For therapeutic drug monitoring, which methods are used for screening and confirmatory testing?

• A. Immunoassay for screening and HPLC for confirmation
• B. TLC for screening and GC-MS for confirmation
• C. GC-MS for screening and TLC for confirmation
• D. Immunoassay for screening and TLC for confirmation

Answer: (A)

In therapeutic drug monitoring, you want a quick, inexpensive screen to flag potential positives, followed by a highly specific confirmatory test to accurately quantify the drug. Immunoassays fit the screening role well because they can process many samples rapidly and at low cost, though they can show cross-reactivity that may cause false positives. For confirmation, you need a method with strong specificity and reliable quantification; high-performance liquid chromatography (HPLC) provides the needed separation of the drug from metabolites and accurate measurement, reducing the chance of misidentification. So pairing an immunoassay screen with HPLC confirmation reflects the practical two-step approach: fast initial screening, followed by a robust confirmatory test. The other options rely on less suitable screening methods or confirmatory choices, which don’t align as well with the typical workflow in therapeutic drug monitoring.