A-075 Comparability of Free Testosterone Measurements- Results of the Interlaboratory Study

Abstract Background Assessment of free testosterone (FT) has been recommended as a biomarker for diagnosis and management of hypogonadism and female hyperandrogenism. Reliable laboratory measurements are essential for correctly diagnosing and treating these diseases. FT is currently measured using direct commercial immunoassays, assays employing equilibrium dialysis (ED) or other separation techniques, or it is estimated by calculating free testosterone (cFT). There are concerns about the accuracy and reliability of current methods that may impact patient care. To obtain more information about variability of FT measurements used in patient care, CDC’s Clinical Standardization Programs (CDC CSP) conducted an interlaboratory comparison study. Methods CDC CSP developed an accurate, automated method using ED coupled with isotope dilution ultra-high-performance liquid chromatography tandem mass spectrometry (ED-UHPLC-MS/MS). The ED step follows an internationally recognized procedure. The method is calibrated with primary reference material (National Measurement Institute-M914) and was used to assign target values to sera used in the study. The FT concentrations ranged from 3 to 339 pg/mL. In the interlaboratory comparison study single-donor serum samples were provided to participants operating FT methods used in patient care. The participating methods included commercially available platforms utilizing Chemiluminescence Immunoassay or radioimmunoassay techniques, as well as laboratory-developed assays using ED-LC-MS/MS. Results Preliminary findings of the CSP interlaboratory comparison study found large variability among participating assays. The agreement among IA and among ED-LC-MS/MS assays was close. However, FT concentrations obtained by IAs were in average 6 times lower compared to the ED-LC-MS/MS methods. Results estimated using the Vermeulen equation overestimated FT in average by 15% compared to the ED-LC-MS/MS methods and by over 6 times compared to IAs. Conclusions Large variability is observed between FT laboratory developed tests (LDTs) and IAs. As both LDTs and IAs are used in patient care, standardization of FT measurements to assure better patient care is needed. CDC CSP is addressing the need by developing highly accurate and precise FT method and conducting an interlaboratory comparison studies that can aid with improvement of the agreement among assays and identifying potential factors causing differences among assays.