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Original Research: Sleep Disorders |

Serum Bicarbonate Level Improves Specificity of STOP-Bang Screening for Obstructive Sleep ApneaHCO3 Improves Specificity of STOP-Bang Screen

Frances Chung, MBBS; Edmond Chau, MD; Yiliang Yang, MD; Pu Liao, MD; Richard Hall, MD, FCCP; Babak Mokhlesi, MD
Author and Funding Information

From the Department of Anesthesiology (Drs Chung, Chau, Yang, and Liao), Toronto Western Hospital, University Health Network, University of Toronto, Toronto, ON, Canada; the Department of Anesthesiology (Dr Hall), Dalhousie University and QEII Health Sciences Centre, Halifax, NS, Canada; and Sleep Disorders Center and the Section of Pulmonary and Critical Care Medicine (Dr Mokhlesi), University of Chicago Pritzker School of Medicine, Chicago, IL.

Correspondence to: Frances Chung, MBBS, Room 405, 2McL, Department of Anesthesia, Toronto Western Hospital, 399 Bathurst St, Toronto, ON, M5T 2S8, Canada; e-mail: frances.chung@uhn.ca


Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.

Funding/Support: This work was supported by Physicians’ Services Incorporated Foundation, University Health Network Foundation, ResMed Foundation, and the Department of Anesthesiology and Pain Medicine, University Health Network and Mount Sinai Hospital, Toronto, ON, Canada.


Chest. 2013;143(5):1284-1293. doi:10.1378/chest.12-1132
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Background:  The STOP-Bang questionnaire is a validated screening tool for the identification of surgical patients with obstructive sleep apnea (OSA). A STOP-Bang score ≥ 3 is highly sensitive but only moderately specific. Apnea/hypopnea during sleep can lead to intermittent hypercapnia and may result in serum bicarbonate (HCO3) retention. The addition of serum HCO3 level to the STOP-Bang questionnaire may improve its specificity.

Methods:  Four thousand seventy-seven preoperative patients were approached for consent and screened by the STOP-Bang questionnaire. Polysomnography was performed and preoperative HCO3 level was collected in 384 patients. Study participants were randomly assigned to a derivation or validation cohort. Predictive parameters (sensitivity, specificity, positive and negative predictive values) for STOP-Bang score and serum HCO3 level were calculated.

Results:  In the derivation cohort, with a STOP-Bang score ≥ 3, the specificity for all OSA, moderate/severe OSA, and severe OSA was 37.0%, 30.4%, and 27.7%, respectively. HCO3 level of 28 mmol/L was selected as a cutoff for analysis. With the addition of HCO3 level ≥ 28 mmol/L to the STOP-Bang score ≥ 3, the specificity for all OSA, moderate/severe OSA, and severe OSA improved to 85.2%, 81.7%, and 79.7%, respectively. Similar improvement was observed in the validation cohort.

Conclusion:  Serum HCO3 level increases the specificity of STOP-Bang screening in predicting moderate/severe OSA. We propose a two-step screening process. The first step uses a STOP-Bang score to screen patients, and the second step uses serum HCO3 level in those with a STOP-Bang score ≥ 3 for increased specificity.

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