Also known as: pregnancy test, qualitative hCG, quantitative hCG, beta hCG
Name: human chorionic gonadotrophin
Related tests: Maternal AFP
Why is the test done?
To confirm and monitor a pregnancy or to diagnose trophoblastic disease or germ cell tumours.
When is it done?
When a period is ten days late (some methods can detect hCG earlier, one week after conception) or when there are symptoms suggesting ectopic pregnancy, miscarriage, trophoblastic disease or a germ cell tumour.
What samples are required?
A first-morning urine sample or a blood sample taken from a vein.
What is being analysed?
hCG is a protein produced by the placenta during pregnancy.
The pregnancy test is a specific test, carried out on a blood or urine sample, that can measure hCG and confirm a pregnancy.
This hormone can be detected when a period is ten days late, as this is the time the fertilised egg needs to implant in the uterus. With some methods hCG can be measured earlier, one week after conception.
During the first weeks of pregnancy hCG plays a key role in maintaining the function of the corpus luteum (the mass of cells left behind after the mature egg is released).
hCG production rises steadily during the first trimester (8-10 weeks) and peaks around the 10th week after the last menstrual period. hCG levels then fall slowly over the following weeks of pregnancy and are no longer detectable a few weeks after delivery.
hCG is also produced by some germ cell tumours, and high concentrations can be detected in trophoblastic disease.
How is the sample collected for testing?
hCG is commonly measured in urine.
First-morning urine is the ideal sample.
hCG can also be measured in a blood sample taken from a vein.
How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?
How is it used?
The qualitative hCG test (reported as positive or negative) is used routinely to confirm pregnancy.
The quantitative hCG test (reported as a number), also called beta hCG, measures the concentration of hCG in the blood.
It may be requested to help diagnose an ectopic pregnancy or threatened miscarriage, or to monitor the patient after a miscarriage.
Quantitative hCG testing may also be requested to diagnose trophoblastic disease or germ cell tumours of the testicles or ovaries.
hCG concentrations may be measured periodically to monitor the effectiveness of treatment for these conditions and to detect a recurrence.
When is it requested?
The qualitative blood or urine hCG test may be requested when a period is at least ten days late, to confirm a pregnancy (some methods can measure hCG earlier, one week after conception).
In some patients several quantitative hCG tests may be requested in succession, to rule out an ectopic pregnancy or to monitor the woman after a miscarriage.
The quantitative hCG test may be requested when trophoblastic disease or germ cell tumours are suspected.
What does the test result mean?
In women who are not pregnant, hCG levels are normally undetectable.
In the first weeks of pregnancy, blood hCG levels double every two to three days.
In ectopic pregnancies hCG concentrations usually double more slowly. In a threatened miscarriage, hCG concentrations may take longer to double or may even fall.
hCG concentrations fall rapidly after a miscarriage. If hCG concentrations do not return to undetectable levels, this may indicate hCG-secreting tissue that needs to be removed.
hCG is also used to monitor the treatment of patients with trophoblastic disease and to detect a recurrence after it has been eradicated.
During treatment, falling hCG levels generally indicate that the treatment is effective, while rising levels may indicate that the tumour is not responding to treatment.
Rising hCG concentrations after treatment may indicate a recurrence.
Is there anything else I should know?
A test done too early in pregnancy, before significant amounts of hCG are produced, may give a false negative result, while blood or protein in the urine can cause false positive results. A urine hCG test can give a false negative result if the urine is very dilute. You should therefore not drink large amounts of fluid before collecting a urine sample for a pregnancy test.
Certain medicines, such as diuretics and promethazine (an antihistamine), can give false negative results for urine hCG.
Other medicines, such as anticonvulsants, anti-Parkinson medicines, hypnotics and tranquillisers, can cause false positive results.
False positive serum hCG results have been reported due to various (non-drug) substances that can interfere with the test, such as certain types of antibodies present in some people and molecular fragments of hCG.
In general, when results are doubtful, they should be confirmed with a different method.
1. How do the results of a pharmacy test compare with those of a laboratory test?
2. What is an ectopic pregnancy?
3. When is the hCG test requested on blood rather than urine?
4. How many days after a miscarriage should a urine pregnancy test be done for it to be negative?
1. How do the results of a pharmacy test compare with those of a laboratory test?
The pregnancy test bought at a pharmacy is very similar to the laboratory hCG test, but there are some points about its use that should be highlighted.
First, the pharmacy test used at home comes with detailed instructions that must be followed carefully.
Second, the pharmacy test is sometimes done in the first days after a missed period, too early to be positive. At least ten days must pass after conception before hCG can be detected in a urine sample.
This is why the pharmacy test is sometimes negative while the laboratory test is positive: the laboratory test is usually done a few days after hCG concentrations have become measurable.
All qualitative urine hCG tests should, if possible, be done on a first-morning urine sample. Urine becomes diluted after drinking fluids (coffee, fruit juice, water and so on), and urine hCG concentrations can fall too low to give a positive result.
In general, if done correctly, the pharmacy test gives a urine hCG result similar to that of the laboratory.
The qualitative blood hCG test is more sensitive than the urine test, so the blood test can sometimes be positive while the urine test is negative.
Quantitative hCG testing requires a blood sample and must be done in a laboratory.
2. What is an ectopic pregnancy?
An ectopic pregnancy is a condition in which the fertilised egg (blastocyst) implants somewhere other than the uterus. This is a serious condition that needs immediate treatment.
Patients with an ectopic pregnancy often have abdominal pain and bleeding from the uterus.
In ectopic pregnancies, hCG levels are usually unusual and rise more slowly than normal.
3. When is the hCG test requested on blood rather than urine?
The blood hCG test measures the quantitative rise in hCG, while the urine test detects the presence or absence of hCG.
Since hCG is not normally measurable in the urine of a woman who is not pregnant, a urine hCG test is enough to confirm pregnancy.
Sometimes it is important to know the hCG concentration, for example when an ectopic pregnancy is suspected, after a miscarriage or treatment, or to detect a recurring tumour.
In these circumstances a blood hCG test is requested.
4. How many days after a miscarriage should a urine pregnancy test be done for it to be negative?
Urine hCG disappears at the same rate as serum hCG, between the 9th and 35th day, with a median of 19 days.
However, the time needed for hCG to become negative depends on the hCG level at the time of the miscarriage. After a miscarriage women are often followed up by measuring blood hCG concentrations.
If hCG values do not fall to undetectable levels, hCG-secreting tissue is still present and must be removed.