How is it used?
Qualitative hCG testing is routinely used to confirm
pregnancy.
Quantitative hCG testing (also frequently called beta hCG), measures the actual amount of hCG present in the blood. It may be ordered to help diagnose an
ectopic pregnancy, to help diagnose and monitor a pregnancy that may be failing, and or to monitor a woman after a miscarriage. In addition, a quantitative hCG test may be ordered to diagnose trophoblastic disease or
germ cell tumors of the testes or ovary. It may be ordered at regular intervals to monitor the effectiveness of treatment for these conditions and to detect tumor recurrence.
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When is it ordered?
A
qualitative urine or blood hCG test is ordered as early as 10 days after a missed menstrual period if a woman wishes to confirm whether or not she is pregnant (some methods can detect hCG even earlier, at one week after conception). In certain patients, several
quantitative blood hCG tests over several days may be ordered to rule out an
ectopic pregnancy or to monitor a woman after a miscarriage. A doctor will also order a quantitative hCG test when she suspects trophoblastic disease or the presence of
germ cell tumors.
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What does the test result mean?
In non-pregnant women, hCG levels are normally undetectable. During early
pregnancy, the hCG level in the blood doubles every two to three days.
Ectopic pregnancies usually have a longer doubling time. Those with failing pregnancies will also frequently have a longer doubling time or may even show falling hCG concentrations. hCG concentrations will drop rapidly following a miscarriage. If hCG does not fall to undetectable levels, it may indicate remaining hCG-producing tissue that will need to be removed.
hCG is also used to monitor treatment in patients with trophoblastic disease and to detect recurrent disease after treatment is complete. During therapy, a falling hCG level generally indicates that the cancer is responding to treatment, while rising levels may indicate that the cancer is not responding to therapy. Increased hCG levels after treatment may indicate a recurrence of disease.
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Is there anything else I should know?
Tests performed too early in the
pregnancy, before there is a significant hCG level, may give
false-negative results, while blood or
protein in the urine may cause
false-positive results. Urine hCG tests may give a false negative result in very dilute urine. Patients should not drink large amounts of fluid before collecting a urine sample for a pregnancy test.
Certain drugs such as diuretics and promethazine (an antihistamine) may also cause false-negative urine results. Other drugs such as anti-convulsants, anti-parkinson drugs, hypnotics, and tranquilizers may cause false-positive results.
There are reports of false positive serum hCG results due to several different compounds (not drugs) that may interfere with the test. These include certain types of antibodies that may be present in some individuals and fragments of the hCG molecule. Generally, if results are questionable, they may be confirmed by testing with a different method.
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