In recent years, there has been a growing debate surrounding the need for D and L isomer testing as a follow-up to positive methamphetamine results in liquid chromatography-mass spectrometry (LCMS) urine drug testing. The reflex to D and L testing following positive methamphetamine results has been considered standard practice. However, scientific evidence and an evaluation of the benefits of D/L testing do not outweigh the drawbacks.

Methamphetamine is metabolized in the body primarily into its D-isomer, d-methamphetamine, which is the active component responsible for the drug's psychoactive effects. The L-isomer, l-methamphetamine, is a less potent and biologically inactive form which may also be present in illicit methamphetamine. Thus the presence of any d-methamphetamine in urine serves as a reliable indicator of methamphetamine use.

LCMS urine drug testing is a highly sensitive and selective method for detecting methamphetamine and its metabolites. Studies have shown that LCMS reliably identifies d-methamphetamine (the isomer most commonly detected on routine LCMS drug testing panels) which is sufficient evidence of recent methamphetamine use. Given the sensitivity of this testing method, the need for additional D and L isomer testing may be unnecessary to determine illicit drug use. Differentiating between D and L isomers requires specialized analytical methods, such as chiral chromatography, which are not routinely employed in standard LCMS urine drug testing protocols since it requires unique sample preparation and testing technology. Incorporating D and L isomer testing adds complexity to laboratory procedures, requiring additional time, resources, and expertise. Moreover, these specialized tests come at a higher cost and are typically not covered by insurance benefits thereby placing an unnecessary burden on patients.

From a clinical standpoint, distinguishing between d-methamphetamine and l-methamphetamine does not provide meaningful information for patient management. The presence of d-methamphetamine indicates recent methamphetamine use, which is the critical factor in assessing compliance or addressing substance abuse issues. The identification of l-methamphetamine does not contribute to the clinical interpretation nor rule out the use of methamphetamine.

Professional guidelines and consensus statements support the limited clinical value of D and L isomer testing following positive methamphetamine results. The Substance Abuse and Mental Health Services Administration (SAMHSA) guidelines do not require D and L isomer testing as a routine follow-up for methamphetamine detection in workplace drug testing programs. These guidelines emphasize the importance of accurate detection of d-methamphetamine without necessitating the additional isomer testing.

Based on the scientific evidence presented, it is suggested that providers utilizing drug testing for patient care reassess the need for D and L isomer testing and consider evidence-based approaches that prioritize accurate detection of d-methamphetamine while minimizing unnecessary financial burden on patient. By aligning with current scientific consensus, we can ensure that drug testing practices are efficient, cost-effective, and rooted in the best interests of patients and the wider healthcare community.

Vipin Adhlakha - CEO Aria Diagnostics