| Subject | Contents |
| Definition | A blood test to measure anti-streptolysin O (ASO) antibodies in the blood. |
| Alternative Names | Anti-streptolysin O titer |
| 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 sent to the laboratory for analysis. |
| How to prepare for the test | Fast for 6 hours before the test. Interfering factors such as high levels of beta lipoproteins can affect the test results. 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 experiences, 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:infant test or procedure preparation (birth to 1 year) toddler test or procedure preparation (1 to 3 years) preschooler test or procedure preparation (3 to 6 years) schoolage test or procedure preparation (6 to 12 years) adolescent test or procedure preparation (12 to 18 years) |
| 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 | The test is used to detect prior infection by Group A Streptococcus. This bacterium is responsible for diseases such as glomerulonephritis , rheumatic fever , bacterial endocarditis , and scarlet fever . ASO testing is a procedure that demonstrates the presence of antibodies generated by the body against the enzyme streptolysin O, which is produced by the bacteria and which causes destruction of red blood cells (hemolysis). The ASO antibody may be detected in the blood for weeks or months after the primary source of the infection has been eradicated.
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| Normal Values | The ASO level is usually less than 160 Todd units per milliliter. |
| What abnormal results mean | Elevated levels may indicate:active streptococcal infectionbacterial endocarditispost-streptococcal glomerulonephritisrheumatic feverscarlet fever |
| What the risks are | excessive bleedingfainting or feeling light-headed hematoma (blood accumulating under the skin) infection (a slight risk any time the skin is broken) multiple punctures to locate veins |
| Special considerations | 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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