- Severity of Disease: A best AM FEV1 of 50% to 80% of the predicted value during Visit 1 based on the "Standardization of Lung Function Tests" [European Respiratory Society, 1993] standards for 18 years and older or Polgar [Polgar, 1971] standards for 12 to 17 years and race adjusted for African-Americans [American Thoracic Society, 1991].