Diagnostic Criteria for Chronic Fatigue Syndrome (ME/CFS)

Core Diagnostic Requirements

The American College of Cardiology notes that substantial impairment is characterized by a significant reduction in ability to engage in pre-illness occupational, educational, social, or personal activities lasting for at least 6 months 1, 2
Profound fatigue is defined as new or definite onset fatigue that is not substantially alleviated by rest, according to the American College of Cardiology 2, 3
Postexertional malaise is a worsening of symptoms following physical or cognitive exertion, often delayed by hours or days, as noted by the American College of Cardiology 1, 2
Unrefreshing sleep is sleep that does not restore normal energy or function, as described by the American College of Cardiology 1, 3
Cognitive impairment, including problems with memory, concentration, and information processing, is a key symptom, according to the American College of Cardiology 1, 2
Orthostatic intolerance, characterized by symptoms that worsen upon assuming and maintaining upright posture, is also a key symptom, as noted by the American College of Cardiology 1, 2

The clinical evaluation process for ME/CFS involves exclusion of alternative diagnoses, requiring thorough evaluation to rule out other conditions that could explain symptoms, as recommended by the American College of Cardiology 2, 3
A duration requirement of at least 6 months is necessary to meet diagnostic criteria, according to the American College of Cardiology 1, 3
The symptom pattern typically follows a viral or bacterial infection in many cases, as noted by the American College of Cardiology 1, 2
Severity assessment is crucial, with 25% of patients having severe ME/CFS, often meaning they are bed-bound with extreme sensory sensitivity, as described by the American College of Cardiology 1

Immune system abnormalities, including diminished natural killer cell function and T cell exhaustion, are common in ME/CFS patients, as noted by the American College of Cardiology 1
Mitochondrial dysfunction, characterized by impaired energy production and metabolic abnormalities, is also a key finding, according to the American College of Cardiology 1, 4
Vascular and endothelial abnormalities, including deformed red blood cells and reduced blood volume, are associated with ME/CFS, as described by the American College of Cardiology 1
Neurological abnormalities, such as neuroinflammation, reduced cerebral blood flow, and brainstem abnormalities, are common in ME/CFS patients, as noted by the American College of Cardiology 1, 5
Endocrine abnormalities, including hypothalamus-pituitary-adrenal axis dysfunction and low cortisol levels, are also associated with ME/CFS, as described by the American College of Cardiology 1, 5

Misattribution to deconditioning is a common pitfall, as ME/CFS involves complex pathophysiology beyond simple deconditioning, as noted by the American College of Cardiology 1, 3
Overlooking postexertional malaise is a key mistake, as this symptom distinguishes ME/CFS from other fatigue conditions, according to the American College of Cardiology 1, 3
Misdiagnosis as a psychiatric disorder is also a common error, as ME/CFS is a biological illness with neurological and immunological components, as described by the American College of Cardiology 1, 2

Postural Orthostatic Tachycardia Syndrome (POTS) is characterized by a heart rate increase ≥30 bpm within 10 minutes of standing without hypotension, as noted by the American College of Cardiology 2
Long COVID is associated with similar pathophysiological mechanisms as ME/CFS, with about half of long COVID patients meeting criteria for ME/CFS, according to the American College of Cardiology 1

The American College of Cardiology acknowledges that ME/CFS is not comprehensively taught in medical schools, resulting in only 6% of medical schools fully covering ME/CFS across treatment, research, and curricula domains, leading to a significant gap in diagnostic capability 6, 7
ME/CFS and dysautonomia are frequently absent from electronic health record data due to imperfect coding and lack of clinician recognition, highlighting the need for improved diagnostic tools and education 6, 8
The widespread lack of knowledge of viral-onset illnesses prevents these conditions from being identified and documented by clinicians, emphasizing the importance of education and training for healthcare professionals 8

Clinicians should recognize the overlap between ME/CFS and conditions like POTS, where four in five patients receive a psychiatric diagnosis before receiving their correct POTS diagnosis, highlighting the need for careful evaluation and diagnosis 6, 8
The use of inappropriate testing, such as D-dimer, CRP, and antinuclear antibody tests, can lead to misdiagnosis, whereas tests that detect abnormalities in ME/CFS patients, like natural killer cell function tests, tilt table testing, and small fiber neuropathy biopsy, can aid in accurate diagnosis 6

Professional societies and government agencies must educate the healthcare workforce on ME/CFS, including the history and current best practices, to ensure people can receive adequate care now, as recommended by the American College of Cardiology 7
Patients should seek clinicians who have specific training or experience with ME/CFS, dysautonomia, and post-viral conditions, and understand the importance of exclusion of alternative diagnoses through thorough evaluation 6, 7