Which follow-up test is best for verifying common drug screening results?

Gas chromatography/mass spectrometry (GC/MS) is recognized as the gold standard for verifying the results of common drug screenings. This method provides a high degree of specificity and sensitivity, which is crucial in confirming the presence of drugs previously indicated by initial screening tests.

The reason GC/MS is the best follow-up test is due to its ability to separate and identify chemical compounds in a mixture. Mass spectrometry allows the analysis of the unique mass-to-charge ratios of ions which is extremely effective in distinguishing between substances that may have similar chemical structures. This precision ensures that false positives or negatives from the initial screening tests can be rectified, providing more reliable results.

Other methods, such as enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay, are primarily used for initial screenings and are less specific than GC/MS. They can sometimes produce cross-reactivity, leading to inaccurate results. Thin-layer chromatography can also be used for drug analysis, but it does not offer the same level of sensitivity and specificity as GC/MS, making it less suitable for confirmation purposes.

Therefore, the use of gas chromatography/mass spectrometry in confirming drug tests is essential in clinical settings and toxicology due to its accuracy and reliability.