Diagnosis of Chronic Fatigue Syndrome 

In this section​ you will find information on the following


Diagnosis of CFS


Chronic Fatigue Syndrome (CFS) is a condition of unknown cause. Thus, the diagnosis is made by exclusion of conditions that could cause fatigue in combination with the use of diagnostic criteria. Over the last 25 years, since the interest around CFS has increased, different diagnostic criteria have been created, which share many common features but also have some differences. The most used of these criteria are the CDC criteria, which are described below, along with all the others.

CDC criteria (1994) [1]


The main symptom is unexplained, persistent or recurrent chronic fatigue (equal to or more than six months) that has a new or definite onset, is not the result of continuous effort, there is no substantial relief with rest and results in considerable reduction in occupational, educational, social or personal activities. There must be simultaneous occurrence of four or more symptoms that have persisted or recurred six months or more, but should not have been present before the onset of fatigue. These include:

  1. Cognitive dysfunction, such as reduction of short-term memory or concentration, difficulty with finding words, planning / organizing thoughts and information processing,

  2. painful lymph nodes without pathological enlargement,

  3. sensitive cervical or axillary lymph nodes,

  4. muscle pain,

  5. pain in multiple joints without oedema or redness,

  6. headaches of a new type, pattern or severity,

  7. non-refreshing sleep,

  8. fatigue or malaise after physical effort, which often occurs with a delay, perhaps after 24 hours and lasts longer than 24 hours.


Oxford criteria (1991) [2]


Fatigue has a definite beginning, is severe, disabling and affects the physical and mental functioning. It must be present for at least six months and be displayed for more than 50% of the time duration of the disease. Associated symptoms are in particular myalgia, mood and sleep disturbances. CFS is excluded if there are medical conditions that produce chronic fatigue (e.g. severe anaemia) and in the cases of mental illness: schizophrenia, manic depression, substance abuse, eating disorders or proven organic brain disease. CFS is not excluded in psychiatric disorders such as depression, anxiety disorders and hyperventilation syndrome.


Revised criteria of Canada (2010) [3]


The main symptom is recurrent or persistent chronic fatigue that is life-long and leads to reduced activity. There is simultaneous appearance of continuous or recurrent symptoms, which may be present before the onset of the fatigue, such as:


  1. loss of physical or mental endurance,

  2. rapid / sudden muscle or cognitive fatigue, malaise and / or fatigue after effort and tendency of associated symptoms aggravation,

  3. sleep disorders,

  4. widespread, often immigrant, pain (or discomfort) such as myofascial, muscular, articular (without oedema), abdominal, headache,

  5. two or more neurological / cognitive manifestations, such as problems with memory, vision, attention, perception, speech, mind, thought, expression, information processing,

  6. sensitivity to noise / lights, muscle weakness / muscle contractions.


There is at least one symptom in two of three categories:

  1. Autonomous: neural hypotension, orthostatic tachycardia, delayed postural hypotension, palpitations with or without cardiac arrhythmia, dizziness or fainting, feeling of instability - impaired balance, shortness of breath, nausea, bladder dysfunction or irritable bowel syndrome,

  2. Neuroendocrine: fever and feeling of cold extremities, reduced temperature and marked daily variations, sweating, intolerance to extreme heat and cold, significant weight change, loss of appetite or abnormal appetite,

  3. Immune: recurring influenza symptoms, non-productive sore or itchy throat, repeated fevers and sweats, lymph nodes sensitive to palpation, new sensitivities to food, odours, or chemicals.

  4. CFS is excluded if there is any active medical condition explaining chronic fatigue, and in some active psychiatric diseases such as:

             a) schizophrenia or psychotic disorders, bipolar disorder,

             b) cases of alcohol or substance abuse,

             c) active anorexia or bulimia nervosa,

             d) depression with melancholic or psychotic features.

CFS is not excluded in the case of therapeutic solving of the abuse and in disorders that do not explain the fatigue, such as stress, or that cannot be confirmed diagnostically, such as fibromyalgia.

ME-ICC criteria (2011) [4]


The disease is called Myalgic Encephalomyelitis and there is no need for it to be present for six months before a diagnosis can be made. A patient must meet the criteria for exhaustion after effort of the neuro-immune system and must have:

  1. at least one symptom from three categories of neurological dysfunction: neurocognitive disorders, pain, sleep disorders, neurosensory, movement disorders and cognitive disorders,

  2. at least one symptom from the three categories of failure of the immune / gastro-intestinal / genitourinary: flu symptoms, susceptibility to viral infections, gastrointestinal tract, urogenital, sensitivity to foods, drugs, substances and

  3. at least one symptom from the metabolism of energy: cardiovascular, such as hypotension, respiratory, such as difficulty with breathing, thermoregulation loss, intolerance to extreme temperature. The severity of the symptoms leads to a significant reduction of activities.


Revised criteria of London (2014) [5]


Five criteria must be met:   

  1. significant muscle fatigue / weakness after little activity,

  2. symptoms from the central nervous system such as memory disorders, concentration, sleep, balance problems,

  3. periods of the autonomic system problems such as facial pallor, thermoregulation disorders, hypotension,

  4. variation of symptoms during the day and

  5. symptoms to appear within the last 3 months.


IOM criteria (2015) [6]


The disease is called "Systemic Exertion Intolerance Disease” (SEID). The essential symptoms are:

  1. reduced level of activity for six months with simultaneous fatigue for at least half of the time, with new or definite onset that is not the result of excessive effort and does not sooth with rest,

  2. malaise after the effort,

  3. non-refreshing sleep.

At least one symptom of cognitive dysfunction or orthostatic hypotension is required. Other symptoms include pain, immune dysfunction and infections. Gastrointestinal disorders, genitourinary disorders, sore throat, painful lymph nodes, sensitivity to foods, drugs and substances can occur less often.


Laboratory tests


A series of tests must be done in order to exclude any other causes for the presence of chronic fatigue. These tests are listed in the table below.















    Table of lab tests to diagnose CFS




  1. Fukuda et al, and the International Chronic Fatigue Syndrome Study Group. The Chronic Fatigue Syndrome: A Comprehensive Approach to Its Definition and Study. Ann Intern Med. 1994;121:953-959.

  2. Sharpe et al. A report - chronic fatigue syndrome: guidelines for research. J of the Royal Soc Medic 1991;84,118-122.

  3. Jason et al. The Development of a Revised Canadian Myalgic Encephalomyelitis Chronic Fatigue Syndrome Case Definition. Am J of Biochem and Biotech 2010;6 (2):120-135.

  4. Carruthers et al. Myalgic encephalomyelitis: International Consensus Criteria. J Intern Med 2011;270:327–338.

  5. Howes et al. Myalgic Encephalomyelitis (ME). Criteria and clinical guidelines 2014.

  6. Clayton et al. Beyond Myalgic Engephalomyelitis / Chronic Fatigue Syndrome. Redefining and illness. Report guide for clinicians. The National Academy Press 2015 Washington D.C.