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Antistreptolysin-O (ASLO) Unit Converter
Antistreptolysin-O (ASLO or ASO) is an antibody produced by the host immune system in response to Streptolysin O, a toxic enzyme secreted by Group A Streptococcus (GAS) bacteria (Streptococcus pyogenes). Streptolysin O is responsible for the hemolysis (red blood cell rupture) seen in streptococcal infections.[Image of streptococcus pyogenes structure]
The ASLO titer is the most widely used serological test to confirm a recent streptococcal infection, such as strep throat or scarlet fever. It is critically important in the diagnosis of non-suppurative post-streptococcal sequelae, particularly Rheumatic Fever and Post-Streptococcal Glomerulonephritis. While the historical “Todd Unit” was the original standard, modern laboratories report results in International Units (IU/mL or kIU/L). This converter allows seamless switching between these equivalent standards.
SI Units
RecommendedKilo-International Units per liter (Numerically = IU/mL).
Conventional Units
Clinical Context
ASLO antibodies appear in the serum approximately 1 week after infection, peak around 3–5 weeks, and can remain elevated for months. A single elevated titer is less specific than a rising titer (measured 2 weeks apart).
Reference ranges vary by age and geography (due to prevalence of strep). In adults, values < 200 IU/mL are generally considered normal. In school-aged children, the upper limit is often higher (< 400 IU/mL). Note: 20% of patients with proven strep infection may not show elevated ASLO; in such cases, Anti-DNase B is usually tested.
Clinical References
How to Use This Calculator
Follow these steps to get accurate clinical conversions instantly.
Enter Values
Input your laboratory results into the corresponding unit field (e.g., IU/mL). You can use either dot or comma decimals.
Automatic Conversion
The calculator works in real-time. As you type in one field, all other units (like Todd Units) are instantly updated.
Verify Units
Check the SI Units section. kIU/L is numerically identical to the common IU/mL.
Reset
Use the Clear button to reset all fields before starting a new calculation.
Frequently Asked Questions & Tips
The original unit defined by E.W. Todd in 1932 based on hemolysis inhibition. 1 Todd Unit is considered equivalent to 1 International Unit (IU).
ASLO measures the functional ability of antibodies to neutralize toxin, not their physical weight.