Study Objective: To determine the value of home oximetry as a screening test in patients with moderate to severe symptoms of obstructive sleep apnea (OSA).
Design: Retrospective, observational study.
Setting: The Sleep Unit of a tertiary referral, university hospital.
Patients: 116 patients referred for evaluation of moderate to severe symptoms of OSA in which both home oximetry and polysomnography (PSG) were performed.
Interventions: N/A
Results: Three numerical oximetry indices were evaluated: average of desaturations ≥4% and average of resaturations ≥3% per hour of analysis time (DI4% and RI3%, respectively); and cumulative percentages of time spent at saturations below 90% (CT90%). A qualitative assessment was also performed. Oximetry indices were compared with apnea/hypopnea index (AHI) by simple linear regression and Bland-Altman analyses. Optimal cut-off points, in terms of sensitivity and specificity, for the oximetry indices were searched using ROC analysis, at an AHI threshold of ≥10. The correlation between AHI and the desaturation indices was r = 0.50 for CT90%, r = 0.60 for DI4%, and r = 0.58 for RI3%. No bias was found between PSG and oximetry indices in Bland-Altman plots. Neither the numerical indices nor the qualitative analysis achieved an adequate (>0.8) area under the ROC curve. A CT90% <0.79 excluded OSA with 84% sensitivity. A DI4% ≥31.4 or a RI3% ≥40.5 diagnosed OSA with 97% specificity. Using these values, 38% of the patients would have been correctly classified by oximetry alone, 10% would have been incorrectly classified, and 50% could not have been classified with certainty. Eleven (15%) OSA patients would have been missed by oximetry.
Conclusions: Correlation between home oximetry and PSG was not high. Oximetry was more useful to confirm than to exclude OSA in our study. Qualitative assessment was not better than numerical analysis. The greatest value of oximetry in this setting seems to be as a tool to rapidly recognize and treat more severe OSA patients in waiting list for PSG.
Abbreviations: OSA= obstructive sleep apnea
PSG= polysomnography
DI4%= desaturations index of ≥ 4%
RI3%= resaturations index of ≥ 3%
CT90%= cumulative percentages of time at saturations below 90%
AHI= apnea/hypopnea index
COPD= chronic obstructive pulmonary disease
ROC= receiver operating characteristic