Serum Pregnancy Test, Qualitative
- qualitative pregnancy test, blood
- qualitative human chorionic gonadotropin blood test
- qualititative serum beta-HCG
This is a test that detects the presence of the pregnancy hormone, human chorionic gonadotropin (HCG), in the bloodstream.
Who is a candidate for the test?
HCG is a hormone that is produced by the placenta. It appears in the blood and urine within 10 days of fertilization of the egg by the sperm (conception).
After the unborn child begins developing, he or she implants, or attaches, to the inside of the uterus or other structure inside the mother, the levels of HCG rise rapidly. The levels continue to increase throughout the first trimester (3 months) of pregnancy and reach a peak 60 to 80 days after the unborn child implants.
HCG is thought to be important in converting the normal corpus luteum into the corpus luteum of pregnancy. The corpus luteum is a hormone-secreting structure that grows on the surface of the ovary after ovulation takes place.
In pregnancy, functions of the corpus luteum include:
Because HCG is produced by the placenta, the presence of HCG in a woman's blood almost always indicates that she is pregnant. HCG is produced whether the unborn child implants in the uterus (the normal situation) or outside the uterus in the fallopian tube or on another structure in the abdomen or pelvis (an ectopic pregnancy).
An HCG test is usually done to confirm or rule out pregnancy. Women of childbearing age who have been having sex should be evaluated with some type of HCG test if they are having the following symptoms:
There are two different tests to measure HCG:
One, called a quantitative test, measures the exact level of HCG in the blood. The result can not only determine if a woman is pregnant, but also help give a rough estimate of the duration of the pregnancy. It can also help determine if the pregnancy is progressing normally. Levels that are abnormally low or high suggest the need for further evaluation and testing to determine whether an abnormal medical condition is present.
The qualitative test is not able to provide this extra information. Rather, it gives only a "yes" or "no" answer as to whether or not HCG is present. If the answer is "yes" the woman is most likely pregnant.
A version of this test can also be performed on a urine sample; however, the urine test is less sensitive and therefore does not turn positive until the pregnancy is a few weeks farther along.
How is the test performed?
A blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a strong rubber tube, or "tourniquet," is wrapped around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them.
A fine needle is gently inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle, and is collected in a syringe or vial. After the needle is withdrawn, the puncture site is covered with a bandage for a short time to prevent bleeding. The blood is sent to the lab to determine the whether or not HCG is present in the blood. When HCG is present, the test is called positive and a woman is most likely pregnant.
What is involved in preparation for the test?
No special preparation is necessary for this test.
What do the test results mean?
Because the placenta produces HCG, it is an indicator of pregnancy. This test cannot distinguish whether or not the pregnancy is healthy.
Certain conditions besides pregnancy may cause a positive pregnancy test. These include:
If the woman is taking diuretic medications, or "water pills", the HCG test may register as negative even though she is pregnant, because the drugs interfere with the test results. In addition, the test does not become positive until at least 7 to 10 days after a woman becomes pregnant. In most cases, by the time a woman misses her period the test will be positive if she is pregnant.