The time for anti-O to fall to normal after elevation varies mainly depending on the patient’s specific situation and disease characteristics. The full name of anti-O is anti-streptococcal hemolysin O. The normal value for adults is 0-200 IU/ml. anti-O appears in the serum of patients 2 weeks after infection with group A hemolytic streptococci, peaks at about 1 month, and persists for a longer period of time. Elevation of anti-O above 500 IU/ml suggests recent streptococcal infection and is important for the diagnosis of acute tonsillitis, acute glomerulonephritis, and rheumatic fever. Since the onset of rheumatoid arthritis is associated with streptococcal infection, anti-O may be elevated in patients with the active phase of the disease and decline when they enter remission. Other diseases, such as viral hepatitis, nephrotic syndrome, and tuberculosis, can also cause elevated anti-O, but the titer is low and the anti-O will gradually return to normal as the disease gets better. Therefore, when patients have elevated anti-O, they need to be diagnosed promptly to clarify whether there are some lesions caused by streptococcal infection, and then treated according to the cause and condition.