A radioimmunoassay has been developed for the measurement of unconjugated oestradiol in urine. After extracting with ether and purifying by thin layer chromatography, the assay is performed using anti serum prepared against oestrone 17 oxime bovine serum albumin conjugate. Dextran coated charcoal is used to separate free and bound fractions. The measureable range on the standard curve is from 10 to 1000 pg. The blank of the method is 9.7 ± 3.6 pg (SD) and is independent of urine volume. The intra assay coefficient of variation is 9.5% and the inter assay variation is 12.8%. The accuracy and specificity of the method are also satisfactory. During one menstrual cycle, urinary free oestradiol averaged 32 ng/day (n=9, range 22 to 58) during the follicular phase; 341 ng/day at the midcycle peak; and 46 ng/day (n=10, range 12 to 138) during the luteal phase. The oestradiol content of 3 consecutive 24 hr urines from a normal man was 4.8 ng/day (2.7 to 7.2).
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