The human chorionic gonadotropin test, or hCG test, is most often used to confirm pregnancy. Sometimes it is also used to diagnose certain diseases in women.
Human chorionic gonadotropin is a hormone which is produced during pregnancy. Shortly after conception this hormone is produced by the embryo, and later in the pregnancy it is produced by the placenta. The main role of this hormone is to maintain levels of the hormone progesterone, which is essential during pregnancy.
Urine hCG Tests for Pregnancy Confirmation
When a woman becomes pregnant, her hCG levels double every two to three days. Later in the pregnancy, the increase in hCG slows down somewhat, and levels double every four days.
Urine or blood levels of hCG are therefore an almost conclusive method for confirming a pregnancy. Levels of this hormone also help estimate the date on which conception occurred. However, this method of estimating the due date of the pregnancy is not entirely reliable, due to individual differences in the doubling rate of hormone levels.
Other uses of the hCG Test
There are a few other reasons why a doctor might order urine hCG tests. Levels of hCG are increased in people with germ cell tumors or trophoblastic disease, as well as ectopic pregnancy.
Germ cell tumors: these tumors usually develop in the ovaries or testes. In both women and men, abnormally high hCG levels are a feature of these tumors.
Trophoblastic disease: in this disease, embryonic cells begin to multiple abnormally. This is essentially a form of cancer, and requires treatment with chemotherapy.
Ectopic pregnancy: in an ectopic pregnancy, a fertilized egg implants into a Fallopian tube rather than the uterus. This is generally not a viable pregnancy, and can endanger the health of the pregnant woman.
Urine hCG Test Procedure
Human chorionic gonadotropin levels can be tested via blood and urine tests. in the blood test, a sample is collected from a vein, usually from the inside of the elbow.
In the urine test for hCG, a woman will urinate into a cup, or onto a prepared plastic stick. The stick method is commonly used in home pregnancy tests.
For the most accurate results, a urine sample should be taken first thing in the morning. It is best to avoid drinking large amounts of liquid before taking a urine test for hCG, as if the urine is very dilute, a false negative result might be obtained.
Interpreting the Results
The urine test for hCG can confirm a pregnancy as early as ten days after a missed period. Laboratory tests and home pregnancy tests are approximately 98% accurate. False negative tests are rare, but to ensure an accurate result, a pregnancy test should be repeated a week later.
When a woman is not pregnant, her levels of hCG are almost undetectable; therefore, detectable levels of the hormone indicate pregnancy or the possibility of disease such as trophoblastic disease.
In some cases, a single test result might not be enough to confirm a pregnancy. If there are any questions about the health of the pregnancy, several tests might be carried out. These tests are staggered over several days, so that the doubling time of hormone levels can be checked. If hCG levels fail to double in the normal amount of time, there might be a problem with the pregnancy.