Antistreptolysin O is an antibody produced by Group A streptococci (GAS). Levels rise 1 – 4 weeks after an infection, peak between week 3 and 5 and may remain detectable for a few weeks after an infection. >200 is abnormal in adults, opinions differ in the literature as to whether children should have the same cut off but most clinicians use this number for everyone.

ASOT does not predict which people will get complications of GAS eg. rheumatic fever, glomerulonephritis. Click here to comment and join the discussion on when ASOT should be measured and what to do with the result