Anti-HCV IgG avidity index in acute hepatitis C.

Background: The diagnosis of acute hepatitis C (AHC) is based on seroconversion to positive anti-HCV, which is usually not clinically possible.

Objective: To determine if avidity of anti-HCV IgG can be used for the diagnosis of AHC infection.

Study Design: We enrolled 40 consecutive patients with AHC, 16 drug addicts (IVDA) with exacerbation of chronic hepatitis C (IVDA e-CHC group), 21 non-IVDA with exacerbation of chronic hepatitis C (IVDA-free e-CHC group) and 40 with chronic hepatitis C (CHC group). HCV avidity index (HCV-AI) was determined by ELISA on sera pre-diluted 1:10 with 1M guanidine.

Results: On admission, HCV-AI values were significantly lower in the AHC group (mean+/-S.D.: 0.50+/-0.30) than in IVDA-free e-CHC group (0.97+/-0.08, p<0.0001), IVDA e-CHC group (0.90+/-0.29, p<0.0001) or CHC group (1.06+/-0.20, p<0.0001). An HCV-AI lower than 0.7 obtained within the 8th day of illness distinguished patients with AHC infection from the IVDA-free e-CHC cases. An increase in HCV-AI was observed in 24 (72.7%) of 33 in AHC group, in none of 13 in IVDA-free e-CHC group and in 3 (27.3%) of 11 in IVDA e-CHC group.

Conclusion: HCV-AI is useful in identifying AHC infection in patients observed within the 8th day from the onset of symptoms.