False-positive hCG by enzyme immunoassay resulting in repeated chemotherapy.
BACKGROUND: In abnormal pregnancies, it is necessary to follow hCG levels to ensure resolution of the pregnancy, either spontaneously or after therapy. Lack of a normal resolution can be treated with methotrexate. CASE: A 32-year-old woman had a persistently elevated serum hCG level analyzed by enzyme immunoassay technique before and after being treated with three courses of methotrexate. Analysis of the serum samples by radioimmunoassay technique gave negative results. CONCLUSION: If the expected laboratory response is not forthcoming in the treatment of an abnormal pregnancy with methotrexate, hCG analysis by another assay method is recommended. False-positive hCG levels can result from the presence of heteroantibodies in the serum of the patient.