Impact of different criteria for defining hypopneas in the apnea-hypopnea index.

OBJECTIVES: To explore the effect of using different scoring criteria for hypopneas in the scoring of polysomnographic studies: (1) by estimating the level of agreement between apnea-hypopnea index (AHI) scores derived from different scoring methods, and (2) by examining the effect on the point prevalence of disease using different threshold values of the AHI.
DESIGN: Retrospective analysis of 48 diagnostic polysomnographic records.
SETTING: Tertiary-hospital sleep-disorders clinic. MEASUREMENTS: AHIs were derived from three different methods for scoring hypopneas. The hypopnea definitions used incorporated different combinations and threshold values of respiratory signal changes in addition to differences in the requirement for associated oxygen desaturation or arousal. The level of agreement between different scoring methods was assessed by constructing Bland-Altman plots and calculating intraclass correlation coefficients (ICCs). kappa statistics were used to assess agreement between the different methods using varying thresholds of AHI to categorize sleep apnea (AHI > 5, AHI > 15, and AHI > 20).
RESULTS: The random-effects ICC for the three methods was 0.89, suggesting that the different scoring methods tended to rank patients fairly consistently. However, the point prevalence of disease estimated by using different thresholds of AHI was found to vary depending on the method used to score sleep studies (kappa, 0.30 to 0.95).
CONCLUSIONS: These findings have implications for case finding, population-prevalence estimates, and grading of disease severity for access to government-funded continuous positive airway pressure services. Guidelines for standardizing the measurement and reporting of sleep studies in clinical practice should be implemented.