CHEST Guidelines-Cut-to-the-Chase

Cut-to-the-Chase_chest
Pdf Summary
The article by Neil R. MacIntyre, MD, and Yuh Chin Huang, MD, discusses the interpretation of pulmonary function tests (PFTs), emphasizing the use of cut-points to differentiate normal from abnormal results. Pulmonary function tests, which include spirometry, lung volume determinations, and diffusing capacity, have been foundational for over a century in assessing respiratory function. These tests help describe physiological parameters, determine abnormal ranges, and suggest diagnostic possibilities.<br /><br />Traditionally, results are compared against predicted values determined by factors like age, sex, and height. Although fixed cut-points, such as an FEV1/FVC ratio of 0.70 for COPD diagnosis, are commonly used due to their simplicity, they are somewhat arbitrary and can be misleading. The authors argue for a statistics-based approach using the lower limit of normal (LLN), defined as below the fifth percentile of predicted values, which accounts for variability in normal and disease states.<br /><br />Severity of impairment is often quantified using percent predicted values, categorized as mild, moderate, or severe, though these cut-points may not be truly discriminatory across all ages. Z scores, which represent deviations from the mean, offer an alternative grading system, providing potentially better alignment with disease states and outcomes. However, studies linking these measures to clinical outcomes have been inconclusive.<br /><br />Vaz Fragoso et al.'s reanalysis of the UPLIFT study highlights the potential benefits of utilizing LLN and z scores for more accurate COPD diagnosis and management, showing improvements in mortality with this approach. Despite the promise of statistically based systems, the article concludes that current practice should continue reporting both percent predicted and z scores to bridge familiarity and functional understanding until further evidence supports one approach's superiority. Professional groups are leaning towards the z score approach, but a combined reporting method remains a practical solution for now.
Keywords
pulmonary function tests
spirometry
lung volume
diffusing capacity
FEV1/FVC ratio
lower limit of normal
percent predicted values
z scores
COPD diagnosis
UPLIFT study