Understanding Your Beta-hCG Test in GTD

The beta-hCG test is the common pregnancy test. It’s the same one that’s used in the doctor’s office as either a blood or urine test. It is also used in the urine stick tests that are available in most drug stores. All of these tests can determine the presence of the hCG protein. This protein is produced by the placenta. Therefore, it is a diagnostic test for pregnancy.

Since GTD is a tumor of the placenta, these abnormal placental cells make a lot of the hCG protein. So this test can serve as an excellent tumor marker. It can show whether the tumor is responding to treatment or whether the disease is progressing. It is almost the perfect tumor biomarker.

Once the diagnosis of GTD is made, the hCG test has many important roles in managing your disease. For example:

  • It is used in determining stage and prognosis of the disease.
  • It helps monitor response to treatment.
  • It is used to determine the need for treatment after evacuation of a molar pregnancy.
  • It is used to determine failure of treatment or need to change treatment.

hCG Testing after Evacuation of a Molar Pregnancy

The most useful hCG test is called a quantitative hCG test. It is performed on a blood sample. This test determines the actual amount of hCG protein in your blood at the time the blood is drawn. Expected ranges at the time of diagnosis is usually somewhere within 10,000 IU/L – 1,000,000 IU/L or more. After the molar pregnancy is removed, this test is often done every 1-2 weeks until it is negative.

Follow-up after the hCG becomes normal is very important. So this test is done every month for at least 6 months to one year after the diagnosis is made. Any change or rise in the hCG in that period suggests recurrent GTD disease. The exception to that is when a normal pregnancy occurs. However, pregnancy during this surveillance time is NOT a good idea. Using birth control is highly recommended.

hCG as a Marker of Invasive or Metastatic Disease

A rise or plateau of hCG level during the follow up period after treatment suggests invasive or metastatic disease. If the test value rises three weeks in a row, then the doctor should search for metastatic disease. This is also the case if the hCG test stays at the same level for three weeks or more. Chemotherapy is usually needed at this time for treatment.

hCG as a Marker of Treatment Failure

The hCG test should continue to decrease after surgical therapy—hysterectomy—or chemotherapy for invasive or metastatic GTD. The test is done prior to each chemotherapy treatment. After a hysterectomy it’s done every 1 to 2 weeks. If the test number rises or stays the same over 2 treatments, your doctor is likely to change your treatment.

The “not so perfect” hCG test

The quantitative hCG test is often the only test used to monitor resolution of GTD. The test is not perfect, though. There are several possible hCG results that don’t quite fit the clinical picture. When there is possible confusion, your doctor may ask a specialty lab to check for other molecules closely related to hCG. The lab will also check for molecules that interfere with hCG. In general, it’s rare that hCG tests are difficult to interpret. But when they are, there are several situations that are likely to be the issue:

  • Phantom hCG. Sometimes a woman develops antibodies that react to the hCG test. These antibodies produce a false positive blood test. The antibodies are not secreted whole in the urine. So a quick way to determine if this is the case is to also check a urine pregnancy test. If the urine test is negative, then it is likely that the blood test is a false positive test and does not indicate GTD.

  • Quiescent GTD. A persistent low level of hCG that does not respond to treatment with surgery or chemotherapy suggests quiescent GTD. There is a time when the abnormal placental cells stop growing. They therefore produce little hCG. Chemotherapy works best when cells are growing. So the treatment has little effect. Most cases of quiescent GTD will go away over 1-2 years. It is important to follow hCG blood tests monthly. That’s because in about 10 to 20 percent of the cases, active disease will develop. Then chemotherapy is needed. Special tests to look at other related molecules of hCG will help make this diagnosis.

  • Placental Site Trophoblastic Tumor (PSTT). These tumors are very rare tumors. They consist of a type of trophoblastic cell in the placenta called intermediate trophoblastic cells. These do not produce a lot of hCG. Therefore these tumors can be difficult to detect. They also do not respond to chemotherapy. In cases that have low levels of hCG in the blood, a special test for a related hCG molecule called free-beta hCG can be done. If the hCG molecule is made up of a large portion of the free-beta molecule, then PSTT is suspected. This free-beta test is also elevated in other cancers that produce hCG from the actual tumor. For example, lung cancer or cervical cancer will do this. The hCG in these cases is not anyway related to GTD.