Interpreting serology reports in dengue infection

Abstract

Dengue infection is diagnosed by the clinical picture and confirmed by laboratory evidence of dengue non-structural protein 1 (NS1) antigen (first 5 days) or dengue immunoglobulin M (IgM) antibody (beyond the 5th day). However, in secondary dengue infection, the IgM antibody levels do not rise much and the diagnosis may be missed if the levels if IgG antibodies are not considered. A 5-year-old child presented with fever, cough, and vomiting for 4 days. A diagnosis of respiratory infection was made and she was treated accordingly. She developed abdominal pain on day 3 of admission and ultrasound abdomen showed ascites and pleural effusion. Dengue fever with plasma leak was suspected. Since it was day 6 of illness, dengue serology was sent. The dengue IgM antibodies were low (5.4 IgM units [Positive >11 IgM units]).However, dengue immunoglobulin G (IgG) antibody level was 13.34 units and the IgG/IgM ratio was 2.4. A diagnosis of secondary dengue was made. The child improved with supportive measures and was subsequently discharged. To conclude, awareness about the phases of dengue fever and correct interpretation of serological tests is needed for diagnosis and appropriate management.