What is a D and L isomer test?

If the donor were to claim that they had a methamphetamine positive because they used a Vicks inhaler, then the MRO would order a d/l isomer separation to determine if the drug present in the specimen is at least 80% l-methamphetamine.  If the specimen contains more than 20% d-methamphetamine, then the donor is to be considered positive for illicit methamphetamine use.

The l-form of methamphetamine, which produces primarily peripheral effects, is available OTC in the Vicks and other generic nasal inhalers. D-Methamphetamine abuse is widespread. Methamphetamine labs appear nationwide in primarily rural settings. Street names for the hydrochloride salt include Speed and Crank. The drug may be administered orally in capsules or tablets, snorted, or smoked. 

Methamphetamine (also called meth, crystal, chalk, and ice, among other terms) is an extremely addictive stimulant drug that is chemically similar to amphetamine. It takes the form of a white, odorless, bitter-tasting crystalline powder.