The most important step for a physician in diagnosing syncope is to collect a medical history, followed by a physical examination. During the history, patients should be detailed about the fainting episode and include information about any previous episodes of fainting. It is also important to let the physician know about any medical conditions.

This information will help the physician decide what further tests should be ordered. A slower onset of fainting spells with prolonged or pronounced warning signals may indicate a metabolic problem, whereas a sudden incident points more to potential cardiac or circulatory problems. Whatever the cause, the physician will diagnose it as soon as possible so that potentially life-threatening conditions can be treated or avoided.

To make a diagnosis, the physician may order a number of tests. In patients with diabetes, a glucose test may be administered because low glucose (blood sugar) is a common cause of fainting in people with diabetes.

Another cause of fainting in people with diabetes is related to the autonomic nervous system. Tests used to diagnose autonomic neuropathy include nerve conduction velocity and electromyography.

Other tests that may be ordered include:

• Tilt table test. This test is used to assess a sudden drop in blood pressure with a widening of the blood vessels. Fainting that results from this change in blood pressure and blood vessels is called neurocardiogenic syncope. The tilt table test is conducted on a pivoting table. By securing the patient on his or her back to the tilt table, and then tilting the table upright, the factors leading to neurocardiogenic syncope may be simulated.
  
  
• Echocardiogram. This type of ultrasound uses sound waves to visualize the structures and functions of the heart. A moving image of the patient’s beating heart is played on a video screen, where a physician can study the heart’s thickness, size and function. It may reveal underlying cardiac conditions that could be causing the patient to faint.
  
  
• Holter monitor. This is an electrocardiogram (EKG) that is attached to a patient for 24 hours. It continuously records the heart’s electrical activity as the patient goes about the daily routine. Because of the relative rarity of fainting, this approach frequently fails to yield useful information.
  
  
• Event monitor. If a patient experiences symptoms only rarely, the Holter monitor may not pick up the pattern and thus may not alert the physician to the problem. The physician may therefore ask the patient to carry a different type of portable device called an event recorder or event monitor. Rather than monitoring the heart’s electrical activity continuously (as the Holter monitor does), an event recorder is used only when the patient is feeling symptoms. When symptoms occur, the patient activates the event recorder by pressing a button. Because these devices are “on-demand” rather than continuous, these recorders may be used for weeks or months. In certain cases, they may better reveal the pattern of symptoms.
  
  
• Electrophysiologic study. A thin tube (catheter) is inserted into a vein or artery (e.g., in the groin) and guided to the heart, where it can perform specific, essential measurements of the heart’s electrical activity and pathways. These measurements are particularly helpful in the diagnosis of heart rhythms that are particularly fast (tachycardias) or slow (bradycardias).
  
  
• CAT scan (computed axial tomography). Multiple x-rays are taken of the brain from a variety of angles. A computer is used to reassemble the views into cross–sectional images. It can provide clearer, more detailed information than single x-rays and can be used on a variety of tissues, including soft tissue, bone and blood vessels.
  
  
• MRI (magnetic resonance imaging). Magnetic fields and a computer produce high-resolution cross-sectional or three-dimensional images of the brain, heart and other structures. Images from an MRI scan are similar in many ways to those of a CAT scan, but MRI generally provides greater contrast between normal and abnormal tissues. It is done without x-rays or other forms of radiation.
  
  
• Electroencephalogram (EEG). A test that measures the brain’s electrical activity. It may be used to diagnose epilepsy, head injuries, infections, sleep disorders and other problems.