Clinical utility of avidity assays

Area of Science:

• Immunology
• Infectious Diseases
• Medical Diagnostics

Background:

• Immunoglobulin M (IgM) can persist for extended periods, potentially causing diagnostic errors when serology is the sole diagnostic method.
• Nonspecific immune stimulation and cross-reactivity can lead to the detection of IgM during secondary infections.
• Distinguishing between primary and past infections is critical for accurate diagnosis and patient management, especially in vulnerable populations.

Purpose of the Study:

• To evaluate the utility of IgG avidity testing in differentiating acute from past infections.
• To assess the role of IgG avidity testing in managing specific infectious diseases like congenital toxoplasmosis, cytomegalovirus (CMV), and West Nile virus (WNV).
• To highlight the limitations of relying solely on IgM detection for diagnosing acute infections.

Main Methods:

• Review and analysis of the principles and applications of IgG avidity testing in serological diagnosis.
• Examination of clinical scenarios where IgM persistence complicates diagnosis, including toxoplasmosis, CMV, and WNV infections.
• Comparison of diagnostic accuracy between IgM detection alone and combined IgM/IgG avidity testing.

Main Results:

• IgG avidity increases over time following infection, providing a marker to distinguish recent from past infections.
• IgG avidity testing aids in assessing fetal risk in congenital toxoplasmosis and differentiating primary from secondary CMV infections in pregnant women.
• In WNV infections, IgG avidity testing can help clarify positive IgM results that may represent past exposure.

Conclusions:

• IgG avidity testing is a valuable adjunct to serological diagnostics, improving the accuracy of infection timing assessment.
• The persistence of IgM necessitates complementary testing, such as IgG avidity, for reliable diagnosis of acute infections.
• While a powerful tool, IgG avidity testing should be interpreted within the broader clinical context and with an understanding of its limitations.