Tests
The goals with testing are to detect high blood pressure, confirm that it is persistent over time, determine whether it is being caused by an underlying medical condition that may be able to be resolved or controlled, evaluate the status of body organs, get a baseline of organ health prior to the start of drug therapies, and to monitor hypertension control and organ status over time.
Laboratory Tests
Laboratory testing is not diagnostic for hypertension, but general tests are frequently ordered to help evaluate and monitor organ function and specific tests are ordered, as indicated, to detect conditions that may be causing and/or exacerbating high blood pressure.
General tests that may be ordered include:
Urinalysis - ordered to help assess kidney function
Hematocrit – may be ordered as part of the Complete Blood Count (CBC) to evaluate the ratio of fluid to solids in the blood
BUN (Blood Urea Nitrogen) and/or Creatinine – to detect and monitor kidney dysfunction or to monitor the effect of medications on the kidneys
Potassium – may be ordered as part of the Electrolyte panel, which also includes sodium, chloride, and carbon dioxide (CO2); used to evaluate and monitor the balance of the body’s electrolytes; some high blood pressure medications can upset the balance by causing excessive sodium and potassium loss
Fasting Glucose – ordered to determine if blood glucose levels are within healthy ranges
Calcium – may be ordered to determine how much total calcium or ionized calcium is circulating in the blood; increased activity of the parathyroid glands, which produces an increase in serum calcium, is associated with hypertension
TSH (Thyroid Stimulating Hormone) and T4 – may be ordered to detect and monitor thyroid dysfunction
Lipid Profile – may be ordered to evaluate levels of total cholesterol, HDL cholesterol, LDL cholesterol and triglycerides
The Basic Metabolic Panel (BMP) includes several of these tests as well, so it may be ordered instead of the individual tests.
Specific tests that may be ordered (based on the patient’s medical history, physical findings, and routine laboratory test results) to help detect, diagnose, and monitor conditions causing secondary hypertension include:
Aldosterone and Renin – to help detect the overproduction of aldosterone by the adrenal glands (which may be due to a tumor)
Cortisol – to detect an overproduction of cortisol that may be due to Cushing’s syndrome
Catecholamines and Metanephrines – measure epinephrine, norepinephrine, and their metabolites and are used to help detect the presence of a pheochromocytoma that can cause episodes of severe hypertension
Non-Laboratory Tests
Blood pressure measurement
This is the primary tool for detecting and monitoring hypertension. Although it can now be evaluated with a variety of electronic devices, blood pressure is traditionally and most accurately measured with a stethoscope and a blood pressure cuff (a sphygmomanometer – which includes a cuff, a bulb, and a pressure dial that reads the pressure in millimeters of mercury (mm Hg)). The cuff is placed on a patient’s upper arm and a bulb attached to the cuff is squeezed and released several times to inflate the cuff and increase pressure on the arm until the arterial blood flow is temporarily shut off. The person taking the blood pressure listens through the stethoscope (which has been placed over the artery in the patient’s arm) while slowly releasing the air and reducing the pressure in the cuff. The pressure at which the heartbeat can be heard again is the systolic pressure. The pressure at which the sound again disappears is the diastolic pressure. The pressure is given a systolic over diastolic; for instance, 120 over 80 is a systolic pressure of 120 and a diastolic of 80 mm Hg.
Blood pressure measurements are usually performed with the patient sitting quietly for a few minutes but may also be done in other postures, such as standing. If a patient has an elevated blood pressure, the pressure in the other arm may be measured to confirm the finding. Since blood pressure can and will vary, a diagnosis of hypertension is not made from set of measurements, but will involve multiple measurements made at different times. It is not a high reading the doctor is interested in, but persistent high blood pressure.
The doctor may have the patient wear a device that monitors and records the blood pressure at regular intervals during the day to evaluate their blood pressure over time. This is especially helpful during the diagnostic process and can help rule out the high measurements that are sometimes present only when the patient is in the doctor’s office. This is known as the “white coat phenomenon,” which has been estimated to account for as much as10-20% of suspected cases of hypertension. There are now electronic blood pressure measuring devices that can be used in the home. These can be used effectively but should be checked at intervals against the findings at the doctor’s office to ensure accuracy.
These forms of blood pressure measurement are considered indirect. Rarely, a direct measurement of blood pressure may be required. This can be obtained by inserting a catheter into an artery to measure the pressure inside the blood vessel.
As part of the diagnostic process and to help evaluate the status of vital organs, the doctor may order or perform one or more of the following:
ECG (Electrocardiography) – to evaluate the heart rate
Eye Exam – to look at the retina for changes in the blood vessels (retinopathy)
Physical Exam – to help evaluate the kidneys, to look for abdominal tenderness, to listen for bruits (the sound of blood flowing through a narrowed artery), to examine the thyroid gland in the throat for any enlargement or signs of dysfunction, and to detect any other clinical signs as they present
Imaging scans, such as X-ray or ultrasound of the kidneys or X-ray of the chest
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