Chronic Fatigue Syndrome (CFS) Workup

Updated: May 19, 2017
  • Author: Burke A Cunha, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Laboratory Studies

Laboratory tests have 2 functions in chronic fatigue syndrome (CFS). First, they may be used to assess the possibility that another condition is causing the fatigue; second, they may be used to help diagnose CFS. CFS laboratory abnormalities are not specific, but, taken together, they can make up a pattern consistent with CFS in patients who have a cognitive dysfunction in whom other diseases have been excluded as a cause for their fatigue.

The Centers for Disease Control and Prevention (CDC) has recommended a “basic battery” that includes the following:

  • Complete blood count (CBC)
  • Liver function tests
  • Thyroid function tests
  • Erythrocyte sedimentation rate (ESR)
  • Serum electrolyte level measurement

Some clinicians also include antinuclear antibody and morning cortisol measurements. Adrenal function tests are useful for the purposes of exclusion.

The most consistent laboratory abnormality in patients with CFS is an extremely low ESR, typically in the range of 0-3 mm/h. An normal ESR or one that is in the upper reference range suggests another diagnosis.

Most patients with CFS usually have 2 or 3 of the following nonspecific abnormalities:

  • Elevated immunoglobulin M (IgM)/immunoglobulin G (IgG) coxsackievirus B titer
  • Elevated IgM/IgG human herpesvirus 6 (HHV-6) titer
  • Elevated IgM/IgG C pneumoniae titer
  • Decrease in natural killer (NK) cells (either percentage or activity)

The WBC count in patients with CFS is normal. Leukopenia, leukocytosis, or an abnormal cell differential count indicates a diagnosis other than CFS, and another cause should be pursued to explain these findings.

Results of liver function tests are within the reference range in patients with CFS. Increased levels of serum transaminases, alkaline phosphatase, or lactic dehydrogenase should prompt a search for another explanation because these values are typically normal CFS.

Serum protein electrophoresis is normal in patients with CFS but may be used to rule out other diseases that cause fatigue, including lymphoma and myeloma.

Urinalysis findings are unremarkable in CFS.


Other Tests

CT, MRI, and PET

Computed tomography (CT) or magnetic resonance imaging (MRI) of the brain is useful for ruling out central nervous system (CNS) disorders in patients with otherwise unexplained CNS symptoms. Results of CT scans and MRI may be normal in patients with CFS. Findings of CNS imaging studies are not specific for CFS and are thus used to rule out alternative explanations rather than to diagnose CFS.

Positron emission tomography (PET) shows hypoperfusion in the frontoparietal/temporal region.