In recent years, drug testing has been increasingly implemented as a harm reduction strategy across many Canadian provinces in order to identify components of illicit drugs with the aim of preventing drug-related overdose.

In this second part of our review, we will examine some of the least discriminatory current methods used to test illicit drugs.

Microcrystalline tests

How they work This technique involves the formation of microcrystals in the sample when a specific chemical is added. Then, the crystal formation is compared to a known standard using a microscope.

Sensitivity Microcrystalline tests have high sensitivity; however, this method is best suited to pure and/or separated samples, since the presence of impurities, diluents, and adulterants can prevent or mask the formation of characteristic microcrystals

Ease of use These tests require intermediate to advanced expertise, as well as advanced knowledge for interpretation of results.

Thin-layer chromatography (TLC)

How it works This technique aims to analyze mixtures of chemicals by separating the compounds present. As part of the test, a stationary phase (usually a silica gel) is deposited over a glass or aluminum support, and mixtures of the sample are applied to it. After elution with an organic solvent, the different compounds will move upwards at different rates, allowing their separation.

Sensitivity TLC is less sensitive compared to Raman spectroscopy, mass spectrometry, and infrared spectrometry. It may be difficult to separate and identify novel substances using TLC, and it is not useful for separating complex mixtures. This technique is best used as a presumptive test with a fairly high degree of accuracy depending on sample purity

 Ease of use Relatively simple to use and interpret and is thus suitable for basic skill levels. However, intermediate and advanced skill levels are needed to interpret the results.

Spot/colour tests

How they work Spot/colour tests work based on the chemical reaction produced between analytes and indicators. The indicator reacts with the analyte to create a reaction that results in a certain colour staining. The results are then compared visually with reference charts.

Sensitivity These tests are considered presumptive, since they can only identify the presence or absence of a particular substance based on the test administered. A single test/reagent will only test for the presence or absence of a drug or class of drugs.

Ease of use Colorimetric tests can be performed with minimal training

Immunoassay

How it works This technique involves the binding of an antibody selective for the specific compound, creating an antibody-antigen complex that can be detecting methods such as fluorescence.

Sensitivity Immunoassay tests have high sensitivity within the microgram range; however, specificity is low due to a high false positive rate.

Ease of use Intermediate skill level for running the tests and result interpretation required.

Urine dipstick test

How it works This test is a presumptive test for fentanyl, and works via a chromatographic immunoassay.  In the presence of the specific analyte (fentanyl), a strip on the indicator stick appears or changes colour.

Sensitivity There is currently no data on fentanyl urine dipstick sensitivity

Ease of use Easy to use, with low skill level required for test administration and interpretation.

Ultraviolet spectroscopy

How it works UV spectroscopy analyses the intensity of light passing through a sample to create a characteristic spectrum and identify the substance.

Sensitivity This method has lower sensitivity, and has a higher rate of false positive results, since drugs with similar structures can yield the same UV spectra. It can be combined with chromatographic techniques for greater specificity.

Ease of use Low skill level is needed to run the test, while intermediate to advanced knowledge is required for the interpretation of results.