Comparison of apnoea–hypopnoea index and oxygen desaturation index when identifying obstructive sleep apnoea using type‐4 sleep studies

Summary The concordance of different indices from type‐4 sleep studies in diagnosing and categorising the severity of obstructive sleep apnoea is not known. This is a critical gap as type‐4 sleep studies are used to diagnose obstructive sleep apnoea in some settings. Therefore, we aimed to determine the concordance between flow‐based apnoea–hypopnoea index ( AHI flow50% ) and oxygen desaturation index ( ODI 3% ) by measuring them concurrently. Using a random sub‐sample of 296 from a population‐based cohort who underwent two‐channel type‐4 sleep studies, we assessed the concordance between AHI flow50% and ODI 3% . We compared the prevalence of obstructive sleep apnoea of various severities as identified by the two methods, and determined their concordance using coefficient Kappa(κ). Participants were aged (mean ± SD) 53 ± 0.9 years (48% male). The body mass index was 28.8 ± 5.2 kg m −2 and neck circumference was 37.4 ± 3.9 cm. The median AHI flow50% was 5 (inter‐quartile range 2, 10) and median ODI 3% was 9 (inter‐quartile range 4, 15). The o bstructive sleep apnoea prevalence reported using AHI flow50% was significantly lower than that reported using ODI 3% at all severity thresholds. Although 90% of those with moderate–severe obstructive sleep apnoea classified using AHI flow50% were identified by using ODI 3% , only 46% of those with moderate–severe obstructive sleep apnoea classified using ODI 3% were identified by AHI flow50% . The overall concordance between AHI flow50% and ODI 3% in diagnosing and classifying the severity of obstructive sleep apnoea was only fair (κ = 0.32), better for males (κ = 0.42 [95% confidence interval 0.32–0.57] versus 0.22 [95% confidence interval 0.09–0.31]), and lowest for those with a body mass index ≥ 35 (κ = 0.11). In conclusion, ODI 3% and AHI flow50% from type‐4 sleep studies are at least moderately discordant. Until further evidence is available, the use of ODI 3% as the measure of choice for type‐4 sleep studies is recommended cautiously.