- The test is done on the serum of patient (clotted blood 3 to 5 ml).
- A random sample can be taken.
- Avoid hemolysis.
Purpose of the test
- To diagnosis, exposure to Streptococcal infection.
- To diagnose streptococcal diseases like glomerulonephritis, rheumatic fever, bacterial endocarditis, and scarlet fever.
- Significant level was seen in glomerulonephritis and rheumatic fever.
- Avoid the drug like steroid and antibiotics.
- ASO is measured by latex agglutination or haemagglutination procedure.
- This test will measure the antibodies against Streptolysin O which is antigenic and is produced by the Group A beta-hemolytic streptococci.
- These streptococci produce streptolysin O enzyme, and this can destroy RBC (hemolysis).
- RBCs are added as indicator system.
- The ASO antibody may be found in the blood weeks or months after the infection has gone away.
- Streptolysin O is an extracellular toxin produced by many of the streptococci group, particularly by group A β-hemolyticus streptococci.
- The Streptolysin O enzyme is antigenic and immune system will produce antibody as Antistreptolysin O antibody ( ASO ).
- ASO appear in the serum after one week to one month of streptococcal infection.
- ASO has no value for the diagnosis of acute streptococcal infection.
- The serial rising titer of ASO over weeks and followed by a slow fall in titer is more significant for streptococcal infection.
- After 6 months only 30% of the patient show abnormal titer.
- Adult / elderly = < 160 Todd unit/mL or <200 IU.
- 6 months to 2 years = ≤50 Todd units/mL.
- 2 to 4 years = ≤ 160 Todd units /mL
- 5 to 12 years = 170 to 330 Todd units/mL.
- If it is above 200 then it is a significant level.
- Greater than 500 Todd unite indicate Acute rheumatic fever or acute post-streptococcal glomerulonephritis.
- Serial assay of ASO should be advised for rising titer.
ASO is positive in:
- Acute streptococcal infections.
- Bacterial Endocarditis.
- Post-streptococcal glomerulonephritis ( 50 to 70 % of the patients shows no high titer ).
- Rheumatic fever
- Scarlet fever
- ASO is often not raised in these diseases.
- An increased titer may be found in the healthy carrier.
- Antibiotic therapy may suppress the antibody response.
- Increased Lipoprotein level inhibit Streptolysin O and produce false high ASO titer.
Possible References Used
Back to tests