Enzyme immunoassay of estriol in pregnancy urine

We describe an enzyme immunoassay for determination of total estriol in urine. Estriol covalently bound to horseradish peroxidase is used as tracer, and free and bound hormone are separated by precipitation with polyethylene glycol. The method can be used with either acid hydrolysis at 100 degrees C for 30 min or enzyme hydrolysis at 50 degrees C for 40 min; results by the former procedure are about 15% lower than results by the latter. Results were practically identical when we compared the enzyme immunoassay with a radioimmunoassay, using the same antiserum and method of hydrolysis. The day-to-day CV for three different concentrations was 10.7-12.0%, the within-series CV 6.6-8.6%. The additional time required for the enzyme reaction is compensated for by the rapid measurement of light absorbance. Thus this method is faster than radioimmunoassay when more than 25 samples are to be assayed.