Abstract:
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 (AHIflow50%) and oxygen desaturation index (ODI3%) 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
AHIflow50% and ODI3%. 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 AHIflow50% was 5 (inter‐quartile range 2, 10) and median ODI3%
was 9 (inter‐quartile range 4, 15). The obstructive sleep apnoea prevalence reported
using AHIflow50% was significantly lower than that reported using ODI3% at all severity
thresholds. Although 90% of those with moderate–severe obstructive sleep apnoea
classified using AHIflow50% were identified by using ODI3%, only 46% of those with
moderate–severe obstructive sleep apnoea classified using ODI3% were identified by
AHIflow50%. The overall concordance between AHIflow50% and ODI3% 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,
ODI3% and AHIflow50% from type‐4 sleep studies are at least moderately
discordant. Until further evidence is available, the use of ODI3% as the measure of
choice for type‐4 sleep studies is recommended cautiously.
