Why both LC–MS/MS and FDA-compliant validation are essential for accurate estrogen assays?

Sensitive and accurate measurement of androstane-3β,17β-diol and androstane-3α,17β-diol in the circulation is important for clinical research and accurate clinical diagnosis. This report describes a highly sensitive, specific, precise and reliable assay for the simultaneous accurate measurement of serum androstane-3α,17β-diol and androstane-3β,17β-diol in postmenopausal women. The LLOQ of 1 pg/mL has been achieved with nicotinic acid derivatization, which is superior to picolinic acid by a factor of 5 to 10 in terms of signal to noise ratio. The difference is attributed to the higher acidity of picolinic acid which forms a more stable intermediate, thus decreasing derivatization efficiency. Potential interference from androstane-3α, 17α-diol, androstane-3β, 17α-diol, and 5-androstenediol has been well separated from the two target diols. The high level of specificity has been determined by well-developed chromatography and ion ratio monitoring. A good linearity in the range of 1 pg/mL to 200 pg/mL (0.03 pg to 6 pg on column) was obtained for both compounds at R > 0.998. The bias and coefficients of variation of all the QC levels are within the range of 10% while the recovery in both charcoal-stripped and unstripped human serum is around 85%. The matrix effect was evaluated and the results well met the acceptance criteria according to the guidelines of bioanalytical method development and validation. Using this newly developed method, the concentrations of both androstane-3α,17β diol and androstane-3β,17β diol were measured in normal postmenopausal serum, where the concentrations range from 2 pg/mL to 32 pg/mL for androstane-3α,17β diol and from 1 pg/mL to 10 pg/mL for androstane-3β,17β diol, respectively.