure. These could include:

• A blood test. Your doctor may want to check your potassium, sodium, total cholesterol and triglycerides, and other chemicals in your blood to help make a diagnosis.
• Urinalysis. Your doctor may want to check your urine for markers that could show your high blood pressure is caused by another medical condition.
• Ultrasound of your kidneys. Since many kidney conditions are linked to secondary hypertension, your doctor may order an ultrasound of your kidneys. In this noninvasive test, a technician will run an instrument called a transducer over your skin. The transducer, which produces sound waves, measures how the sound waves bounce off your kidneys and sends images created by the sound waves to a computer monitor.
• Electrocardiogram (ECG). If your doctor thinks your secondary hypertension may be caused by a heart problem, he or she may order an electrocardiogram. In this noninvasive test, sensors (electrodes) that can detect the electrical activity of your heart are attached to your chest and sometimes to your limbs. An ECG measures the timing and duration of each electrical phase in your heartbeat.

Once an underlying condition is effectively treated, secondary hypertension may decrease or even return to normal. Often, however, lifestyle changes — such as eating healthy foods, increasing physical activity and maintaining a healthy weight — can help keep your blood pressure low.

You may need to continue to take blood pressure medication as well, such as:

• Thiazide diuretics. Diuretics, sometimes called water pills, are medications that act on your kidneys to help your body eliminate sodium and water, reducing blood volume. Thiazide diuretics are often the first — but not the only — choice in high blood pressure medications. If you're not taking a diuretic and your blood pressure remains high, talk to your doctor about adding one or replacing a drug you currently take with a diuretic.
• Beta blockers. These medications reduce the workload on your heart and open your blood vessels, causing your heart to beat slower and with less force. When prescribed alone, beta blockers don't work as well in blacks — but they're effective when combined with a thiazide diuretic.
• 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 blacks when prescribed alone, but they're effective when combined with a thiazide diuretic.
• Angiotensin II receptor blockers. These medications help relax blood vessels by blocking the action — not the formation — 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 and kidney failure.
• Calcium channel blockers. These medications help relax the muscles of your blood vessels. Some slow your heart rate. Calcium channel blockers may work better for blacks than do ACE inhibitors or beta blockers alone. A word of caution for grapefruit lovers, though. Grapefruit juice interacts with some calcium channel blockers, increasing blood levels of the medication and putting you at higher risk of side effects. Talk to your doctor or pharmacist if you're concerned about interactions.

Treatment can sometimes be complicated. But once you know you have high blood pressure, you can work with your doctor to control it.

Although lowering secondary hypertension can be difficult, making the same lifestyle changes you would make if you had primary high blood pressure can help. These include:

• Eat 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 can help prevent and control high blood pressure. Eat less saturated fat and total fat.
• Decrease the salt in your diet. Although 2,400 milligrams (mg) of sodium a day is the current limit for otherwise healthy adults, limiting sodium intake to 1,500 mg a day will have a more dramatic effect on your blood pressure. While you can reduce the amount of salt you eat by putting down the saltshaker, you should also pay attention to the amount of salt that's in the processed foods you eat, such as canned soups or frozen dinners.
• Maintain a healthy weight. If you're overweight, losing even 5 pounds (2.3 kilograms) can lower your blood pressure.
• Increase physical activity. Regular physical activity can help lower your blood pressure and keep your weight under control. Strive for at least 30 minutes of physical activity a day.
• Limit alcohol. Even if you're healthy, alcohol can raise your blood pressure. If you choose to drink alcohol, do so in moderation — up to one drink a day for women and everyone over age 65, and two drinks a day for men.
• Don't smoke. Tobacco injures blood vessel walls and speeds up the process of hardening of the arteries. If you smoke, ask your doctor to help you quit.
• Manage 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.