HCG (qualitative - serum)

Alternative names:

beta-HCG - qualitative - serum; human chorionic gonadotrophin - qualitative - serum; pregnancy test - blood; qualitative serum beta-HCG; serum HCG

How the test is performed:

Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

Most pregnancy tests depend on the process of agglutination. Sensitized red blood cells are mixed with the blood (in a test tube, on a slide, or by other methods). If you are pregnant, there will be antibodies in the blood that cause the red blood cells to clump (agglutinate). Some of the more sensitive tests use monoclonal antibodies rather than sensitized red blood cells.

How to prepare for the test:

No special preparation is usually necessary.

How the test will feel:

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed:

Most often, this test is performed to confirm or rule out pregnancy. Serum HCG may also be increased in men with testicular tumors.

HCG, a hormone produced during pregnancy, is detectable in the blood or urine 1 to 2 days after implantation (10 days after ovulation). It increases rapidly in the first trimester, reaching a peak 60 to 80 days after fertilization; then drops off quickly to 10 to 30% of the peak value for the rest of the pregnancy. It serves to maintain progesterone production by the corpus luteum in the early part of pregnancy. By the time HCG drops at the beginning of the second trimester, the placenta can make sufficient progesterone to maintain the endometrium. HCG also stimulates the development of fetal gonads and synthesis of androgens by the fetal testes.