Detection of hCG in trophoblastic disease. The USA hCG reference service experience

hCG is a glycoprotein hormone composed of two dissimilar subunits. This hormone is not only heterogeneous in peptide structure but also in combination of subunits and carbohydrate structure. Common hCG-related molecules include hCG, hyperglycosylated hCG, nicked hCG, hCG missing the beta-subunit C-terminal peptide, free alpha-subunit, free beta-subunit, nicked free b-subunit and urine beta-core fragment. This article discusses the structures these hCG-related molecules and their occurrences in early pregnancy, 7-week to term pregnancy, hydatidiform mole (preevacuation and postevacuation), persistent gestational trophoblastic disease, choriocarcinoma and other malignancies. Multiple serum hCG tests are evaluated, and their abilities to detect the multiple hCG-related molecules are investigated. The accuracy of different serum hCG tests in detecting hCG and hCG-related molecules in patients with gestational trophoblastic diseases is evaluated. The findings of persistent low hCG values in the absence of pregnancy or an identifiable malignancy are examined. In addition, the false positive hCG assay problem is discussed. False positive hCG tests have led to many incidences in which gestational trophoblastic disease has been erroneously diagnosed and needlessly treated. hCG tests are identified that give a disproportionate number of false positive results. Finally, guidelines are presented for selecting an hCG test.