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IgG Avidity

Published: July 27, 2026Updated: August 25, 2026

IgG avidity measures the strength of binding between IgG antibodies and their specific antigens, which helps distinguish between recent and past infections.

Quick summary

IgG avidity differentiates recent from past infections by measuring antibody-antigen binding strength.

Medically reviewed by WellAlly Editorial TeamLast reviewed August 25, 2026Editorial policy

Key facts at a glance

Units
index
Clinical utility
diagnostic
Result kind
qualitative
FDA-cleared
Roche Avidity, Abbott Avidity
interpretation: {"text":"Suggests a recent infection, typically within the past 4-6 months.","label":"Low Avidity (0–0.3)"}; {"text":"Indicates a past infection, likely occurring more than 6 months ago.","label":"High Avidity (>0.6)"}

IgG avidity testing is a valuable diagnostic tool used to determine the maturity of an immune response. By assessing the strength of the bond between IgG antibodies and their target antigens, clinicians can infer whether an infection is recent or occurred in the past.

A low IgG avidity index typically indicates a recent infection, as the antibodies are still in the process of maturing and have a weaker binding affinity. Conversely, a high avidity index suggests that the infection happened in the past, as the antibodies have had time to strengthen their bonds.

This biomarker is particularly useful in cases where the timing of infection is critical, such as in prenatal screenings for infections like toxoplasmosis and cytomegalovirus, which can have severe consequences for fetal development.

Frequently asked questions

What is the normal range for IgG avidity?
The normal range for IgG avidity is typically considered to be between 0 and 1, with values below 0.3 indicating recent infection and values above 0.6 indicating past infection.
Can IgG avidity testing be used for all infections?
IgG avidity testing is most commonly used for infections like toxoplasmosis, cytomegalovirus, and rubella, where distinguishing between recent and past infections is important.
  1. 1
    IgG Avidity Testing in the Diagnosis of Infectious DiseasesSource
  2. 2
    Clinical Utility of IgG Avidity TestingSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 25, 2026. · Read our editorial policy