Quantitative determination of human chorionic gonadotropin by enzyme linked immunosorbent assay

Abstract

Human chorionic gonadotropin(HCG) has been used as a universal marker in the diagnosis of pregnancy and as a therapeutic marker during the clinical treatment of trophoblastic disease patients. A number of sensitive and specific methods have made the HCG assay a useful tool in the laboratory as well as in the clinical fields. We attempted to develop a sensitive, convenient ELISA method of determining HCG, applicable to clinical fields. Subunits of HCG were isolated by an ion exchange chromatography and three protein peaks were obtained. Antisera against $\alpha$-HCG and $\beta$-HCG were raised in rabbits and antibodies were purified by an affinity chromatography on whole HCG-Sepharose 4B. These purified antibodies were tested for reactivity with $\alpha-, \beta-$ and whole HCG and for cross-reactivity with three other analogous hormones, i.e., FSH, TSH, LH. Anti $\alpha$-HCG strongly cross-reacted with these hormones. Anti $\beta$-HCG reacted specifically with $\beta-$ and whole HCG but not with $\alpha$-HCG. Moreover the anti $\beta$-HCG didn``t show any cross-reactivity with FSH, LH or TSH. Using the double antibody sandwich ELISA method, HCG levels were determined in the sera of 20 women with malignant trophoblastic diseases. A standard curve showing a lineality up to $10 \mu{g}$HCG/ml was obtained by the ELISA method. The sensitivity was calculated to be 40mIU/ml. When the ELISA values were compared with those of RIA, the two methods were shown to be significantly correlated with each other.