Definition

Secondary hypertension is defined as hypertension (high blood pressure) caused by another known disease or condition. Secondary hypertension can be caused by issues with the kidneys, blood vessels, heart, or endocrine (hormone) system. Secondary hypertension can also occur during pregnancy. On the other hand, if high blood pressure has no known cause, it is referred to as essential or primary hypertension.

Secondary hypertension is quite rare, accounting for only 5 to 10% of the total population, so it can be difficult to detect.  Proper treatment will often control the underlying condition and lower high blood pressure, thereby reducing the risk of serious complications (including heart disease, kidney failure, and stroke).

Hypertension itself is a common condition characterized by a higher amount of pressure than normal. Blood pressure is usually measured with a sphygmomanometer placed around your arm. In a blood pressure check, two measurements will be sought, namely:

• Systolic blood pressure is the pressure of the blood vessels during the heartbeat
• Diastolic blood pressure is the pressure of the blood vessels between heartbeats

Systolic and diastolic values are recorded simultaneously, with the systolic blood pressure being recorded first and the diastolic blood pressure second. A normal blood pressure measurement is 120/80 mmHg (systolic/diastolic) or less.

Causes

Secondary hypertension is caused by the presence of another underlying condition or disease. There are many different conditions or diseases that can cause secondary hypertension, including:

• Kidney disease: Injury to the kidneys or blood vessels that are too narrow can lead to poor blood supply to the organ. This can trigger higher production of a hormone called Renin. Renin causes the production of substances in the body (such as the protein molecule angiotensin II) that can increase blood pressure
• Adrenal gland disease: The adrenal glands are glands located above the kidneys that produce and regulate hormones in the body. When there is a problem with these glands, the hormones in the body can become unbalanced and cause several conditions, which include:
• Pheochromocytoma: a tumor of the adrenal gland that overproduces the hormones Epinephrine and Norepinephrine
• Conn's syndrome or primary aldosteronism: a condition where the body makes too much of the hormone Aldosterone (a hormone that regulates salt and fluid balance in the body)
• Cushing's syndrome: a condition where there is too much Cortisol (a hormone that regulates carbohydrate metabolism and blood pressure)
• Hyperparathyroidism: In this condition, the parathyroid glands (located in the neck) overproduce hormones that regulate calcium levels in the blood, and this condition can lead to high blood pressure
• Disorders of the thyroid gland: Abnormal functioning of the thyroid gland can also lead to high blood pressure
• Coarctation of the aorta: A narrowing or tightening of the aortic blood vessel, which is the largest blood vessel on the left side of the heart and carries blood throughout the body. Coarctation can restrict normal blood flow
• Obstructive sleep apnea: In this condition, a person often wakes up from sleep and stops breathing during sleep due to a blockage in the upper airway
• Side effects of certain medications can also lead to secondary hypertension. Such medications include:
• Hormonal contraceptives (birth control pills)
• Non-steroidal anti-inflammatory drugs (NSAIDs)
• Slimming medicines
• Stimulant drugs
• Antidepressant drugs
• Immune system suppressant drugs
• Decongestants (medicine to relieve nasal congestion)

Risk Factor

The most significant risk factor for secondary hypertension is having underlying medical conditions that cause blood pressure to rise. Secondary hypertension is relatively rare, and screening for the cause can be costly and time-consuming, so not every patient with high blood pressure will be tested for the condition.

