What are the differences among urine, saliva, and serum cotinine levels?
Serum is the specimen of choice for cotinine measurement since it is subject neither to bacterial degradation nor sample concentration. Cotinine can also be measured in saliva in concentrations similar to those in serum; however sample collection is cumbersome as is sample extraction. Most cotinine is excreted by the kidneys into the urine, where it is concentrated about 10X higher than it is circulation. This makes it the specimen of choice for determination of passive exposure. Urine, while easy to collect from children, is subject to contamination and should be kept cold prior to shipping. FBR’s assay can reliably detect cotinine levels consistent with passive (second-hand smoke) exposure in serum and urine.
