4-Hydroxyestradiol, Urine Creatinine Ratio Unit Converter

4-Hydroxyestradiol (4-OH-E2) is a metabolite of estradiol, the body's primary estrogen. It is produced when the enzyme CYP1B1 hydroxylates estradiol at the C-4 position during Phase I liver metabolism.

Estrogen is metabolized through three competing pathways: 2-hydroxylation (generally protective), 4-hydroxylation (potentially genotoxic), and 16α-hydroxylation (proliferative). Under normal conditions, about 60–80% of estrogen flows through the 2-OH pathway, while only about 7–11% goes through the 4-OH pathway.

The urine creatinine ratio normalizes 4-OH-E2 concentration against urinary creatinine to account for differences in hydration. This provides a consistent measure of 4-OH-E2 excretion regardless of how dilute or concentrated the urine sample is.

4-OH-E2 is produced primarily in the liver when the enzyme CYP1B1 hydroxylates estradiol. CYP1B1 is also expressed in breast tissue, uterine tissue, and adipose tissue, where local production of 4-OH-E2 can occur.