Comparison of estrone and estradiol measurements by LC-MS/MS and RIA. The top graphs compare levels of total and unconjugated estradiol measured by LC-MS/MS (y axis) to estradiol measured by RIA (x axis). The two leftmost graphs on the bottom compare levels of total and unconjugated estrone (by LC-MS/MS), respectively, to estrone (by RIA); the rightmost bottom graph compares total estrone (LC-MS/MS) to estrone sulfate (RIA). All axes are logarithmically scaled. LC-MS/MS, liquid chromatography tandem mass spectrometry; RIA, radioimmunoassay.