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.

Bibliography

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Seckl, Michael J, Neil J. Sebire, and Ross S.
Berkowitz. "Gestational Trophoblastic Disease." Lancet
376.9742 (2010): 717–29. Print.

Sosolow, Robert A., and Teri Longacre,
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