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

The paper by Ghali ¹ 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, ² 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. ³ 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. ⁴ 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.