Any credible drug screening program will involve a two-step process. Initial (immunoassay) and confirmatory (gas chromatography-mass spectrometry [GC-MS]) testing are the methods most commonly utilized to test for drugs. Using a combination of both tests allows a high level of sensitivity and specificity, meaning there is an extremely low chance for false positives or false negatives.4
The immunoassay is performed first and is often used as a screening method. If the immunoassay is negative, no further action is required, and the results are reported as negative. If the sample is positive, an additional confirmatory GC-MS analysis is performed on a separate portion the biological sample.