An isotope dilution-liquid chromatography-tandem mass spectrometry-based candidate reference measurement procedure...

This study presents a candidate reference measurement procedure (RMP) for testosterone quantification in human serum and plasma, utilizing isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC MS/MS).

The developed LC-MS/MS method employs a two-dimensional heart-cut LC approach combined with solid-phase extraction (SPE) for sample clean-up, ensuring accurate testosterone analysis in human serum and plasma. Traceability to SI units was achieved by using a primary reference material listed by the Joint Committee on Traceability in Laboratory Medicine (JCTLM). An alternative quantification approach using qNMR content determination is also described. Assay validation followed current guidelines, assessing selectivity and specificity with spiked serum samples. Matrix effects were evaluated through post-column infusion experiments and comparison of standard line slopes. Precision, accuracy, and trueness were determined through an extensive 5-day protocol. Measurement uncertainty for reference value assignment was evaluated as per the Guide to the Expression of Uncertainty in Measurement (GUM), with three individual sample preparations performed on at least two different days.

The RMP facilitated testosterone quantification in the range of 27.7 pmol/L (8.00 pg/mL) to 62.4 nmol/L (18.0 ng/mL) without interference from structurally-related compounds or matrix effects. Intermediate precision was ≤3.1 % and repeatability ranged from 1.4 to 1.9 % across all analyte concentrations. The bias ranged from -1.2 to 3.0 % for all levels and matrices. Expanded measurement uncertainties (k=2) for single measurements (n=1) ranged from 3.4 to 6.4 %. Measurement uncertainties for target value assignment (n=6) were ≤1.5 %, with expanded uncertainties ≤2.9 % (k=2) for all levels. Specific assessment at the LLMI yielded an expanded uncertainty (k=2) of 4.4 % for target value assignments (n=6), confirming the method's suitability for accurate and precise quantification over the entire measuring range.

The RMP demonstrated high analytical performance for testosterone quantification in human serum and plasma, making it suitable for routine assay standardization and clinical sample evaluation.