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Introduction Rapid assessment of overnight desaturation is key in diagnosing Obstructive Sleep Apnoea (OSA). OSA can be diagnosed with home sleep studies; using overnight oximetry with access to multichannel services if results are normal but patients are symptomatic. 1 We sought to determine whether there were any predictive factors differentiating patients who required CPAP following completion of both overnight oximetry and multi-channel studies compared to those that were discharged.Method 73 patients completed two nights of Oximetry followed by a two night Multichannel sleep study. Patients completed questionnaires to score Epworth Sleepiness Scale (ESS), measurements of age, height, weight, neck circumference and Body Mass Index (BMI) prior to initial oximetry.Results 30 patients required CPAP therapy and 43 were discharged. There was no significant difference in ESS, neck circumference, age and BMI between groups. The overnight oximetry results, measured using ODI and SpO 2 were similar within the groups. The range of the AHI measured using Multichannel devices was similar between groups. We did find a higher average AHI in the CPAP group, this group were predominantly male, 64% in the CPAP group compared to 37% in discharged group.Abstract P59 Table 1Values from Overnight Oximetry (Oxim) and Multichannel (MC). Apnoea-Hypopnea Index (AHI) and Oxygen Desaturation Index (ODI)Conclusions On reviewing both Oximetry and multichannel data, a higher average Oxim ODI and MC AHI in the CPAP group was noted in comparison to the discharged patients that were discharged with majority of patients falling into the moderate OSA category requiring CPAP. There was minimal difference in questionnaires and demographics identified between the two groups other than gender difference. Studies have shown that due to differences in sleep latency, upper airway fat distribution and difference in hormonal profile, men have a higher risk of developing OSA. 2 Screening Oximetry remains a useful tool to identify OSA, however Multichannel studies allow more sensitive diagnosis in patients with normal oximetry if clinical suspicion of OSA is high.References Nice Guidelines; 2021. ( Obstructive sleep apnoea/hypopnoea syndrome and obesity hypoventilation syndrome in over 16s)Lin CM, Davidson TM, Ancoli-Israel S. (2008). Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC2642982/#R27