Time Lag Between Blood Estrogen and Urinary E1G
Urinary estrone-3-glucuronide (E1G) typically lags behind blood estradiol by approximately 24 hours (one full day), not just a few hours.
Evidence for the Time Lag
The research consistently demonstrates a one-day delay between peak blood estradiol and urinary E1G measurements:
Peak timing studies show that estrogen glucuronide peaks in urine are delayed mostly by 1 day compared to plasma estradiol peaks 1. This represents the time required for hepatic metabolism of estradiol to estrone, conjugation to E1G, renal filtration, and bladder accumulation.
In conceptional cycles, the defined rise in urinary E1G concentration occurred on average at Day LH-4.7 (range -3 to -6), while this represented changes that had already occurred in blood estradiol approximately 24 hours earlier 2.
The correlation studies between plasma estradiol and urinary E1G demonstrate that first morning urine E1G reflects the integrated estradiol production from the previous day 3. The correlation coefficient between urinary E1G and plasma estradiol was r = 0.60 (P < 0.001), with the understanding that urine represents a delayed, cumulative measure 3.
Clinical Implications of This Lag
This 24-hour delay has important practical consequences:
For ovulation prediction, the urinary E1G rise indicates events that occurred in the bloodstream approximately one day prior 4, 2.
First morning urine collection is preferred because it represents an integrated sample of hormone metabolism over the preceding 12-24 hours, providing a stable measure despite the inherent delay 3, 5.
The day-to-day coefficient of variation can be reduced from 40% to 25% by calculating ratios of glucuronides to creatinine, which helps account for urine concentration effects but does not eliminate the fundamental 24-hour lag 1.
Why the Full Day Lag Occurs
The physiological basis for this delay involves multiple steps: