Agreement between fixed-ratio and lower limit of normal spirometry interpretation protocols decreases with age: is there a need for a new GOLD standard?

Objectives: To assess concordance between the fixed 70% ratio cutoff point with the fixed percent predicted values (Fixed-ratio) and the lower limit of normal (LLN) algorithms in interpreting spirometry results in an older population.
Methods: Spirometries were interpreted using Third National Health and Nutrition Examination Survey reference equations for 2319 workers.
Results: The Fixed-ratio algorithm characterized 34.5% (n = 801) results as abnormal, compared with 29.7% (n = 689) by the LLN. There were almost twice as many obstructive and mixed airways spirometries identified under the Fixed-ratio compared to LLN. Rates of restrictive pattern physiology were virtually the same under each algorithm. Overall agreement between the algorithms decreased with age from "almost perfect" for those younger than 60 years to "substantial" for those older than 80 years.
Conclusions: This study found age-related discordance between two algorithms possibly related to the lack of reference equations and standards for individuals older than 80 years.