How is the serum titer in the antistreptolysin O (ASO) test reported?

The antistreptolysin O (ASO) test is utilized to measure the level of antibodies against streptolysin O, a toxin produced by Group A Streptococcus bacteria. When interpreting the results of this test, the serum titer is most conventionally reported in Todd or International Units.

Todd units represent a standardized measurement that reflects the highest dilution of serum that still shows a positive reaction, indicating a higher concentration of antistreptolysin O antibodies. International Units serve as a global standard for measuring various biological substances, including antibodies, allowing for consistency across different clinical laboratories and research studies. This standardized reporting is crucial for assessing the significance of the antibody levels in the context of potential streptococcal infections or sequelae, such as rheumatic fever.

The other response options do not pertain to the standardized method for reporting ASO titers. Using milliliters per liter, percentage of total volume, or grams per deciliter does not apply to this immunological assessment. The use of Todd or International Units ensures clarity and uniformity in understanding and interpreting results in clinical practice.