Analysis of oral fluid samples results by LC-MS/MS and comparison with law enforcement screening: A 6-year study

Aim

Oral fluid samples are gradually replacing blood samples, saving time, space and representing non-invasive collection. The aim of this retrospective study was to determine the substances found in salivary samples analyzed by LC-MS/MS and to compare them with those found in screening tests carried out by law enforcement agencies.

Method

This study focuses on the results of narcotics research on salivary screenings received in our laboratory, over 6 years (2018–2023). The salivary swabs were discharged into Quantisal buffer, placed in ultrasound baths and centrifuged. Internal standards solution was added. The narcotics were then extracted in solid phase. Analyses were performed by LC-MS/MS.

Results

In all, 2888 oral fluid samples were analyzed, with an increase of oral fluid analyses files since 2021 (16.8% increase).

Over time, requests for narcotics testing had become more targeted, focusing solely on the class of narcotics that were tested positive. In 2018, the majority of requests were for all narcotics (59% of the total number of samples), compared with 25% in 2023. In contrast, the specific demand for cannabis has risen from 35% in 2018 to 66% in 2023.

By far the most frequently found substance was THC, detected on average in 92.4% of saliva analyzed per year, either alone or in association with one or more other substances, notably CBD. The number of cases with THC found alone had gradually declined, with a parallel increase in the detection of the THC + CBD combination. CBD detection had increased over the years, since it was found only 55 times in 2021 (14%), whereas it represented 64.9% in 2023. CBD alone was found in only 3 of the 2888 saliva analyzed. These increasing CBD and THC association results may be explained by THC smokers using both THC and CBD, in an attempt to evade the law by claiming that the THC found came from their CBD consumption. Cocaine was found in 10.8% of saliva analyzed, MDMA in 1.3%, codeine in 1.9% and morphine in 0.7%. 6-MAM (0.7%), amphetamine (0.4%), acetylcodeine (0.3%) and heroin (0.3%), pholcodine in only 2 cases, methamphetamine in 5, pseudoephedrine in 3 and MDEA in 1 case were also found. Although not requested, ketamine was detected in 5 cases, always associated with cocaine.

For the majority of cases, the LC-MS/MS results correlated with the screenings, but 8,9% (259 of 2888) were false positives (positive screening and absence of the substance in LC-MS/MS), and of these, 2,2% of results were totally negative, probably reflecting false positives linked to the oral fluid screening device or transcription errors. Among these, the most significant were false positives for amphetamines (81% false positives among 128 amphetamine screenings), followed by opiates (31 among 52, 59%) and cocaine (46 among 219, 21%). Although rarer, there were false positives for cannabis (18 out of 259 false positives: 9.1%), but only 18 out of 1621 (total number of positive cannabis screenings [1.1%]). There were also some false negatives (20 of 2888), the most frequent being results obtained in LC-MS/MS following a positive amphetamine screen and a requisition for all 4 narcotics. These results show how important it is to ask for all narcotics, so as not to miss any susbtances.

Conclusion

This study showed the value of confirming salivary samples by LC-MS/MS, and highlighted the high preponderance of THC and the THC + CBD combination in the results. Quantitative oral fluid samples collection system could distinguish cannabis smokers from CBD users.

Ketamine was also found, so looking further ahead, the search for NPS, particularly in screen-negative samples, would be a very interesting subject for study.