Comparison of serum and salivary cotinine measurements by a sensitive high-performance liquid chromatography-tandem mass spectrometry method as an indicator of exposure to tobacco smoke among smokers and nonsmokers

Exposure to tobacco smoke, both from active smoking and from passive exposure to environmental tobacco smoke, can be monitored by measuring cotinine, a metabolite of nicotine, in a variety of biological sources including blood, urine, and saliva. Previously, a sensitive atmospheric- pressure ionization, tandem mass spectrometric (LC-API-MS-MS) method for cotinine measurements in serum was developed in support of a large, recurrent national epidemiologic investigation. The current study examined the application of this LC-API-MS-MS method to both serum and saliva cotinine measurements in a group of 200 healthy adults, including both smokers and nonsmokers. The primary objective of this study was to evaluate the relationship between serum and saliva cotinine concentrations to facilitate the linking of results from epidemiologic studies using salivary cotinine measurements existing national data based on serum cotinine analyses. The results indicate that a simple, linear relationship can be developed to describe serum and saliva cotinine concentrations in an individual, and the expression describing this relationship can be used to estimate with reasonable accuracy (approximately ± 10%) the serum cotinine concentration in an individual given his or her salivary cotinine result. It was further confirmed that saliva cotinine samples are generally quite stable during storage after collection, even at ambient temperatures, and this sample matrix appears to be well-suited to the requirements of many epidemiologic investigations.