The "lower limit of normal" for spirometry once more
There can be little doubt that the distribution of lung function indices of healthy subjects and those with lung pathology overlaps. It is therefore risky to conclude that a test result > lower limit of normal (5th percentile) excludes pathology; it goes without saying that clinical judgement matters. On that account it has been suggested that a FEV1/FVC ratio < 0.70 but > lower limit of normal, hence within the normal range and dubbed the “twilight zone”, represents lung pathology. Evidence to support this is lacking. However, if subjects in the “twilight zone” develop respiratory symptoms and signs after a number of years, this might lend support to this claim. Supportive evidence has not been found in longitudinal studies:
GOLD stage 1 (FEV1/FVC < 0.70 & FEV1 > 80% predicted) in asymptomatic subjects is not associated with
• Premature death [1-5]
• Accelerated decline in FEV1, development of respiratory symptoms, increased use of health care, decrease in “quality of life” [6,7].
FEV1/FVC < lower limit of normal is associated with
• Premature death [8,9]
• Development of respiratory symptoms .
Conclusion: The GOLD criterion is unscientific, clinically unfounded, and the use of FEV1/FVC < 0.70 as a criterion for diagnosing airway obstruction should be discouraged in view of under diagnosis in young subjects and extensive over diagnosis in elder adults ; use the lower limit of normal (LLN) instead.
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