A Liquid Chromatography-Mass Spectrometry Method for the Simultaneous Measurement of Fifteen Urinary Estrogens and Estrogen Metabolites: Assay Reproducibility and Inter-individual Variability
Source: Cancer Epidemiol Biomarkers Prev. 2008 December ; 17(12): 3411–3418. doi: 10.1158/1055-9965.EPI-08-0355. RT Falk1, X Xu2, L Keefer3, TD Veenstra2, and RG Ziegler1
Abstract
Background—Accurate, reproducible, and sensitive measurements of endogenous estrogen exposure and individual patterns of estrogen metabolism are needed for etiologic studies of breast cancer. We have developed a high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to quantitate simultaneously 15 urinary estrogens and estrogen metabolites (EM): estrone (E1); estradiol (E2); three catechol estrogens; five estrogens in the 16α pathway, including estriol (E3); and five methoxy estrogens.
Methods—Overnight urines were obtained from 45 participants. For the reproducibility study, two blinded, randomized aliquots from 5 follicular and 5 luteal premenopausal women, 5 naturally postmenopausal women, and 5 men were assayed in each of four batches. Assay coefficients of variation (CVs) and intraclass correlation coefficients (ICCs) were calculated with analysis of variance models. Data from the additional 25 participants were added to compare EM levels by menstrual/sex group and assess inter-individual variability. Results—For each EM, overall CVs were ≤10%. ICCs for each menstrual/sex group were generally ≥98%. Although geometric mean EM concentrations differed among the four groups, rankings were similar, with E3, 2-hydroxyestrone, E1, E2, and 16-ketoestradiol accounting for 60–75% of total urinary EM. Within each group, inter-individual differences in absolute concentrations were consistently high; the range was 10–100 fold for nearly all EM.
Conclusion—Our LC-MS/MS method for measuring 15 urinary EM is highly reproducible, and the range of EM concentrations in each menstrual/sex group is quite large relative to assay variability. Whether these patterns persist in blood and target tissues awaits further development and application of this method.