ORALVEQ: external quality assessment scheme of drugs of abuse in oral fluid: results obtained in the first round performed in 2007.

The Institut Municipal d'Investigació Mèdica IMIM-Hospital del Mar (Barcelona, Spain) in cooperation with the Istituto Superiore di Sanità (Rome, Italy) organized an external quality assessment scheme to assess the reliability of analytical laboratories when analyzing drugs of abuse in oral fluid (ORALVEQ). For the first round of ORALVEQ, performed in February 2007, three different samples (S1, S2 and S3) were sent to 21 participating international laboratories. S1 was a blank sample and S2 and S3 were prepared by addition of drugs at known concentrations to pre-screened drug-free oral fluid (containing sodium azide) and diluted up to 50% with acidic buffer. S2 contained 6-monoacetyl morphine, morphine, cocaine and benzoylecgonine and S3 contained 3,4-methylendioxymethamphetamine and 3,4-methylendioxyamphetamine. Results were evaluated from a qualitative and quantitative point of view. Whereas only half laboratories performed screening analysis, all of them reported a quantitative result for almost all analytes. Eighteen false-positive and 3 false-negative results were reported by 8 (from a total of 21) laboratories. The quantitative evaluation was performed measuring dispersion (% coefficient of variation, CV%) and accuracy (% error, ERR%) of results and calculating the z-score values (using robust statistics). ERR% between 2% and 20% and CVs% around 40% were obtained for all analytes. In terms of z-score, a high percentage of adequate results (between 85 and 95%) was obtained. In general, the participating laboratories had a satisfactory performance. The number of false-negatives reported was very low, the false-positives were reported by a reduced number of laboratories and the scatter in the quantitative results was principally due to a few outlying values; since applying robust statistics, there was no rejection of outliers.