At this time, there is no blood test, brain scan, or other lab test to diagnose CFS. The syndrome is diagnosed by exclusion through:
- Documenting the patient's medical history
- Performing a thorough medical examination
- Conducting cognitive function tests
- Ruling out other conditions that may be causing or exacerbating the fatigue (and/or identifying and treating those that can be treated)
- Fulfilling the Centers for Disease Control and Prevention (CDC) criteria for the definition of CFS
- Monitoring the patient over time to see if other underlying conditions arise
Laboratory tests can be useful to help diagnose and manage other conditions with similar symptoms and disorders that must be identified and treated before a diagnosis of CFS can be made. The CDC recommends a few general tests, bulleted in the next section.
- CMP (Comprehensive Metabolic Panel) to examine electrolytes, proteins, liver and kidney function, calcium, and glucose
- CBC (Complete Blood Count) to look for anemia, white and red blood cell abnormalities
- ESR (Erythrocyte Sedimentation Rate), a nonspecific indicator of inflammation
- TSH (Thyroid Stimulating Hormone) and/or other thyroid testing since hypothyroidism can cause symptoms similar to CFS
- Iron studies to look for iron deficiency or abnormalities in iron storage or use
- Urinalysis to look for infections and for sugars, proteins, and waste products that may be excreted in the urine
Other tests may be ordered to follow up abnormal findings on the general tests and as warranted by the affected individual's symptoms. These additional tests are used to help identify or rule out diseases and disorders that may be causing fatigue; they are not capable of directly diagnosing CFS. These may include:
- ANA (Antinuclear Antibodies), ordered when an autoimmune disorder is suspected
- TB skin test to check for exposure to the mycobacterium that causes tuberculosis
- Lyme disease test when suspected and endemic in the patient's geographical area
- Rheumatoid Factor to determine whether rheumatoid arthritis may be present
- HIV antibody test to check for HIV infection
- Cortisol test when low cortisol concentrations and/or decreased adrenal gland function are suspected
Other laboratory tests may be used in a research setting to attempt to better understand the cause and course of CFS.
Occasionally, an MRI (magnetic resonance imaging) scan may be ordered to help rule out multiple sclerosis as a cause of chronic fatigue. Other tests and imaging scans may be used in a research setting but are not considered clinically useful at this time.