[Persistent low levels of human chorionic gonadotropin in the serum: investigation and management]

Persistent low levels of human Chorionic Gonadotropin-hCG, the pregnancy hormone, in the serum in the absence of pregnancy or any evidence of Gestational Trophoblastic Disease (GTD) is a diagnostic and therapeutic dilemma. This condition mostly presents during follow-up after patients with a history of GTD or hydatidiform mole or an incidental pregnancy test. Many physicians are not aware of the broad differential diagnosis of this condition which is mostly benign. Therefore, many women with this condition have received chemotherapy and hysterectomy for assumed malignancy which were ineffective and unwarranted. The most common etiologies are: 1. Pituitary hCG: A condition mostly found in older women, completely benign and can be resolved using hormone replacement therapy or oral contraceptives. 2. False positive hCG: this condition has no clinical meaning, it can be identified by the absence of hCG in a parallel urine sample or using a better hCG test with no past reports of false positive. 3. Quiescent GTD: This is a benign trophoblastic disease in which the hyperglycosylated hCG accounts for a small percentage of the total hCG in the serum. Due to its premalignant nature, a follow-up of the hCG levels and the hyperglycosylated hCG percentage is needed. The hCG molecule has many forms. Different hCG tests detect different forms identified as heterogeneous in nature. For each etiology mentioned above there is a characteristic dominant form. If it was known which test to use, the diagnosis could be made.