| Definition: |
A blood test to detect the presence of antibodies against a microorganism.
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| How the test is performed: |
Adult or child:
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.
Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
The blood is then analyzed in a laboratory. Serology refers to the study of serum for its antibody content. Certain microorganisms (antigens) stimulate the body to produce these antibodies during an active infection. In the laboratory, the antibodies react with antigens in specific ways that can be used to confirm the identity of the specific microorganism. There are several serology techniques that can be used depending on the suspected antibodies. Serology techniques include agglutination, precipitation, complement-fixation, fluorescent antibodies, and others. |
| How to prepare for the test: |
Adults:
There is no special preparation.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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| 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: |
| A serology may be performed when an infection is suspected. |
| Normal Values: |
| No antibodies are detected. However, during the first few days to weeks of exposure to an antigen, there may be slight antibody production. As the disease progresses, more antibodies will be present. If a disease is suspected, the test may need to be repeated 10 days to 2 weeks after the first test. |
| What abnormal results mean: |
| If antibodies are detected, there has been exposure to an antigen. Some of the different diseases that can be detected include:Additional conditions under which the test may be performed:
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| What the risks are: |
- excessive bleeding
- fainting or feeling lightheaded
- hematoma (blood accumulating under the skin)
- infection (a slight risk any time the skin is broken)
- multiple punctures to locate veins
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| Special considerations: |
A serology test can determine if a patient has ever been exposed to a particular microorganism (antigen), but this does not necessarily indicate a current infection.
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others. |
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Review Date: 2/17/2002
Reviewed By: Michael C. Milone, M.D., Ph.D., Department of Pathology and Laboratory Medicine, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
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