Determination of testosterone by liquid Chromatography–Tandem mass spectrometry in dried plasma obtained from capillary blood using the HealthID PSD microsampling device

Monitoring testosterone (T) levels is essential in various clinical contexts, but traditional venous sampling is invasive and limits access. This study describes the development and validation of a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to quantify T in dried plasma spot (DPS) samples obtained from capillary blood using the HealthID PSD microsampling device. A chloride-based correction of plasma volume in the DPS and a multiplication factor were applied to estimate venous plasma concentrations. The method showed linearity from 1.63 to 104.02 nmol/L, with accuracy ranging from 96.8 % to 105.2 % and precision between 1.90 % and 7.24 %. Matrix effects were adequately corrected by the internal standard, and extraction yield exceeded 89 %. T in DPS samples was stable for up to 10 days at room temperature and 40 °C. Clinical validation involved 104 volunteers, including cisgender men and transgender individuals on hormone therapy. A strong correlation was observed between DPS-derived and venous plasma testosterone levels (r = 0.950), and the percent total error (TE%) of 16.41 % met the desirable performance criterion derived from biological variation data. The method proved robust against hematocrit variation and sample volume differences. This is the first report on T quantification using a capillary plasma separation device, highlighting the potential of the HealthID PSD for simplified, decentralized T monitoring. The approach offers practical advantages in collection, transport, and storage, making it a promising alternative to conventional phlebotomy for clinical applications.