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Use of on-site testing for illicit drugs in forensic settings

Published online by Cambridge University Press:  02 January 2018

Ian J. Yanson*
Affiliation:
Nottinghamshire Healthcare NHS Trust, Rampton Hospital, Retford, Nottingham DN22 0PD, email: ian.yanson@nottshc.nhs.uk
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Abstract

Type
The columns
Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © Royal College of Psychiatrists, 2009

The paper by Ghali Reference Ghali1 highlights the importance of training staff on the use of on-site urine testing kits. Although they are widely used in forensic settings where testing for illicit drugs forms an integral part of the overall management of patients, Reference Durant, Lelliott and Coyle2 staff receive very little training on the interpretation of test results. There are four possible interpretations: true positive, false positive, true negative and false negative. Reference Wolff, Farrell, Marsden, Monteiro, Ali and Welch3 A true positive test indicates that the person has used the drug, while a true negative test indicates absence of drugs in the sample. On the other hand, a false positive result can occur from the incorrect identification of the presence of substances, failure to acknowledge the chemical similarity of a prescribed medication with the drug of interest, and passive drug exposure. A false negative result may occur when the test's cut-off level is set above the limit of detection of the drug or due to sample adulteration.

A rigid interpretation of test results may have several undesirable consequences. Reference Gordon and Haider4 For instance, a false positive result may lead to false accusations being made against an innocent person resulting in suspension of leave, loss of privileges and possibly discharge from hospital. The last is more likely to be the case in patients with a personality disorder. In contrast, a false negative result may lead to a false perception that things are under control.

Training should incorporate understanding of the context of drug screening and ensuring the quality of samples to minimise errors in test result interpretation.

References

1 Ghali, S. On-site testing for drugs of misuse in the acute psychiatric ward. Psychiatr Bull 2009; 33: 343–6.Google Scholar
2 Durant, M, Lelliott, P, Coyle, N. Availability of treatment for substance misuse in medium secure psychiatric care in England: a national survey. J Forens Psychiatry Psychol 2006; 17: 611–25.Google Scholar
3 Wolff, K, Farrell, M, Marsden, J, Monteiro, G, Ali, R, Welch, S, et al. A review of biological indicators of illicit drug use, practical considerations and clinical usefulness. Addiction 1999; 94: 1279–98.Google Scholar
4 Gordon, H, Haider, D. The use of ‘drug dogs’ in psychiatry. Psychiatr Bull 2004; 28: 196–8.Google Scholar
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