II. Background: Three different staging systems

  1. Global Initiative for Chronic Obstructive Lung Disease (GOLD)
  2. American Thoracic Society (ATS) and European Respiratory Society (ERS)
  3. British Thoracic Society (BTS)

III. Criteria

  1. Stage 0 - at risk (ATS/ERS)
  2. FEV1 to FVC ratio: >0.7
    1. FEV1 >79% of predicted: Stage 0 - at risk (ATS/ERS): Symptomatic Smokers
  3. FEV1 to FVC ratio <0.7
    1. FEV1 >79% of predicted: Stage 1 - Mild (GOLD, ATS/ERS)
    2. FEV1 50-80% of predicted: Stage 2 - Moderate (GOLD, ATS/ERS), (BTS-Stage 1)
    3. FEV1 30-49% of predicted: Stage 3 - Severe (GOLD, ATS/ERS), (BTS-Stage 2)
    4. FEV1 <30% of predicted: Stage 4 - Very Severe (GOLD, ATS/ERS), (BTS-Stage 3)

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