Analysis of Testosterone Esters in Serum and DBS Samples—Results From an Interlaboratory Study

Testosterone (T) formulations that are used for doping purposes often contain the steroid in esterified forms. As these esters are hydrolysed in the bloodstream before renal excretion, they can be detected in blood matrices and have not been detected in urine so far. Serum samples can additionally be used for longitudinal blood steroid profiling, but their collection, shipping and storage have some disadvantages. The use of dried blood spots (DBS), an alternative blood matrix, is more convenient for pre-analytical and post-analytical aspects but is not fully established in antidoping laboratories yet. To evaluate the ability of multiple antidoping laboratories to detect T-esters in serum and DBS samples, an interlaboratory study was organised. Common T-esters were spiked in five samples of each matrix (serum, cellulose card DBS, polymeric DBS) at concentrations that correspond to an administration scenario and sent as blinded specimens to each laboratory. The laboratories were requested to apply their own analytical method to detect the T-esters and to provide a rough estimate of their concentrations. All laboratories identified the spiked testosterone esters correctly in all samples and the estimated concentrations were deemed comparable (average relative standard deviation < 30%), considering that only qualitative initial testing procedures (ITPs) were used. This study could firstly demonstrate the capability of different analytical approaches to analyse T-esters in serum and DBS samples and, secondly, show that the methods employed by the participating laboratories are all fit for purpose.