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Table 1 Symptoms and related physical signs based on the Canadian Criteria for ME/CFS diagnosis, presented by class, and as assessed at the CFS Discovery Clinic

From: Weighting of orthostatic intolerance time measurements with standing difficulty score stratifies ME/CFS symptom severity and analyte detection

Canadian criteria symptom classes Role in CFS/ME diagnosis Specific symptoms identified Factor analysis (% variance)* ANOVA (p value)**
Post-exertional malaise and fatigue Mandatory Fatigue, malaise and/or pain post effort ≥ 24-h recovery All symptoms are mandatory (100%)#
Minimum 6-months fatigue Mandatory ≥ 6-months unexplained fatigue Symptom mandatory (100%)#
Sleep disorder Mandatory Difficulty going to sleep
Sleep during day
62% (p < 0.0001)
Pain Mandatory Pain (any region)
87% (p < 0.0001)
71% (p = 0.118)
Neurological/cognitive manifestations ≥ 2 criteria required Light, sound and/or smell sensitivity
62% (p < 0.0001)
38% (p < 0.0001)
Breathless 58% (p < 0.0001)
   Arrhythmia 42% (p < 0.0001)
Autonomic/neuroendocrine/immune manifestations ≥ 1 criteria for 2 of the 3 categories required Gut  
Bloating, abdominal pain, diarrhoea 40% (p < 0.0001)
Hot/Cold flushes 73% (p < 0.0001)
Tender glands, flulike symptoms, chemical (allergy) sensitivity 45% (p < 0.0001)
  1. Identification of significant diagnostic criteria responses via factor analysis of a tetrachoric correlation matrix
  2. Based on Canadian Criteria [1]
  3. * Percentage variance explained, derived from factor analysis of tetrachoric correlation matrix across all CFS/ME severity classes, including healthy study controls
  4. ** p values calculated from ANOVA of factor scores across four classes of severity defined by weighted standing time (WST)
  5. #No (0%) healthy controls reported a minimum of 6-months fatigue, or post-exertional fatigue/malaise