Homogeneous enzyme immunoassay of estriol in picogram amounts

A homogeneous enzyme immunoassay for estriol has been described using estriol-glucose-6-phosphate dehydrogenase (E3G6PD) as enzyme conjugate. Antisera for estriol were raised by immunising rabbits with two different immunogens, estriol-6-(O-carboxymethyl oxime) bovine serum albumin (E36CMOBSA) and estriol-3-carboxymethyl ether bovine serum albumin (E33CMEBSA). A new method for preparation of estriol 3-O-carboxymethyl ether in high yield (90%) has also been described. Addition of anti-estriol antibodies to E3-G6PD conjugate resulted in inhibition of enzyme activity. In the presence of free estriol, the antibody induced inhibition of enzyme activity was reduced in a concentration dependent manner. The use of the heterologous combination between immunogen and enzyme conjugate, i.e. using anti-E33CMEBSA and E36CMOG6PD improves the sensitivity at the expense of specificity, the cross-reaction with other estrogenic hormone being 10-15%.