The prevalence of alcohol and drugs in sampled oral fluid is related to sample volume.

About 22,000 samples of oral fluid have been collected in five population studies in Norway using either the Intercept or Statsure oral fluid sampling devices. The prevalence of alcohol and drugs was found to be higher in oral fluid samples with small volumes than in those with large volumes for both sampling devices; the largest differences were observed for tetrahydrocannabinol, alcohol, amphetamines, and cocaine/benzoylecgonine when using the Statsure device. Our recommendation is that samples of oral fluid with smaller volume than required by the analytical methods should not be discarded, but instead be analyzed using a smaller sample volume, if necessary, after dilution. If not analyzed, positive drug cases will be missed, and the total prevalence of alcohol and drugs in the population being studied will be underestimated.