Sensitive and Specific Assay for Human Chorionic Gonadotropin (hCG) Based on Anti-Peptide and AntihCG Monoclonal Antibodies: Construction and Clinical Implications*

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Abstract
We developed a highly sensitive and specific assay for hCG using monoclonal antibodies (Mabs) directed against a 37-amino acid synthetic polypeptide analogous to the carboxyl-terminusCTP) of βShCG. Five antibodies that varied by either their affinity for βShCG or their specificity for epitopes on CTP were investigated. To measure hormone levels, we used as the radiolabeled indicator an a-subunit-reactive Mab. The monoclonal-immunoradiometric assay had a lower limit of sensitivity of 0.05 ng/ml. Serum levels of hCG or hCG-like material with CTP structure were measured in 229 healthy blood donors; 1.1% of healthy men and 4.6% of nonpregnant women younger than 50 yr had serum values varying between 0.05 and 0.23 ng/ ml. Moreover, 6 of 7 healthy women older than 50 yr had detectable levels in the 0.05-0.20 ng/ml range. To study the disappearance rates in normal women, we followed serum hCG serum levels of 6 women who had previously received a single im injection of the hormone. These individuals failed to develop a pregnancy after in vitro fertilization; hCG declined from 0.5 to 0.05 ng/ml within 2 weeks. These results were in contrast to the findings in 12 patients with hCGproducing tumors. In 9 patients without any evidence of recurrent disease, hCG levels became undetectable within 5 months. However, 3 others had levels consistantly above 0.05 but below 0.5 ng/ml. In 2 of these three patients, subsequent increasing hCG levels were associated with tumor recurrence. We conclude that this hCG assay based on both anti-peptide and anti-hCG Mabs may be useful in tumor monitoring. {J Clin Endocrinol Metab63: 1319, 1986

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