INCREASING URINARY COTININE CONCENTRATIONS AT ELEVATED-TEMPERATURES -THE ROLE OF CONJUGATED METABOLITES

The presence of cotinine, a nicotine metabolite, in urine above a spec ified cutoff concentration is commonly used to distinguish smokers fro m nonsmokers, as in smoking cessation studies. A stability study of co tinine in urine was carried out after questions arose concerning analy te stability at elevated storage and shipment temperatures. Aliquots f rom a smokers urine pool were stored at 5, 25, 40, 50 and 60 degrees C for 30 days. Another set of aliquots, obtained by diluting the smoker s pool 1:1 with nonsmokers urine, were stored under the same condition s. Free cotinine levels, determined by a stability-indicating gas chro matographic/mass spectrometric (GC/MS) assay, increased over the 30-da y period at higher storage temperatures. Cotinine concentrations in th e aliquots stored at 60 degrees C, for example, nearly doubled over 30 days (1301 to 2476 ng/ml), with similar proportional increases observ ed in the aliquots diluted with nonsmokers urine. Since cotinine can b e excreted to a large degree as cotinine-N-glucuronide, this conjugate d metabolite was determined by an indirect method. As the storage temp erature increased, the free/conjugated cotinine ratio dramatically inc reased, pointing to cotinine-N-glucuronide as the source of the additi onal free cotinine at the higher storage temperatures. The results of this study are of much practical importance, since urine samples with free cotinine concentrations just below a cutoff value may become posi tive for smoking status if suitably low temperatures cannot be maintai ned during sample handling and shipment. (C) 1997 Elsevier Science B.V .