Method variation of cytomegalovirus IGM assays in EQA

Abstract

Cytomegalovirus (CMV) is a common virus that infects people of all ages. Correctly diagnosing a primary CMV infection in pregnant women is critical to avoid congenital anomalies. CMV IgM specificity is poor in detecting primary infections due to vial reactivation or persistence following primary infection. Algorithms using CMV IgM and IgG avidity can be useful. We sought to review the performance of CMV IgM and IgG avidity assays in the RCPAQAP CMV External Quality Assurance (EQA) Program. Data sourced from an expected IgM positive consenting donor sample was assessed using RCPAQAP software. The same sample was included in four surveys over three years. Variation in the quantitative IgM data across methods was consistently noted (e.g., Roche vs Diasorin). There were also similar differences in the qualitative interpretations between the ‘negative’ and ‘positive’ groups (21 vs 92, respectively). While 120 sites reported for IgM, only 34 of these measured IgG avidity which more than 95% reported as ‘high’. In a clinical setting, access to both results may be of benefit. While the study was limited, further investigation of discrepancies between CMV methods when interpreting results should be considered. The inclusion of IgG avidity is recommended.