At a Glance
Why Get Tested?
To confirm and monitor pregnancy or to diagnose trophoblastic disease or germ cell tumours
When to Get Tested?
As early as 10 days after a missed menstrual period (some methods can detect hCG even earlier, at one week after conception) or if a doctor thinks that your symptoms suggest ectopic pregnancy, a failing pregnancy, trophoblastic disease or germ cell tumours
Sample Required?
A urine sample collected first thing in the morning or a blood sample taken from a vein in the arm
The Test Sample
What is being tested?
hCG is a protein produced in the placenta of a pregnant woman. A pregnancy test is a specific blood or urine test that can detect hCG and confirm pregnancy. This hormone can be detected 10 days after a missed menstrual period, the time period when the fertilised egg is implanted in the woman's uterus. With some methods, hCG can be detected even earlier, at one week after conception.
During the early weeks of pregnancy, hCG is important in maintaining function of the corpus luteum (the mass of cells that forms from a mature egg). Production of hCG increases steadily during the first trimester (8 - 10 weeks), peaking around the 10th week after the last menstrual cycle. Levels then fall slowly during the remainder of the pregnancy. hCG is no longer detectable within a few weeks after delivery. hCG is also produced by some germ cell tumours and increased levels are seen in trophoblastic disease.
How is the sample collected for testing?
hCG is commonly detected in urine. The preferred specimen is a random urine sample collected first thing in the morning. hCG can also be measured in blood taken from a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
The Test
How is it used?
Qualitative (reported as positive or negative) hCG testing is routinely used to confirm pregnancy. Quantitative (reported as a number) hCG testing (also called beta hCG) measures the actual amount of hCG present in the blood. It may be used to help diagnose an ectopic pregnancy, to help diganose and monitor a pregnancy that may be failing, and to monitor a woman after a miscarriage. In addition, a quantitative hCG test may be used to diagnose trophoblastic disease or germ cell tumours of the testes or ovary. It may also be used at regular intervals to monitor the effectiveness for these conditions and to detect tumour recurrence.
When is it requested?
A qualitative urine or blood hCG test can be done 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 requested to rule out an ectopic pregnancy or to monitor a woman after a miscarriage. A doctor will also request a quantitative hCG test if they suspect trophoblastic disease or the presence of germ cell tumours.
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 a tumour is responding to treatment, while rising levels may indicate that a tumour is not responding to therapy. Increased hCG levels after treatment may indicate a recurrence of disease.
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 tranquilisers 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.
Common Questions
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Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
