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Antistreptolysin O titer


Antistreptolysin O (ASO) titer is a blood test to measure antibodies against streptolysin O, a substance produced by group A Streptococcus bacteria. Antibodies are proteins our bodies produce when they detect harmful substances, such as bacteria.

Alternative Names:

ASO titer; ASLO

How the Test is Performed:

A blood sample is needed.

How to Prepare for the Test:

You should not eat for 6 hours before the test.

How the Test will Feel:


Why the Test is Performed:



Normal Results:

A negative test result means you likely have not had a recent strep infection. Your doctor may repeat the test in 2 to 4 weeks. Sometimes, a test that was negative the first time will be positive (meaning it detects ASO antibodies) when it is done again..


What Abnormal Results Mean:





  • Excessive bleeding where the needle is inserted
  • Fainting or feeling light-headed
  • Hematoma (blood buildup under the skin)




Laboratory tests and interpretation of results. In: Alvero R, Borkan JM, Ferri FF, et al, eds. Ferri's Clinical Advisor, 2014. 1st ed. Philadelphia, PA: Elsevier Mosby; 2014:section IV.

Low ED. Nonpneumoccal streptococcal infections, rheumatic fever. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 298.


Review Date: 5/11/2014


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