Expired Air Carbon Monoxide Testing Is Effective for Preoperative Screening of Cigarette Use in Orthopaedic Patients: A Prospective Pilot Study of 70 Veterans

Abstract

Introduction: Screening for cigarette use is standard in the orthopedic pre-operative clinic, however traditional biochemical testing methods, including serum and urine cotinine assays, do not differentiate active smoking from nicotine replacement therapy (NRT). In this prospective pilot study, we hypothesize that exhaled carbon monoxide (eCO) testing will be non-inferior to the gold standard serum cotinine (SC) test in screening for pre-operative cigarette use, will differentiate active smoking from NRT, and will allow for substantial cost savings in a clinic setting. Methods: Adult orthopaedic veterans indicated for elective surgery at our institution were offered inclusion. Self-reported smoking status (SRS), eCO and SC levels were obtained preoperatively. An eCO level of >6 parts per million and a SC level >3 ng/ml were considered positive for recent cigarette use. Agreement between SRS, eCO levels and SC levels, and eCO level test-retest reliability were evaluated. Results: Of the 55 patients enrolled into the study, 4 were self-reported Current Smokers and 51 were self-reported Ex-Smokers or Non-Smokers. Combining SRS with eCO levels as a screening tool for recent cigarette use yielded a sensitivity of 100%, a specificity of 98%, a positive predictive value of 95% and a negative predictive value of 100%. eCO testing differentiated NRT from cigarette use in all non-smoking patients. Test-retest reliability for eCO levels showed perfect agreement for 16 patients that had two or more eCO levels pre-operatively. Conclusion: Exhaled CO testing is as effective as SC testing but can differentiate active smoking from NRT, while maintaining a high level of accuracy and reliability when combined with SRS as a screening tool.