What happens if you tested positive on initial screening? Is it over now? Not yet. There are many reasons to suspect a false-positive result, which can be due to taking prescribed or over-the-counter medications, human error, etc. Each positive screening should undergo a confirmatory test, which is more sensitive and precise.

One of the most popular confirmatory test is GC/MS – Gas chromatography/ Mass Spectrometry. This test presents a combination of two analytical techniques, and because of the specific procedure it requires and high costs of it, is always used either for confirmatory tests or for forensic tests for court orders. Unlike drug screens, GC/MS not only detects the drugs presented in a sample, but also measures the quantity, normally in nanograms. This test is effective on all biological fluids, which is very important since blood levels of certain drugs indicate the actual level of intoxication, whereas urine testing cannot determine that.

GC/MS test works by mixing a sample with organic solvent, which is then evaporated in order to concentrate the drug presence. Gas chromatography forces helium (or other gas) through a thin tube layered with silicone polymer by which the drugs are being separated. Once the drug metabolites have been separated, mass spectrometry identifies the substance – a molecule of certain drugs always break down to unique fragments, always the same, and is compared to a computer library. A 98% match is considered a confirmation of a positive test result. This kind of testing is very precise and not only confirms that presence of toxins in a sample, but also gives an accurate estimate of the levels of any certain substance.