What is the reference method for therapeutic drug monitoring (TDM) and HbA1c measurement?

• A. Semiquantitative drug screening test
• B. GC-MS
• C. HPLC
• D. TLC

Answer: (C)

High-performance liquid chromatography (HPLC) is the reference method because it provides precise, reproducible quantitation and reliable separation of analytes. For HbA1c, HPLC separates glycated hemoglobin from other forms, allowing accurate, standardized reporting across laboratories. In therapeutic drug monitoring, validated HPLC methods offer robust quantitation for many drugs and form part of the accepted reference approach in routine labs, even though for some drugs GC-MS or LC-MS/MS may be used for higher sensitivity or specificity. Semiquantitative screening lacks the quantitative accuracy required for a reference method, and thin-layer chromatography does not meet modern standards for precision and standardization in TDM or HbA1c measurement.