Objective: To evaluate the effect of arterial blood HCO3- level on the accuracy 
of NoSAS questionnaire screening for obstructive sleep apnea hypopnea syndrome 
(OSAHS). Methods: The hospitalized patients with suspected OSAHS were recruited 
from March 2016 to December 2017 in the First Affiliated Hospital of Guangzhou 
Medical University. NoSAS scores, blood gas analysis and polysomnography (PSG) 
were performed in these patients. Patients were divided into non OSAHS group and 
mild, moderate and severe OSAHS group according to the PSG results. According to 
the NoSAS questionnaire score, the patients were divided into OSAHS high-risk 
group and low risk group. The correlation between arterial blood HCO3- level and 
apnea hypopnea index (AHI) was analyzed. The receiver operating characteristic 
(ROC) curve was plotted to analyze the accuracy of HCO3- prediction OSAHS. 
Predictive parameters(sensitivity, specificity, positive and negative predictive 
values)for NoSAS scores and HCO3- level were calculated. Results: A total of 243 
patients with suspected OSAHS were included, including 186 males (76.5%), 57 
females (23.5%), age (49±13) years, body mass index (BMI) (26.9±4.4) kg/m2, and 
neck circumference (38.6±4.5) cm. The HCO3- level was positively correlated with 
AHI (r=0.206, P=0.001). The proportion of patients with HCO3- level ≥26 mmol/L 
in non-OSAHS group was lower than that in OSAHS group (13.0% vs 34.5%, P=0.004); 
the proportion of patients with HCO3- level ≥26 mmol/L in severe OSAHS group was 
higher than that in mild OSAHS group (37.7% vs 15.0%, P=0.008), and there was no 
difference in the ratio of patients with severe OSAHS and moderate OSAHS (37.7% 
vs 35.3%, P=0.767). The specificity of OSAHS predicted by HCO3- level 25 and 26 
mmol/L was 69.6% and 87.0%, respectively. With the NoSAS score of 8 or 7 as 
cutoffs for analysis, the sensitivity for OSAHS was 61.9% and 79.2%, the 
specificity for OSAHS was 57.4% and 40.4%, respectively. With the addition of 
HCO3- level ≥ 26 mmol/L to the NoSAS score ≥ 7, the specificity for OSAHS 
improved to 93.6%, while the sensitivity decreased to 27.4%. Conclusion: 
Combined with the arterial blood HCO3- level, the specificity of the NoSAS 
questionnaire increases and the sensitivity decreases.