Several factors can help determine whether you should be screened for secondary hypertension, including:

• Age, particularly in patients who are under 30 years old and have high blood pressure without a family history or other risk factors for high blood pressure
• Resistant hypertension, particularly in patients with high blood pressure that does not improve despite optimal treatment with at least three antihypertensive drugs
• Obesity, particularly in overweight patients with high blood pressure that does not respond to treatment over time
• Signs or symptoms suggestive of an underlying medical condition or disease
• Have abnormal laboratory results such as low potassium or high calcium levels

Symptoms

Secondary hypertension usually does not show any specific signs or symptoms, even if your blood pressure has reached very high levels. Hypertension can usually be identified by performing a blood pressure check. The American Heart Association defines hypertension as a blood pressure of 130/80 mmHg or higher. If you have been diagnosed with high blood pressure, any of the following signs may indicate that your hypertension is secondary:

• High blood pressure that does not respond to antihypertensive drugs (resistant hypertension)
• Having very high blood pressure, where the systolic blood pressure is more than 180 mmHg or the diastolic blood pressure is more than 120 mmHg
• High blood pressure that no longer responds to medications that previously controlled your blood pressure
• Sudden onset of high blood pressure before age 30 or after age 55
• No family history of high blood pressure
• No obesity

Diagnosis

When diagnosing secondary hypertension, the doctor will first conduct an interview to ask about your symptoms and look for risk factors and causes that may contribute to the onset of secondary hypertension. The doctor will then perform a physical examination, including measuring your blood pressure. The doctor may also look for physical signs such as weight changes, fluid buildup (swelling), abnormal hair growth, stretch marks on the abdominal skin, and abnormal blood flow to the kidneys.

Hypertension cannot be diagnosed immediately based on a single elevated blood pressure reading. It may take three to six high blood pressure measurements taken at separate appointments to diagnose secondary hypertension. These measurements may come from home blood pressure monitoring or hospital outpatient blood pressure monitoring.

The doctor may also suggest some additional tests to determine the cause of your high blood pressure. These tests may include:

• Blood tests. These are often done to check the levels of potassium, sodium, creatinine, blood glucose, total cholesterol, and triglycerides
• Urine test (urinalysis). To look for certain markers that the high blood pressure is caused by another medical condition
• Ultrasound of the kidneys. There are many kidney disorders associated with secondary hypertension. This examination uses a device that utilizes sound waves to view images of the kidney structure
• Electrocardiogram (ECG). This can monitor electrical signals in the heart to determine whether any heart problems are causing secondary hypertension

Management

Management of secondary hypertension will depend on the underlying conditions that cause it. Secondary hypertension will persist as long as you have the underlying secondary conditions. Some of the measures you can take to control high blood pressure while undergoing treatment for the underlying condition include:

• Eating a healthy diet that is low in salt
• Exercising regularly
• Stop smoking
• Maintaining an ideal body weight
• Limiting alcohol consumption

When secondary hypertension is caused by the presence of a tumor, surgical intervention may be necessary to treat the condition. In cases of hormonal imbalance and other conditions, medications may be used to treat secondary hypertension. Furthermore, you may need to continue taking antihypertensive medications, and the underlying medical condition of secondary hypertension will influence your drug selection. Your doctor may choose from the following classes of antihypertensives:

• Thiazide diuretics
• Beta Blockers
• Angiotensin-converting enzyme (ACE) inhibitors
• Angiotensin II Receptor Blockers
• Calcium Channel Blockers
• Direct Renin Inhibitors

Complications

Secondary hypertension can worsen the underlying medical condition that causes blood pressure to be high. If left untreated, secondary hypertension can lead to other health problems, such as:

• Damage to blood vessels which leads to heart attack, stroke, or other complications
• Aneurysms (weakened and bulging blood vessels)
• Heart failure
• Weakened and narrowed blood vessels in the kidneys
• Thickened, narrowed, or torn blood vessels in the eyes
• Metabolic syndrome is a group of metabolic disorders, including increased waist circumference, high triglyceride levels, low levels of good fats (HDL), high blood pressure, and high insulin levels
• Impaired memory or comprehension

Prevention

Several causes of secondary hypertension, such as tumors or abnormal blood vessel structure, cannot be prevented. Other causes of this condition, such as medication use or excess body weight, can be prevented by adopting a healthier lifestyle and being aware of potential medication side effects.

When to See a Doctor?

If you have a condition that can lead to secondary hypertension, you should get your blood pressure checked on a regular basis. Consult with a doctor to get the right treatment.