Some Causes and Features of Fainting
Cause | Common Features* | Tests† |
|---|---|---|
Serious causes | ||
Heart valve disorders, such as aortic stenosis, mitral stenosis, or failure of an artificial heart valve Cardiomyopathy (disorders affecting heart muscle), particularly hypertrophic cardiomyopathy | Fainting during or after exercise, followed by a prompt recovery In young or old people Often in people who are known to have had a heart murmur | Echocardiography (ultrasonography of the heart) |
A very slow heart rate (typically less than 35 beats per minute), more common in older people A very rapid heart rate (typically over 150 beats per minute) | Fainting without warning, followed by recovery immediately after awakening Fainting that may occur in any position Sometimes in people taking certain drugs, especially drugs used to treat heart disorders such as abnormal heart rhythms (antiarrhythmic drugs) | ECG, sometimes continuous ambulatory ECG (using a Holter monitor or longer recording with an event monitor) Sometimes blood tests to measure electrolytes such as sodium and potassium |
Pulmonary embolism (blockage of an artery to the lungs by a blood clot) | Often sharp pain when breathing in, shortness of breath, rapid breathing, and a rapid heart rate Sometimes mild fever, coughing up blood, or shock More likely in people with risk factors for pulmonary embolism (such as previous blood clots, recent surgery especially surgery on the legs, prolonged bed rest, a cast or splint on a leg, older age, smoking, or cancer) | CT angiography or nuclear scanning of the lungs Sometimes a blood test to detect blood clots (D-dimer test) |
Heart attack (myocardial infarction) | Usually in older people Usually chest discomfort, feeling of indigestion, shortness of breath, or nausea | ECG Blood tests to measure substances that indicate heart damage (cardiac markers) |
A severe allergic reaction (anaphylaxis) causing very low blood pressure | Fainting during or shortly after being exposed to a trigger for an allergic reaction, such as a drug or an insect bite Excessive sweating and pale skin color In people who may or may not have a history of allergies Usually hives, wheezing, or swelling of part of the body (called angioneurotic edema) | Allergy testing |
A low blood sugar level (hypoglycemia) | Fainting after a period of other symptoms, including confusion, shakiness, and sweating Unresponsiveness or confusion that remains until people are treated Almost always in people with diabetes | Fingerstick glucose measurement Immediate recovery following glucose infusion |
Less serious causes | ||
Increased pressure in the chest (for example, due to coughing or straining during urination or a bowel movement) | Fainting during an activity that increases pressure in the chest Warning symptoms (for example, dizziness, nausea, or sweating) Recovery that is prompt but not immediate (within 5 to 15 minutes, but the person may feel unwell for several hours) | Only a doctor's examination |
Strong emotion (such as pain, fear, or distress at the sight of blood) | Fainting when experiencing strong emotion Warning symptoms (for example, dizziness, nausea, or sweating) Recovery that is prompt but not immediate (within 5 to 15 minutes) A cause that is usually apparent | Only a doctor's examination |
Fainting sometimes preceded by disturbances in sensation, vision, or other functions (called the aura) Throbbing headache, often on one side of the head Sensitivity to light and/or sounds | Only a doctor's examination | |
Standing for a long time | A cause that is apparent based on the history No other symptoms | Only a doctor's examination |
Pregnancy | In healthy women of childbearing age No other symptoms Usually in women with an early or unrecognized pregnancy | Urine pregnancy test |
Hyperventilation | Often tingling around the mouth or in the fingers before fainting Usually during or in response to an emotional situation Rapid breathing, which may not be noticed by the person or by others Typically in younger people | Only a doctor's examination |
Drugs used to lower the blood pressure (but rarely beta-blockers), such as loop diuretics and nitrates | Light-headedness, followed by fainting within several minutes of sitting up or standing A drop in blood pressure when standing, detected during the examination | A doctor's examination Sometimes tilt table testing |
Drugs that can cause irregular and rapid heart rate by affecting the heart's electric activity such as antipsychotics (mainly phenothiazines), some antiarrhythmic drugs, some antidepressants, and some antibiotics | Sometimes palpitations and light-headedness Sudden loss of consciousness | A doctor's examination ECG |
Malfunction of the autonomic nervous system (which regulates internal body processes that require no conscious effort, such as blood pressure) | Light-headedness, followed by fainting within several minutes of sitting up or standing A drop in blood pressure when standing, detected during the examination | A doctor's examination Sometimes tilt table testing |
Deconditioning caused by bed rest for many days | Light-headedness, followed by fainting within several minutes of sitting up or standing A drop in blood pressure when standing, detected during the examination | A doctor's examination Sometimes tilt table testing |
Anemia | Light-headedness, followed by fainting within several minutes of sitting up or standing Chronic fatigue Sometimes dark stools or heavy menstrual periods | A complete blood count Stool tests to check for blood |
* A doctor's examination is always done. Features include symptoms and the results of the doctor's examination. Features mentioned are typical but not always present. | ||
† In all people who have fainted, ECG is done, and oxygen levels in the blood may be measured with a sensor placed on a finger (pulse oximetry). | ||
CT = computed tomography; ECG = electrocardiography; MRI = magnetic resonance imaging. | ||