Serum bicarbonate level improves specificity of STOP-Bang screening for obstructive sleep apnea

Chest. 2013 May;143(5):1284-1293. doi: 10.1378/chest.12-1132.


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.

Publication types

  • Evaluation Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Bicarbonates / blood*
  • Biomarkers / blood
  • Cohort Studies
  • Female
  • Humans
  • Male
  • Mass Screening / methods*
  • Middle Aged
  • Polysomnography
  • Predictive Value of Tests
  • Reproducibility of Results
  • Sensitivity and Specificity
  • Severity of Illness Index*
  • Sleep Apnea, Obstructive / blood
  • Sleep Apnea, Obstructive / diagnosis*
  • Surveys and Questionnaires*


  • Bicarbonates
  • Biomarkers