Determination of a saliva cotinine cut-off to distinguish pregnant smokers from pregnant non-smokers.
BACKGROUND
Objective validation of smoking status is necessary. Earlier studies have used saliva cotinine concentrations between 14.2 and 30 ng/ml as cut-off values to distinguish pregnant smokers from non-smokers. However, these cut-offs derive from studies including men and non-pregnant women. This constitutes a problem, as recent studies have reported an accelerated metabolism in pregnant smokers. The aim of this study was to determine the optimum cut-off cotinine level distinguishing pregnant smokers from pregnant non-smokers.


METHODS
An observational study of 620 pregnant women, 359 self-reported smokers and 261 self-reported non-smokers, with complete data on smoking status and saliva cotinine. The study was conducted at a large university hospital in Copenhagen, Denmark. Saliva was sampled at the first antenatal visit to the midwife and analyzed for cotinine level by gas chromatography. Participants completed a questionnaire immediately after the first visit.


RESULTS
A saliva cotinine cut-off level of 13 ng/ml, corresponding to a sensitivity of 0.99 and specificity 0.98, was found to be the optimum cut-off value separating pregnant smokers from non-smokers. The sum of the sensitivity and specificity was at its maximum, 1.981. A 95% bootstrap confidence interval for the optimum cut-off was (8-14 ng/ml).


CONCLUSIONS
From the present data we recommend that in future studies on smoking cessation and pregnancy a cut-off level of 13 ng/ml should be applied to distinguish between pregnant smokers and non-smokers.
Hegaard
Hanne K
HK
Department of Obstetrics and Gynaecology, Hvidovre Hospital, Denmark. Hanne.Hegaard@rh.dk
Kjaergaard
Hanne
H
Møller
Lars F
LF
Wachmann
Henrik
H
Ottesen
Bent
B
D000328:Adult; D016022:Case-Control Studies; D002849:Chromatography, Gas / Q000379:methods; D003367:Cotinine / Q000032:analysis*; D005260:Female; D006801:Humans; D007202:Indicators and Reagents / Q000032:analysis; D011247:Pregnancy / Q000378:metabolism*; D011248:Pregnancy Complications / Q000517:prevention & control; D011295:Prenatal Care; D011322:Primary Prevention; D012372:ROC Curve; D012015:Reference Standards; D012016:Reference Values; D015203:Reproducibility of Results; D012463:Saliva / Q000737:chemistry*; D012650:Self Disclosure; D012680:Sensitivity and Specificity; D012907:Smoking / Q000453:epidemiology / Q000378:metabolism*; D011795:Surveys and Questionnaires
D007202:Indicators and Reagents; D003367:Cotinine