Background The accurate determination of smoking habit is important for the treatment of smoking-related disease. Cotinine, the major metabolite of nicotine is the analyte of choice to assess smoking habit. A number of point-of-care urine cotinine tests are used to validate self-reported smoking and in some instances, provide feedback to improve smoking cessation. Urine testing is inappropriate in some instances, and while saliva testing is more acceptable, it is more difficult because cotinine is in lower concentrations compared to urine. A prototype saliva test was developed and evaluated, but the colorimetric assay was deemed inadequate. A new, more sensitive assay has been developed and evaluated in a group of healthy volunteers.
Method Volunteers (n=117), aged between 22 and 67 years (36% female), including 61 smokers with a cigarette consumption of five or more cigarettes/day, (mean 16.0), provided a saliva sample using a manufactured collecting device. One ml of saliva was eluted using the test's fixed-volume syringe. The sample was introduced onto freeze-dried reagents and quickly shaken. A sample positive for nicotine metabolites would be expected to turn pink within 1 min, but 4 min were allowed for full colour development. The resultant colour was compared with a four-point colour chart and the level of smoking recorded. Samples from non-smokers should remain unchanged.
Results A positive colour change wasobtained from 56 of the 61 smokers and a negative result from 54 of the 56 non-smokers, giving a sensitivity of 92% and specificity of 96%. The semi-quantitative results correlated with daily cigarette consumption; with light smokers (5–10 per day, n=15) mean 2.3, 11–15 per day (n=14) mean 2.8, 16–20 per day (n=19) 3.4 and more than 20 per day (n=8) mean 3.0 (p<0.05).
Discussion The new test was found to be superior to the prototype, being quicker and the final colour easier to read. The saliva collection device was also an improvement on previous methods. The sensitivity and specificity were comparable with the other commercial saliva cotinine test available. A dedicated colorimeter to quantify the result is under development. This test could be an important adjunct for treating smoking-related disease.
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