How is low blood pressure diagnosed and evaluated?

In some individuals, particularly relatively healthy ones, symptoms of weakness, dizziness, and fainting raise the suspicion of low blood pressure. In others, an event often associated with low blood pressure, for example a heart attack has occurred to cause the symptoms.

Measuring blood pressure, sometimes in both the lying (supine) and standing positions usually is the first step in diagnosing low blood pressure. In patients with symptomatic low blood pressure, there often is a marked drop in blood pressure upon standing, and patients may even develop orthostatic symptoms. The heart rate often increases greatly. Once low blood pressure has been identified as the cause of symptoms, the goal is to identify the cause of the low blood pressure. Sometimes the causes are readily apparent (such as loss of blood due to trauma, or sudden shock after receiving x-ray dyes containing iodine). At other times, the cause may be identified by testing:

• CBC (complete blood count). CBC may reveal anemia from blood loss or elevated white blood cells due to infection.

• Blood electrolyte measurements may show dehydration and mineral depletion, renal failure (kidney failure), or acidosis (excess acid in the blood).

• Cortisol levels can be measured to diagnose adrenal insufficiency and Addison's disease.

• Blood and urine cultures can be performed to diagnose septicemia and bladder infections, respectively.

• Radiology studies, such as chest x-rays, abdominal ultrasounds, and computerized tomography (CT or CAT) scans may detect pneumonia, heart failure, gallstones, pancreatitis, and diverticulitis.

• Electrocardiograms (EKG) can detect abnormally slow or rapid heart beats, pericarditis, and heart muscle damage from either previous heart attacks or a reduced supply of blood to the heart muscle that has not yet caused a heart attack.

• Holter monitor recordings are used to diagnose intermittent episodes of abnormal heart rhythms. If abnormal rhythms occur intermittently, a standard EKG performed at the time of a visit to the doctor's office may not show the abnormal rhythm. A Holter monitor is a continuous recording of the heart's rhythm for 24 hours that often is used to diagnose intermittent episodes of bradycardia or tachycardia.

• Patient-activated event recorder. If the episodes of bradycardia or tachycardia are infrequent, a 24-hour Holter recording may not capture these sporadic episodes. In this situation, a patient can wear a patient-activated event recorder for up to four weeks. The patient presses a button to start the recording when he or she senses the onset of an abnormal heart rhythm or symptoms possibly caused by low blood pressure. The doctor then analyzes the recordings at a later date to identify the abnormal episodes.

• Echocardiograms are examinations of the structures and motion of the heart using ultrasound. Echocardiograms can detect pericardial fluid due to pericarditis, the extent of heart muscle damage from heart attacks, diseases of the heart valves, and rare tumors of the heart.

• Ultrasound examinations of the leg veins and CT scans of the chest can detect deep vein thrombosis and pulmonary embolism.

• Tilt-Table tests are used to evaluate patients suspected of having postural hypotension or syncope due to abnormal autonomic nerves. During a tilt-table test, the patient lies on an examining table with an intravenous infusion administered while the heart rate and blood pressure are monitored. The table then is tilted upright for 15 minutes to 45 minutes. Heart rate and blood pressure are monitored every few minutes. The purpose of the test is to try to reproduce postural hypotension. Sometimes a doctor may administer epinephrine (Adrenalin, Isuprel) intravenously to induce postural hypotension.