Objective: To compare two-hour daytime polysomnography (DPSG) and overnight polysomnography (ONPSG) (as the gold standard) in screening for high risk snorers.
Study design: Descriptive study (Diagnostic test).
Setting: Snoring Clinic, Phramongkutklao Hospital.
Material and Method: The present study was carried out among patients attending the Snoring clinic at Phramongkutklao hospital from September 2005 to February 2006 who had high risk of sleep apnea (pre-test) and scheduled for overnight PSG. Additionally, subjects were willing to take a two-hour daytime polysomnography. Both tests were performed less than two months apart. Each case was assessed using the Epworth Sleepiness Scale (ESS) > 8/24 and/or BMI > 27.5 kg/sqm as criferia to define as high risk snorer. After performing polysomnography, the subjects were categorized as high risk obstructive sleep apnea syndrome (OSAS, AHI > 20/hour) and low risk OSAS (AHI < 20/hour). Regarding snoring sound, subjects were divided into three groups: mild, moderate and severe.
Results: Fifty subjects, 33 males and 17 females, were enrolled in the present study. Two males were excluded due to a daytime PSG recording less than two hours. The mean age was 48.3 + 10.64 years (22-65), mean BMI was 27.69 + 3.95 kg/sqm (22.5-36.9) and ESS 10.56 + 2.25/24. The mean AI and AHI for daytime PSG vs. overnight PSG were 24.31 + 21.36, 28.30 + 21.44 vs. 22.39 + 20.43 and 25.30 + 20.91 respectively. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of daytime PSG compared with overnight PSG were 92%, 91.3%, 92% and 91.3% respectively. The agreement of snoring during day and night (K-value) was 0.716 + 0.1 (p = 0.03).
Conclusion: Sleep parameters (AI, AHI) for daytime PSG had high sensitivity, specificity, PPV and NPV compared with standard overnight PSG. These can be used as reliable screening tests for high risk snorers and also be used to assess the outcome of OSAS patients undergoing surgical intervention.

Keywords: Daytime PSG, Snoring intensity, Overnight PSG, Midazolam, Sleep disorder breathing, Obstructive sleep apnea