State-of-the-Art of Serum Testosterone Measurement by Isotope Dilution-Liquid Chromatography- Tandem Mass Spectrometry

The recent interest of clinical laboratories in developing serum testosterone assays based on isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) stems from the lack of accuracy of direct immunoassays. In this study, we assessed the accuracy and state of standardization (traceability) of 4 published ID-LC-MS/MS procedures in a method comparison with an ID-gas chromatography (GC)-MS reference measurement procedure listed in the database of the Joint Committee for Traceability in Laboratory Medicine. The study used 58 specimens from different patient categories. Each specimen was measured in triplicate (ID-LC-MS/MS) and quadruplicate (ID-GC-MS) in independent runs. The testosterone concentrations by ID-GC-MS were 0.2-4.4 nmol/L (women), 0.2-2.0 nmol/L (hypogonadal man), and 10.1-31.3 nmol/L (normogonadal men). For ID-GC-MS, the CV was nearly constant, with a median of 1.0%; for ID-LC-MS/MS, it was concentration-dependent, with a median of up to 8%. Weighted Deming regression gave mean slopes, intercepts, and correlation coefficients of 0.90-1.11, -0.055-0.013 nmol/L, and 0.993-0.997, respectively. The % difference plot showed between 7% and 26% of the results outside a total error limit of 14%, with median deviations from ID-GC-MS between -9.6 and 0.4%. This study demonstrated fairly good accuracy and standardization of the tested ID-LC-MS/MS procedures. Performance differences between procedures were evident in some instances, due to improper calibration and between-run calibration control. This emphasizes the need for thorough validation, including traceability, of new ID-LC-MS/MS procedures.