Understanding Lab Results – Part 2

Jan 4, 2018

Part II: Interpreting Results

What happens once the sample has been tested?

While the measurement of compounds found in samples can be a precise science, the interpretation of those results is ultimately decided by clinicians in consult with a laboratory toxicologist. It is important that the technician takes into consideration any medication ingested by the client, as well as the client’s medication history, and does not use a positive test result as a confirmation of substance abuse or addiction. As well, it is vital to differentiate between the metabolites present in the sample, as just because one or more metabolites are present, does not mean those particular drugs were injested. For example, codeine and morphine can be detected in urine after the client uses heroin, and oxymorphone can be detected after the client has used oxycodone.1

What is an abnormal result?

An abnormal result occurs when the test does not display results that align with anecdotal assumptions. For example, if a patient has been prescribed medication, but that compound does not appear in the test, it is considered an abnormal test result and can be explained by several factors, including the patient running out of, or not taking enough of, the prescribed medicine, or that the sample has been tampered with. Another abnormal test would be results that indicate the presence of a substance that has not been prescribed to the patient. In this case, physicians should consider a false positive result, where non-illicit drugs can appear to be illicit due to cross-reactivity, or that the patient has ingested various non-illicit substances, like poppy seeds, which have metabolized into a compound normally produced by an illicit drug.
For all abnormal tests, physicians take into account the possibility of lab error, the concentration/dilution levels of the sample, and the varying metabolic rates of each patient, which can affect how much of the drug appears in each sample.

What happens when the sample tests positive?

When a drug test is positive, technicians are advised to discuss the results with the patient in a non-judgemental way rather than make assumptions about the patient’s drug use habits. If it is discovered that the presence of the drug is the result of an addiction, referral to addiction counselling often occurs, and federal regulations for prescribing substances to a person dependent on drugs should be adhered to.2


1.“Interpreting Test Results.” Interpreting Test Results | OpioidRisk, www.opioidrisk.com/node/490
2. “Interpreting Test Results.” Interpreting Test Results | OpioidRisk, www.opioidrisk.com/node/490