Cause |
Common Features* |
Tests |
Blood disorders or cancers |
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Decreased exercise tolerance with shortness of breath during activity greater than expected for the activity Sometimes paleness |
CBC |
|
Cancers (such as digestive tract cancer, lung cancer, leukemia, lymphoma, multiple myeloma) |
Widespread lymph node swelling, weight loss, and night sweats With multiple myeloma, low back or other bone pain, often severe at night |
CBC |
Infections |
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Sometimes jaundice, loss of appetite, and fluid in the abdomen |
Blood tests to determine how well the liver is functioning and to identify the hepatitis virus Sometimes liver biopsy |
|
Enlarged spleen and lymph nodes, fever, and night sweats |
Sometimes blood tests for antibodies to cytomegalovirus |
|
Heart valve infection (endocarditis) |
Fever and night sweats Sometimes joint pains Usually in people who have heart murmurs or inject drugs intravenously |
Cultures of blood samples and echocardiography |
Fever, night sweats, and frequent infections Sometimes difficulty breathing, cough, diarrhea, and/or rash |
HIV blood test |
|
Recent sore throat and lymph node swelling |
Mononucleosis blood test |
|
Other infections (for example, fungal pneumonias such as histoplasmosis, parasitic infections, or tuberculosis) |
Fever, night sweats, and weight loss Sometimes cough, difficulty breathing, and coughing up blood |
Tests based on which type of infection seems likely |
Other disorders and causes |
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Shortness of breath, difficulty breathing when lying down that is relieved when upright (orthopnea), and/or swelling |
Blood tests of kidney function |
|
Connective tissue disorder (for example, rheumatoid arthritis or systemic lupus erythematosus [lupus]) |
Fever, night sweats, weight loss, joint pain, rash, and/or other organ involvement (for example, effects on the heart or lungs) |
Blood tests for abnormal antibodies |
Deconditioning |
A history of lack of exercise or being bedbound or hospitalized |
Only a doctor's examination |
Diabetes (sometimes, other symptoms often more prominent) |
Excessive thirst, excessive urination, increased appetite, and unexplained weight gain or loss |
Measurement of sugar (glucose) level in the blood after the person fasts overnight and sometimes glucose tolerance testing |
Drugs: Antidepressants, older antihistamines, antihypertensives, diuretics that cause low potassium levels in the blood, muscle relaxants, recreational drugs, and sedatives |
History of taking a drug known to cause fatigue |
Only a doctor's examination |
Headache, pain in the jaw when chewing, pain when combing hair, loss of vision, and/or muscle pains in a person over 50 |
ESR and temporal artery biopsy |
|
Mental health disorders: Anxiety, depression, drug addiction, panic disorder, or somatization disorder (physical symptoms caused mainly by anxiety) |
Anxiety, sadness, loss of appetite, and unexplained sleep disturbance With somatization disorder, an excessive preoccupation with physical symptoms |
Only a doctor's examination |
Fatigue worse with exposure to heat Past symptoms of nervous system malfunction (such as numbness, loss of coordination, and weakness), particularly if people had more than one episode of symptoms |
Brain and/or spinal cord MRI |
|
Pregnancy |
Cessation of menstrual periods, breast tenderness, morning sickness, and abdominal swelling |
Pregnancy test |
Excessive daytime sleepiness, frequent awakenings, breathing interruptions during sleep, difficulty falling asleep, unrefreshing sleep |
Sleep laboratory testing (polysomnography) |
|
Underactive thyroid gland (hypothyroidism) |
Inability to tolerate cold, weight gain, constipation, and coarse skin |
Blood tests of thyroid function |
Weight loss Sometimes loss of appetite, foul-smelling stool, abdominal pain, or a combination |
A doctor's examination Sometimes other tests |
|
Disorders of unknown cause |
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Chronic fatigue syndrome (now sometimes called myalgic encephalomyelitis or systemic exertion intolerance) |
Sore throat, sleep that is not refreshing, difficulty with concentration or short-term memory, muscle aches, joint pain, headaches, and/or tender lymph nodes in the neck or under the arms |
Only a doctor's examination |
Long-standing and widespread muscle and bone pain in areas outside the joints, trigger points, lower abdominal pain, gas, bloating, constipation or diarrhea, migraines, and anxiety |
Only a doctor's examination |
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*Features include symptoms and the results of the doctor's examination. Features mentioned are typical but not always present. |
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CBC = complete blood count; ESR = erythrocyte sedimentation rate; HIV = human immunodeficiency virus; MRI = magnetic resonance imaging. |