TIAFT Young Scientists "Workshop 2001"

The use of oral fluid and sweat wipes for the detection of drugs of abuse in impaired drivers

Nele Samyn, Bart Viaene, Bart Laeremans, Gert De Boeck

National Institute of Criminalistics and Criminology, Vilvoordsesteenweg 100, 1120 Brussels, Belgium

In march 1999, the Belgian parliament adopted a law on driving under the influence of certain psychoactive drugs. A driver is sanctioned if THC, cocaine, benzoylecgonine, morphine, amphetamine, MDMA, MDEA or MBDB are detected in blood in concentrations exceeding the analytical cut-off values mentioned in the law. An initial suspicion of impairment is established using a limited drug recognition test battery, followed by a urine test on-site.

During the course of this study, newly trained police officers evaluated over two hundred drivers. For over a hundred subjects, oral fluid (obtained by spitting) and sweat samples (obtained with a sweat wipe moistened with 70% of isopropanol) were quantitatively analysed and compared to the corresponding blood and urine results. The reliability of Drugwipe (Securetec, Germany) in an on-site situation is assessed by means of the blood, saliva and sweat confirmatory results obtained with GC-MS.

The prevalence of positive samples was high due to the selection of subjects before sampling. The probability that a positive oral fluid result for a certain drug class will match a positive blood result is expressed as the positive predictive value (PPV). PPV's were excellent (>90%) for amphetamines, cocaine and cannabis. Due to the low prevalence of opiates in our study, the PPV of 78% for opiates needs to be taken with caution. These values are calculated when the limit of detection for both bodyfluids was taken as the cut-off value. When the legal limits for blood were applied, in addition to the proposed SAMHSA cut-off values for oral fluid, the PPV remained high for amphetamines, cocaine and cannabis but decreased for opiates. The probability that a positive sweat wipe result matched a positive blood result was lower than for oral fluid in the cannabis and opiates class, but remained high for cocaine and amphetamines.

The sensitivity of the Drugwipe test on the tongue varies between 45 % for opiates and 77 % for amphetamines, when saliva is taken as the confirmatory matrix. The sensitivity of the Drugwipe sweat test in the detection of opiates, cocaine and amphetamines is respectively 62 %, 67 % and 92 %. The agreement between Drugwipe results and blood analysis is acceptable for amphetamine and/or MDMA, especially when using sweat as the screening matrix.

Undoubtedly, oral fluid and sweat offer a better non-invasive way of screening at the roadside because of the possibility of direct supervision. Saliva analysis is the only alternative to blood sampling to assess impairment related to drug abuse. For roadside testing purposes, a screening test should only require a small amount of sample to facilitate the collection. The Drugwipe test uses a simple procedure. Sweat testing is very easy in a DUID situation but external contamination of the skin needs to be taken into consideration. Any correlation with the presence of a pharmacological effect at the time of sampling is ruled out. However, as an indication of potential drug abuse and in addition to the drug recognition test battery, sweat testing might be preferable to urine testing.

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