Negative Pregnancy Test in Patients with Trophoblastic Diseases

Abstract

Quantitative and qualitative human chorionic gonadotrophin (hCG) assays are widely used to detect pregnancy state and abnormal trophoblastic lesions. At least five different forms of hCG have been characterized and different trophoblastic diseases produce different forms of hCG in varying proportions. Because of the difference in antibody specificity in various commercial automated immunoassays of HCG, discordant results may be obtained by laboratories using different hCG assays, with a falsely low or negative result obtained if the assay does not recognize the hCG variants produced from the trophoblastic tissue. On the other hand, significantly elevated hCG concentration can paradoxically lead to false-negative results in two-site immunometric assay due to high-dose hook effect. Clinicians managing patients with trophoblastic lesions should be aware of these limitations of current hCG assays and clinical laboratories should have measures to avoid analytical false negative hCG results.