SPECIALIST PHARMACOLOGICAL & BIOCHEMICAL INTERVENTIONS
BODY MATRIX
The body matrix used has implications for test results in several ways:
- Recency of drug use: typically urine will indicate drug use within the last 48 hours or so, whilst plasma indicates use within the last period of hours and hair within the last period of months.
- Accuracy of results: very large amounts of drug are excreted into the urine allowing for easier detection by the laboratory technology than with saliva or hair.
- Quantitation of results: if a quantitative level of drug is to be measured, the only suitable matrices are plasma or saliva.
Whilst saliva (or oral fluid or oral mucosal transudate) offers many potential advantages over urine as a testing matrix, the current technology has not yet developed to the extent that saliva should routinely be used in preference to urine. In the laboratory a greater number of extraction steps are required relative to urine which increases cost. The concentrations of drugs are lower and the window of detection shorter than for urine, both of which increase the number of false negative results obtained. Currently few immunoassays exist which can detect the unique profiles of drugs in saliva, meaning that more expensive technology often has to be used for screening. Nevertheless, the many potential advantages of saliva over urine as a matrix means that this is a rapidly developing area of reseach, and in due course saliva (or oral fluid or oral mucosal transudate) will probably become the matrix of choice for drugs of misuse testing.
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The above information is copyright of Dr Bruce Trathen MBBS MRCPsych (2006). ISBN 0-9545164-0-0. The author grants permission for these guidelines to be downloaded, copied and distributed freely, but does not grant permission for their sale.
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