Total bed time underestimates OSA severity

Using total bed time instead of total sleep time underestimates the severity of obstructive sleep apnoea (OSA), particularly among older patients, according to a recent Singapore study.

“Our study showed that use of total bedtime rather than sleep time led to significant misclassification of OSA, with both underdiagnosis and underestimation of severity,” the researchers said. “Age and body mass index (BMI) were identified as positive and negative predictors of misclassification, respectively.”

The researchers conducted a retrospective observational study, including 1,621 patients who had undergone sleep studies in the National University Hospital, Singapore. The primary outcome was misclassification of OSA, defined as an underestimation of its severity when using total bed time (measured through the respiratory-event index) rather than total sleep time (measured through the apnoea-hypopnoea index).

Before the sleep studies, 98.2 percent of the participants were diagnosed with OSA. According to the total sleep time tests, however, only 93.6 percent (n=1,518) of patients have OSA. In contrast, total bed time yielded an even lower estimate, suggesting that only 91.2 percent (n=1,479) had OSA. [Sci Rep 2021;11:11481]

Overall, using total bed time led to 300 OSA misclassifications relative to total sleep time, corresponding to 18.5 percent of the study population (p<0.005). Even when stratifying according to OSA severity, total bed time still led to significant misclassifications.

The researchers then performed logistic regression analysis to identify potential predictors of OSA misclassification. After multivariate adjustment, age emerged as a significant and positive predictor of misclassification (odds ratio [OR], 1.02, 95 percent confidence interval [CI], 1.01–1.03; p=0.001), while BMI had an inverse effect (OR, 0.97, 95 percent CI, 0.95–0.99; p=0.015).

Subgroup analysis further refined these associations and revealed that OSA misclassification was driven most strongly by those aged ≥57 years (vs <33 years; OR, 2.25, 95 percent CI, 1.58–3.21). In contrast, participants with BMI ≥32.3 kg/m² (vs <25 kg/m²; OR, 0.69, 95 percent CI, 0.48–0.98) saw significantly lower odds of being misclassified.

“The clinical implications of our study would be that the use of home sleep apnoea testing needs to be done with caution, especially in a patient population at high pretest risk of moderate OSA, as misclassification may result in the appropriate therapies not being offered,” the researchers said, noting  how patients might be lulled into thinking that their OSA is less severe than it actually is, and hence less motivated to adhere to therapy.

“Future research in this field could delve into affirming the results of this study with a randomized control trial of older patients with lower BMI undergoing either home sleep test or polysomnography,” they said. “Other aspects to consider will include looking into how processes can be changed in the sleep clinic to flag up patients who may not be suitable for home sleep apnoea testing.”