A physician seeing a patient who may have chronic fatigue syndrome (CFS) will typically review the patient's medical history and perform a physical examination focusing on the joints, lymph nodes and other body parts affected. Physicians often assess mental status by asking questions or using an oral or written test.

Blood tests and urine tests may be ordered to identify or rule out other possible sources of fatigue, such as anemia (insufficient number of red blood cells). Tests suggested by the U.S. Centers for Disease Control and Prevention (CDC) for screening patients for chronic fatigue syndrome include:

• Complete blood count and electrolytes, to indicate many possible underlying diseases
  
  
• Sedimentation rate, to detect inflammation
  
  
• Waste product tests, to detect kidney disease and other disorders
  
  
• Alanine aminotransferase (ALT) and globulin, to detect liver diseases
  
  
• Albumin, to detect malnutrition, liver disease, kidney disease or other problems
  
  
• Calcium, to detect cancer and other disorders
  
  
• Phosphorus, to detect kidney failure and other disorders
  
  
• Glucose, to detect diabetes
  
  
• Total protein, to detect dehydration
  
  
• Thyroid stimulating hormone (TSH), to detect thyroid disorders
  
  
• Urinalysis, to detect kidney diseases, lupus and many other disorders

More than 90 percent of patients with severe fatigue will have normal results for the above lab tests, according to the CDC.

Depending on the symptoms presented by the individual, imaging tests such as x-rays or CAT scan (computed axial tomography) may also be ordered. The physician may recommend a tilt table test to detect the low blood pressure (neurally mediated hypotension) that some CFS patients have.

Patients must meet two criteria to be diagnosed with chronic fatigue syndrome, according to the U.S. National Institutes of Health (NIH) and international CFS experts:

• Have severe, chronic fatigue for six months for more, with other known causes ruled out by clinical diagnosis
  
  
• Have four or more of the following symptoms for the previous six months or longer:
  
• • Substantially impaired concentration or short-term memory
    
  • Sore throat
    
  • Tenderness in the lymph nodes of the armpits or neck
    
  • Muscle pain
    
  • Multiple joint pains without swelling or redness
    
  • Headaches of a new type, pattern or severity
    
  • Lack of refreshment from sleep
    
  • Discomfort for more than 24 hours after exertion

A diagnosis of CFS is a diagnosis of exclusion, meaning other medical conditions must be ruled out. CFS is diagnosed if there is no other explanation for the fatigue and if the other symptoms did not develop before the fatigue, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS).  Thus diagnosis may be a time-consuming process for the patient and may become frustrating.

It should be noted that some physicians, researchers and facilities may accept a co-diagnosis of CFS in people who have other illnesses that involve chronic fatigue. However, the NIH and other U.S. government health agencies exclude these conditions, unless the condition has been treated adequately and no longer explains the fatigue and other symptoms. The list of conditions includes:

• Fibromyalgia
• Chronic mononucleosis
• Autoimmune diseases such as lupus
• Glandular and hormonal disorders such as hypothyroidism
• Lyme disease
• Cancer
• Sleep apnea and narcolepsy
• Arthritis
• Infections
• Gulf War syndrome
• Chemical sensitivities
• TMJ disorder
• Obesity
• Depression and other mental disorders
• Alcohol and drug abuse
• Reactions to medications

Scientists are trying to develop diagnostic techniques specific to CFS. Spinal taps have revealed a group of proteins found in the cerebrospinal fluid of people with CFS but not in healthy individuals. These findings are not sensitive or specific at this time but could eventually lead to a test that allows earlier diagnosis and treatment.

The CDC advises against trying to diagnose CFS with experimental serologic and immunologic tests, such as retrovirus tests. Testing for Epstein-Barr virus (EBV) was once used in diagnosing chronic fatigue syndrome because EBV was considered a likely cause, but scientists have learned that many cases of CFS have no link to this virus.