Endocrine Abstracts

Introduction: The quality of testosterone assays has been a matter of debate for several years. Known limitations of testosterone immunoassays are the cross-reactivity with other steroids and a high variation in the low concentration range. We hypothesized that one of the additional limitations of testosterone immunoassays is an ineffective displacement of testosterone from its binding protein.

Methods: Thirty samples from women not using oral contraceptives (OAC), 30 samples from women using oral contraceptives, and 30 samples from pregnant women were used to measure testosterone by an ID-LC-MS/MS method and by six commercially available testosterone immunoassays (Unicel, Architect, Centaur, Cobas, Immulite and Liaison). In addition, SHBG was measured by immunoassay (Architect).

Results: The 1st generation immunoassays (Unicel, Centaur, Immulite and Liaison) showed inaccurate testosterone results in the method comparisons with the ID-LC-MS/MS method (R between 0.61 and 0.86) and for some assays (Unicel and Liaison) also a very poor standardization (slopes of 0.59 and 0.67, respectively). On average, SHBG concentrations were lowest in women not using OAC and highest in pregnant women and overall ranged from 18.5 to 633 nmol/l. In the 1st generation immunoassays, but not in the 2nd generation immunoassays, we observed an inverse relationship between SHBG concentrations and deviations in testosterone from the ID-LC-MS/MS results.

Conclusion: First generation testosterone immunoassays are influenced by SHBG concentrations which leads to inaccurate results in samples from subjects with high or low SHBG concentrations, respectively. Laboratory specialists, clinicians, and researchers should be aware of this limitation in 1st generation testosterone immunoassays which are still used worldwide.