"The Act of July 31th 2009 which introduces the oral fluid drug testing in traffic, became operational the first of October 2010. This test replaces the former procedure of urinalysis, which was considered to be too complex and too time-consuming for the police authorities (see also Chapter 9). Besides these objections, questions were raised whether the urinalysis and the ensuing blood sample analysis were reliable. The former detected the presence of THC even when the subject was no longer in a state of modified consciousness. The blood analysis also revealed that 20% of the positive urine tests were ‘false positives’, consequently resulting in an unjustified suspension of the drivers licence.
"The implementation of the procedure on oral fluid analysis was accompanied by two Royal Decrees. The first Royal Decree regulates the checklist that precedes the oral fluid test to assess the indications of recent drug use; the second Decree regulates the ensuing blood analysis to determine the amount of drugs used.
"On September 29th 2010, the Minister of Justice and the Council of Prosecutors-general issued a circular to harmonize the investigation and prosecution policy on driving under the influence of drugs. It replaces the previous circulars on this matter and comes into force on October 1st 2010, at the same time as the oral fluid drug testing. The circular also elucidates the former mentioned Royal Decrees."

Source

Deprez, Nathalie, et al., "2011 National Report (2010 data) to the EMCDDA by the Reitox National Focal Point" (Brussels, Belgium: OD Public Health and Surveillance, Scientific Institute of Public Health, October 2011), WIV-ISP/EPI REPORTS N° 002, pp. 23-24.
http://www.emcdda.europa.eu/a…