Non-invasive assessment of free steroid hormones: development of a high-throughput LC-MS/MS method for salivary steroid hormone quantification.

Steroid hormone concentrations reflect diverse physiological and pathological processes and have been recognized as valuable biomarkers for disease, with growing interest in their potential for patient stratification in precision medicine. Salivary steroid concentrations should reflect the free (biologically active) steroids in circulation, as steroids in the bloodstream passively diffuse to saliva. This allows for the direct measurement of free steroids without transporter protein-bound hormones (inactive form). However, implementation of salivary steroid quantification in larger studies remains limited by challenges associated with sample preparation. We began by reviewing the literature on relevant sample preparation approaches and identified commonly used 96-well solid phase extraction (SPE) methods for further evaluation. Three sample preparation methods were selected and assessed in terms of internal standard recovery and matrix effects, and their response was also compared using electrospray (ESI) versus UniSpray ionization (USI) liquid chromatography-tandem mass spectrometry (LC-MS/MS). We demonstrate a sensitive and rapid high-throughput method with Oasis HLB µElution SPE of 200 μL saliva in 96-well format and USI-LC-MS/MS for major steroids (testosterone, androstenedione, cortisone, cortisol, and progesterone) in saliva. The method achieved optimal recovery (77%), matrix effects (33%), and sensitivity with detection limits (MDL) ranging between 1.1 and 3.0 pg/mL and linearity (r(2) = 0.99). Intra-plate and inter-plate coefficient of variation (CV) was below 7% and 20% using USI. USI provided a higher (2.0-2.8-fold) response than ESI and higher signal-to-noise ratio (S/N). The method was then applied to 97 authentic saliva samples (41 male and 56 female) and significant correlations between age and BMI, and androgen levels were observed in both sexes. The proposed 96-well SPE USI-LC-MS/MS method is well-suited for determining steroid hormones in saliva with potential usefulness in large-scale studies and clinical settings.