Association of estrogen measurements in serum and urine of premenopausal women

We evaluated conjugated and unconjugated urinary estrogen metabolites as surrogate biomarkers for serum levels of unconjugated E1 and E2 in premenopausal women.Repeated blood and urine samples were analyzed for estrogens and their metabolites using radioimmunoassays and liquid chromatography/mass spectrometry.The strongest correlation (r = 0.39) was observed between serum E1 and urinary E1 and E2. The correlations of urinary E2 (r = 0.35), E1 (r = 0.29), all E2 metabolites (r = 0.30), all E1 metabolites (r = 0.23) and total estrogens (r = 0.26) with serum E2 were only moderate although statistically significant. All correlations were substantially stronger for Whites than Asians.Urinary E2 emerged as the best predictor for serum E1 and E2, but the large intra-subject variability in urinary estrogen levels limits its use as a biomarker.