What is human chorionic gonadotropin (HCG)?
Gestational trophoblastic disease: Gestational trophoblastic disease (GTD) includes several types of tumors, including hydatidiform mole and choriocarcinoma. These tumors develop because of an anomaly in pregnancy when placental (trophoblastic) cells grow out of control. Hydatidiform moles can progress to choriocarcinomas, which are generally aggressive and, if left untreated, tend to metastasize widely. hCG is elevated in almost all patients with trophoblastic tumors and is a useful diagnostic marker for monitoring treatment. Gestational trophoblastic disease can be diagnosed and followed by measuring hCG hormone levels in the blood and urine. Ultrasound, computed tomography (CT), positron emission tomography (PET), or magnetic resonance imaging (MRI) scans can also be used to look for tumors. However, when scans show no evidence of tumor presence, hCG levels are often relied on to determine whether the disease may be present.
hCG as a diagnostic marker: hCG is used as a diagnostic indicator of tumor formation in gestational trophoblastic disease because of an association between elevated hCG levels and trophoblastic tumors as well as nonseminomatous testicular tumors. Trophoblast-derived tumors often secrete only the free beta-hCG subunit. Diagnostic assays that are specific for the free beta-HCG subunit are most useful for monitoring tumor development and progression. A negative result is generally less than 5 milli international units/milliliter (mIU/ml) of beta-hCG in the blood. Gestational trophoblastic disease is treatable, and hCG levels can be used to monitor the success of treatment, in that as the tumor decreases, so does the level of hCG. In some cases, elevated hCG levels may be due to factors other than gestational trophoblastic disease. Certain hormones and proteins in the blood may interfere with the blood test results; therefore, hCG tests should be performed on both the blood and the urine in the diagnosis of gestational trophoblastic disease.
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