Assay reproducibility and interindividual variation for 15 serum estrogens and estrogen metabolites measured by liquid chromatography-tandem mass spectrometry.

Fuhrman BJ1, Xu X2, Falk RT3, Dallal CM3, Veenstra TD2, Keefer LK4, Graubard BI3, Brinton LA3, Ziegler RG3, Gierach GL3.

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Abstract

BACKGROUND:

Interindividual differences in estrogen metabolism may partially account for differences in risks of estrogen-responsive cancers. We conducted a proof-of-performance study to assess the reproducibility of a LC/MS-MS method for measurement of 15 serum estrogens and metabolites (all 15 termed EM) in total (conjugated+unconjugated) and unconjugated forms and describe interindividual variation.

METHODS:

Interindividual variation in serum EM profiles was evaluated for 20 premenopausal women, 15 postmenopausal women, and 10 men. Replicate aliquots from 10 premenopausal women, 5 postmenopausal women, and 5 men were assayed eight times over 4 weeks. Components of variance were used to calculate coefficients of variation (CV) and intraclass correlation coefficients (ICC).

RESULTS:

In postmenopausal women and men, median EM concentrations were similar and substantially lower than that in premenopausal women. Within each sex/menopausal group, the sum of all EM varied 5- to 7-fold across extreme deciles. Some EM had greater variation; total estrone varied approximately 12-fold in premenopausal and postmenopausal women. Unconjugated estradiol varied 17-fold in postmenopausal women but only 5-fold in premenopausal women and men. CVs reflecting variation across replicate measures for individuals were <5% for most EM, but higher in some individuals with a low EM concentration. Overall laboratory CVs for all but one EM were <2% and ICCs were >99% for all EM in each group.

CONCLUSIONS:

The serum EM assay has excellent laboratory reproducibility. In premenopausal women, postmenopausal women, and men, interindividual variation in EM measures is substantially greater than laboratory variation.

IMPACT:

The serum EM assay is suitable for epidemiologic application. See all the articles in this CEBP Focus section, "Biomarkers, Biospecimens, and New Technologies in Molecular Epidemiology."