Human chorionic gonadotropin (hCG) is a near-perfect biochemical marker for pregnancy. Serial measurements of hCG assist in the differentiation of normal from abnormal gestational events, and sensitive home tests are easy for the lay public to perform and interpret. No test is perfect, however, and providers must understand how to interpret unexpected hCG results. Differential diagnosis must address problems inherent to the test itself (heterophile antibody reactions), abnormal hCG production (from neoplastic trophoblastic or nontrophoblastic tissues), and physiologic hCG (menopausal pituitary) production. Patient history of pregnancy, past gestations, menstrual cycles, and cancer can point to the most likely diagnostic category. Often more sophisticated testing of hCG variants will be required, such as determination of the percentage of hyperglycosylated hCG as a marker of invasive trophoblastic disease (choriocarcinoma) or measured ratio of the free β subunit as a marker of nongestational malignancy. Consultation with clinical and laboratory experts will ensure appropriate and safe clinical management. In the case presented, active papillary thyroid carcinoma was identified in a woman whose age was appropriate for perimenopause. Secretion of small amounts of hCG by the tumor itself was possible but statistically unlikely. Increased follicle-stimulating hormone concentration confirms menopause, and treatment of the cancer should not be delayed.
Grant/funding Support: None declared.
Financial Disclosures: None declared.
- © 2008 The American Association for Clinical Chemistry