Table 1

Biomarkers of secondhand smoke exposure (SHSe), characteristics and cut-off points for distinguishing smokers from non-smokers

BiomarkerHalf-lifeInvasivenessCut-off pointProsCons
Cotinine Reflects recent SHSe
 Urine16 h (average)Non-invasive50 ng/ml for higher SHSeHigher concentrations than other matrices (higher sensitivity)Need of facilities with privacy during collection
Difficulty for population-based or children studies
Need for creatinine clearance adjustment
Collect data on renal disease and some prescription drugs
 Blood16 h (average)Invasive
  • 12 ng/ml for higher SHSe

  • 3 ng/ml for lower SHSe

No adjustment required for hydrationPregnant women have increased clearance rate
Difficulty for infants and young children
Lower sensitivity
 Saliva16 h (average)Non-invasive14 ng/ml for higher SHSeGood for multiple measurements over a limited period of timePotential issues with age, gender, race, oral pH, type of diet, dehydration, or drug treatment
Lower sensitivity
 Hair1 cm of hair proximal to the scalp is approximately equal to the last month's exposureNon-invasive
  • 0.8 ng/mg (women)

  • 0.2 ng/mg (pregnant)

  • 0.2 ng/mg (children)

Easy to collect, ship and store (room temperature ≤5 years)
Less affected by daily variability (fluctuating exposure, varying metabolism and nicotine elimination)
Represents longer exposure
Scarcity of hair in infants and adults
Chemical hair treatments can reduce concentrations by 9% to 30%
Age, gender and race may play roles in determining hair nicotine concentrations
 Toenails1 mm is approximately equal to last month's exposureNon-invasiveNot availableEasy to collect, ship and store (room temperature ≤20 years)
Overcomes day-to-day exposure variability
Represents longer exposure
Need for further research and population concentrations
 UrineUp to 3 weeksNon-invasiveNot availableRelated to a lung carcinogen
Represents longer exposure than cotinine (urine/blood/saliva)
Analytical expertise
Costly equipment
NNAL is carcinogenic and mutagenic, special lab handling
Further research needed
  • * NNAL (4-[methylnitrosamino]-1-[3-pyridyl]-1-butanol).