Enzyme immunoassay of estrogen-like substances in plasma, with polyethylene glycol as precipitant

We devised an enzyme immunoassay for plasma estrogen-like substances in pregnancy, using estriol covalently linked to horseradish peroxidase. Free and bound steroid were separated by use of polyethylene glycol reagent. The assay satisfies the normal criteria of specificity and precision. Results obtained by radioimmunoassay and enzyme immunoassay agreed well. Our assay is particularly applicable in smaller clinical laboratories to routine determination of plasma estriol in pregnancy.