Usefulness of specific IgG avidity for diagnosis of hepatitis A infection.

Aim: Diagnosis of acute hepatitis A virus (HAV) infection is classically based on the detection of HAV-IgM. Nevertheless, HAV-IgM can be positive for patients with polyclonal stimulation of their immune system (i.e. immune reactivation). To improve the diagnostic yield, an avidity test for HAV-IgG antibodies was developed and tested.
Methods: Avidity tests were performed in 128 sera: 11 selected samples from patients with past infection, 15 acute hepatitis A, 10 vaccinated subjects and 4 patients with immune reactivation as well as 84 HAV-IgM positive unselected sera, provided by routine laboratories.
Results: Patients with past infection had avidities over 70%, whereas avidities in patients with acute hepatitis A were below 50% during the first month following the onset of symptoms. As expected, patients with immune reactivation had avidities over 70% consistent with past infection. The results obtained for the 84 unselected sera allowed reconsidering the diagnosis of acute hepatitis A for nearly a third of patients.
Conclusion: This test could improve the diagnosis of acute hepatitis A infection, particularly in elderly patients.