Tobacco Use Classification by Inexpensive Urinary Cotinine Immunoassay Test Strips

Urinary cotinine is one of the most commonly measured biomarkers reflecting recent exposure to nicotine. In some cases a simple qualitative dichotomization of smokers and non-smokers is all that is required. NicAlert® test strips have been evaluated for this purpose, but other recently introduced, inexpensive single-line test strips have not. In this study we evaluated two such strips with nominal cutoffs of 200 and 10 ng/mL. A total of 800 urine samples with known cotinine concentrations determined by an LC–MS-MS method were examined, including 400 urine samples ranging from 0.23 to more than 24,000 ng/mL by the 200 ng/mL strip, and 400 samples with concentrations <200 ng/mL by the 10 ng/mL cutoff strip. Both test strips performed well in these evaluations. Classification relative to LC–MS-MS by the 200 ng/mL strips had a sensitivity of 99.5% and specificity of 92%, with 95.8% accuracy. The 10 ng/mL strips had a sensitivity of 98.7% and specificity of 90.1%, with 93.3% accuracy. The positive predictive value for the 200 ng/mL strips was 92.6% and the negative predictive value was 99.5%. For the 10 ng/mL strips, the corresponding values were 85.4 and 99.2%, respectively. The prevalence of positive samples was 50% in the 200 ng/mL group, and 37% in the 10 ng/mL set. Each strip was read by two readers with an overall agreement of >98%. Our results suggest that these simple and inexpensive lateral flow immunoassay test strips can provide useful qualitative estimates of nicotine exposures for appropriate applications within the inherent limitations of sensitivity and precision of the immunoassay test strip format.