Categories: Arthritis tests

ASO Titer Explained

Previously we presented what is ASO titer meaning, and what to do when ASO titer go positive in blood results, this is to list the normal ASO titer and abnormal ASO titres that require more investigations, medical action and treatment.

Previous Elevated ASOT meaning


ASO is a medical term for “antistreptolysin O”, antistreptolysin O is a medical term for “ASO antibody” or “ASO Ab”, which is a weapon released against foreign attacks by a substance called “streptolysin O”, streptolysin O is a bacterial toxin breaks blood cells and causes hydrolysis of your blood, complications of high ASO titers include kidney inflammation, arthritis, rheumatic fever which scars the valves of the heart.

Strep‘ is a shortcut for Streptococcus bacteria

Titer or titre means “concentration” or “unit”

Normal ASO titer range  is 100 IU/mL for adult and preschool age child, 200 IU/mL for child at school age

It’s better to call it negative level than normal level.

ASO test is a measure of the antistreptolysin O antibodies level in your blood,

When ASOT blood test results show:

A value from 0.0 to 250 unit/ml it means probably no strep infection, ASO titer from 250 to 400 titer/ml means equivocal result need a confirmation by serial testing, ASO titer higher than 400 titer/ml means probable recent strep infection.

ASO test are used when searching for evidence of recent streptococcal infection in suspected post-streptococcal glomerulonephritis (PSGN) ” a kidney inflammation disease” or rheumatic fever (RF).
Serial ASOT tests should be done, looking for rising titers.

A high ASO level is more likely to be significant and sustained ASO levels may indicate persisting infection. PSGN or RF can easily be over-diagnosed when an isolated, equivocal, titre is used as evidence.

See more ASOT results interpretation:

7 years daughter had ASO titre over 1000 and knee pain

ASOT Titre 800 and CRP 30

Confirmation Tests after High ASO Titer:

Time-course after streptococcal infection ASOT and ASK start to rise a few days after infection commences. ADNAse tends to rise somewhat later. In uncomplicated infections, ASOT does not usually rise in streptococcal skin infections whereas ADNAse does.

How long time does ASO titer take to be normal again?

ASO titres return to baseline levels in 23 months. Average ASO baseline levels in adults are half those in children due to the frequent streptococcal throat infections in the latter.


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