Using expired air carbon monoxide to determine smoking status during pregnancy: Preliminary identification of an appropriately sensitive and specific cut-point |
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Authors: | Beth A. Bailey |
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Affiliation: | Department of Family Medicine, East Tennessee State University, P.O. Box 70621, Johnson City, TN 37614, United States |
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Abstract: | BackgroundMeasurement of carbon monoxide in expired air samples (ECO) is a non-invasive, cost-effective biochemical marker for smoking. Cut points of 6 ppm–10 ppm have been established, though appropriate cut-points for pregnant woman have been debated due to metabolic changes. This study assessed whether an ECO cut-point identifying at least 90% of pregnant smokers, and misidentifying fewer than 10% of non-smokers, could be established.MethodsPregnant women (N = 167) completed a validated self-report smoking assessment, a urine drug screen for cotinine (UDS), and provided an expired air sample twice during pregnancy.ResultsHalf of women reported non-smoking status early (51%) and late (53%) in pregnancy, confirmed by UDS. Using a traditional 8 ppm + cut-point for the early pregnancy reading, only 1% of non-smokers were incorrectly identified as smokers, but only 56% of all smokers, and 67% who smoked 5 + cigarettes in the previous 24 h, were identified. However, at 4 ppm +, only 8% of non-smokers were misclassified as smokers, and 90% of all smokers and 96% who smoked 5 + cigarettes in the previous 24 h were identified. False positives were explained by heavy second hand smoke exposure and marijuana use. Results were similar for late pregnancy ECO, with ROC analysis revealing an area under the curve of .95 for early pregnancy, and .94 for late pregnancy readings.ConclusionsA lower 4 ppm ECO cut-point may be necessary to identify pregnant smokers using expired air samples, and this cut-point appears valid throughout pregnancy. Work is ongoing to validate findings in larger samples, but it appears if an appropriate cut-point is used, ECO is a valid method for determining smoking status in pregnancy. |
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Keywords: | CO, carbon monoxide COHb, carboxyhaemoglobin ECO, expired carbon monoxide ETS, environmental tobacco exposure NPV, negative predictive value ppm, parts per million PPV, positive predictive value ROC, receiver operating characteristic UDS, urine drug screen |
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