Alternative Names qualitative pregnancy test, blood, qualitative human chorionic gonadotropin blood test, qualititative serum beta-HCG
Definition 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 is detectable in the blood and urine within 10 days of fertilisation, or conception. After the fertilised egg 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 of pregnancy and reach a peak 60 to 80 days after the fertilised egg 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:
promoting the growth of the foetus through the 12th week of pregnancy.
stimulating the development of foetal sex organs.
promoting the synthesis of male hormones by the foetal testes. Interestingly, an elevated level of HCG in men may indicate the presence of a testicular tumour.
Because HCG is produced by the placenta, the presence of HCG in a woman's blood indicates that she is most probably pregnant. HCG is produced regardless of the site of implantation of the egg in pregnancy. Usually this occurs within the uterus, but may happen outside the uterus, which is called an ectopic pregnancy. HCG in the blood may also be a sign of other conditions discussed below.
This test may be done to confirm or rule out pregnancy. Women of childbearing age who have been having sex should be screened with some type of HCG test if they are having the following symptoms:
delayed menstrual period
breast tenderness
pelvic pain
irregular spotting or bleeding
nausea or vomiting
There are two different tests to measure HCG. The other test is called a quantitative test. The quantitative test gives the exact level of HCG in the blood. This can not only determine if a woman is pregnant, but also help give a rough estimate of the age of the foetus. It can also help determine if the pregnancy is progressing normally. Levels that are abnormally low or high may be signs that an abnormal medical condition is present. This would suggest the need for further evaluation and testing.
The qualitative test is not able to provide this extra information. This test can only give a "yes" or "no" answer as to whether or not HCG is present. If the answer is "yes" the woman is most likely pregnant. This test is part of most home pregnancy test kits.
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 "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 laboratory 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 is not able to tell whether or not the pregnancy is healthy. Certain conditions besides pregnancy may cause a positive pregnancy test. These include:
a tumour of the placenta with death of the foetus
ovarian cancer and other types of cancer in some cases
blood or protein in the urine, which can interfere with the result
use of medications to prevent seizures, drugs to treat Parkinson's syndrome, or phenothiazine drugs, such as chlorpromazine, by the mother
The test may register as negative even though a woman is pregnant if the woman takes diuretic medications, or "fluid pills." These 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.
Author: Eva Martin, MD Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearne Last Updated: 6/05/2005 Contributors Potential conflict of interest information for reviewers available on request
