Comparison of the Lower Confidence Limit to the Fixed-Percentage Method for Assessing Airway Obstruction in Routine Clinical Practice

Abstract

BACKGROUND: Although the statistically derived lower limit of normal (LLN) for the ratio of FEV 1 to FVC is considered superior to a fixed cutoff value (such as 0.70) for diagnosing airway obstruction, the fixed-cutoff method continues to be used and advocated. OBJECTIVE: To evaluate the misclassification of spirometrically determined airway obstruction arising from the use of the fixed-percent method, in comparison to the LLN method for FEV 1 /FVC. METHODS: We reviewed 27,307 spirometry records from adult men, and diagnosed airway obstruction based on the LLN (predicted value minus 1.645 times the standard error of estimate from a north Indian reference equation for FEV 1 /FVC) and based on a fixed cutoff of 0.70. We computed agreement and discordance between the two methods, and determined the sensitivity, specificity, and predictive values of the fixed-percent method in identifying true obstruction. RESULTS: The results were discordant in 1,622 subjects (6%). Overall agreement between the two methods was good (kappa estimate 0.869), but worsened considerably with advancing age. 1,290 subjects (5%) who were deemed normal with the LLN method were diagnosed as having airway obstruction with the fixed-percentage method. Overall the sensitivity, specificity, and positive predictive value of the fixed-percentage method were 0.963, 0.929, and 0.871, respectively. Specificity and positive predictive value decreased sharply with advancing age. CONCLUSIONS: The negative age-dependence of FEV 1 /FVC results in over-diagnosis of airway obstruction in middle-aged and elderly men, and under-diagnosis in young men, with the fixed-percentage method. Airway obstruction should be assessed with the LLN of FEV 1 / FVC, with the LLN derived from appropriate reference equations.

Guidelines for diagnosis and management of chronic obstructive pulmonary disease: Joint ICS/NCCP (I) recommendations

“…[87] Further, discordance between the two methods in classifying obstruction increases in the elderly as LLN values decrease with advancing age. [88] Thus, elderly individuals having a FEV 1 /FVC value which might be within a statistically normal range for their age and gender, face the risk of being diagnosed as having COPD by using FR 0.7 .…”

Serum cytokine profiling and enrichment analysis reveal the involvement of immunological and inflammatory pathways in stable patients with chronic obstructive pulmonary disease

“…These tests are also used for evaluating the treatment efficacy in COPD patients. However, the test results do not fully reflect the burden of COPD 6,7. Aaron et al have studied 19 serum markers and found that only C-reactive protein, myeloperoxidase, and vascular endothelial growth factor show intra- and interpatient reliability and correlation with disease severity 8.…”

Incidence of chronic obstructive pulmonary disease based on three spirometric diagnostic criteria in Sao Paulo, Brazil: a nine-year follow-up since the PLATINO prevalence study

“…[25][26][27] These diagnostic criteria present different sensitivities, specificities and positive and negative predictive values. 23,24,28,29 Although the positive and negative points of each COPD diagnostic criterion have been identified, the historical divergences regarding the use of fixed ratios, LLN, and other criteria still remain in the literature. 30,31 Therefore, further studies that aim to identify the diagnostic and prognostic markers of this disease are needed.…”