Dipstick tests for secondhand smoke exposure

We tested TobacAlert and NicAlert immunochromatographic strips for use as indicators of secondhand smoke (SHS) exposure.

Urine samples collected from SHS-unexposed volunteers were spiked with cotinine to concentrations of 5, 8, 13, and 23 ng cotinine/ml urine. One sample was not spiked and used as a control. According to manufacturer's instructions, 45 NicAlert and 45 TobacAlert dipsticks were prepared. The exercise was repeated once. Cotinine levels in urine samples were measured using liquid chromatography/mass spectrometry (LC/MS). STATA was used for statistical analyses.

Ninety NicAlert and 90 TobacAlert dipsticks were tested. Each strip was read by 3 different readers, for 270 NicAlert and 270 TobacAlert readings; 98/270 (36%) NicAlert and 104/270 (39%) TobacAlert readings agreed with the readings predicted by LC/MS-determined cotinine levels. Spearman's rho for the NicAlert strips was .13 and for the TobacAlert strips .23. Both were statistically significant. Using a dichotomous scheme to interpret any strip reading >or=1 as "positive," indicating SHS exposure, NicAlert strips were 94% sensitive and 31% specific, while TobacAlert strips were 89% sensitive and 60% specific.

NicAlert and TobacAlert strips performed poorly at low cotinine levels. While the strips could be used to prescreen samples prior to more accurate testing, their use in the clinical or research setting to indicate SHS exposure should be restricted to carefully selected scenarios.