They found that all the laboratories in their study could reliably distinguish between samples from regular smokers and samples from nonsmokers. In addition, all the laboratories provided selleck chemical Trichostatin A consistent ranking of results for serum cotinine. However, there were often substantial differences in the concentrations measured by the participating laboratories in that study. These authors concluded that whereas classification of smoker versus nonsmoker by cotinine analysis was generally reliable, the individual values measured by different laboratories could vary considerably. There were also substantial differences noted in that study between RIA and GC results in urine samples, although not in serum, probably reflecting the influence of possible cross-reaction in the RIA with cotinine glucuronides and 3-hydroxycotinine in the urine measurements.
More recently, a common set of urine samples was evaluated for their cotinine concentrations by a group of six European laboratories using high-performance liquid chromatography-ultraviolet (HPLC-UV) and immunoassay methods; generally, good agreement was noted within the group (Jacob et al., 2005). However, in that study, all participating laboratories were required to use the same standardized procedure for the HPLC-UV assays. As in the study by Biber et al. (1987), some differences were noted between liquid chromatography (LC) and immunoassay methods, presumably again involving the cross-reactivity of other analytes in the urine samples during the immunoassays, especially 3-hydroxycotinine.
Current analyses of cotinine in samples from nonsmokers may place increasingly greater stress on the assays because the concentration levels are often quite low. Nevertheless, maintaining good accuracy and precision in these assays is important for facilitating comparisons among studies. In some cases, even relatively small mean concentration differences between groups of nonsmokers may be of interest. Fortunately, there have been improvements in the available analytical methodology in recent years. Current assays using capillary GC with nitrogen�Cphosphorus detectors (GC/NPD) or, in some cases, mass spectrometric (GC/MS) detection or LC coupled with tandem mass spectrometry (LC/MS/MS) may be expected to provide both for more sensitive and more precise measurements than were available in the past.
To evaluate the current state of serum cotinine measurements in smokers and nonsmokers with a particular emphasis on the latter, we have undertaken a study of the analysis of a common set of GSK-3 serum samples by seven laboratories experienced in these assays. Our objectives in this work were to assess the current state of cotinine analyses using modern analytical techniques and to provide consensus values for a set of serum samples that might then be used in support of further method validation activities in the future.