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Multicenter evaluation of a rapid and convenient method for determination of cytomegalovirus immunoglobulin G avidity
M Baccard-Longere1, F Freymuth, D Cointe
1Laboratoire de Virologie, Centre Hospitalier Universitaire de Grenoble, BP 217, 38043 Grenoble, France. MBaccard@chu-grenoble.fr
Insights
A new VIDAS CMV IgG avidity test can quickly differentiate recent cytomegalovirus (CMV) primary infections from past infections. This rapid test is especially valuable for pregnant women, improving diagnostic accuracy for CMV status.
Area of Science:
- Virology
- Immunology
- Clinical Diagnostics
Background:
- Distinguishing primary cytomegalovirus (CMV) infections from past infections or reactivations is crucial, particularly in pregnant women.
- Residual immunoglobulin M (IgM) antibodies can complicate diagnosis, necessitating reliable methods for assessing recent CMV infection.
- Assessing the avidity of immunoglobulin G (IgG) antibodies offers a potential solution for differentiating infection timelines.
Purpose of the Study:
- To evaluate the VIDAS CMV IgG avidity test for differentiating primary CMV infections from past infections or reactivations.
- To determine the effectiveness of CMV IgG avidity testing using the VIDAS assay and 6 M urea in a multicenter study.
- To establish reliable avidity index cutoffs for diagnosing recent primary CMV infections.
Main Methods:
- A multicenter study involving 416 serum specimens: 159 from primary infections and 257 from past infections.
- Utilized the VIDAS automated enzyme-linked fluorescent assay with 6 M urea to measure CMV IgG antibody avidity.
- Analyzed avidity index values in relation to the time elapsed since the onset of primary CMV infection.
Main Results:
- An avidity index below 0.8 effectively excluded primary CMV infections within the last 4 months (17 weeks).
- An avidity index below 0.2 strongly confirmed a recent primary CMV infection (less than 4 months).
- While a cutoff of 0.7 improved exclusion rates to 96.9%, it reduced specificity, as some recent infections showed avidity between 0.7 and 0.8.
Conclusions:
- The VIDAS CMV IgG avidity test is a rapid, reproducible, and high-performing assay.
- An avidity index below 0.2 is a reliable indicator of recent primary CMV infection (<4 months).
- The test aids in differentiating recent primary CMV infections from past infections or reactivations, with significant clinical utility, especially for pregnant women.
Abstract:
An easy, rapid, and reproducible test to distinguish residual cytomegalovirus (CMV) immunoglobulin M (IgM) antibodies from antibodies produced in primary infection could be useful, especially for pregnant women. The CMV avidity of IgG antibodies with the VIDAS automated enzyme-linked fluorescent assay and 6 M urea was evaluated in a multicenter study to differentiate between primary CMV infections and past infections or reactivations. A total of 416 serum specimens were tested: 159 specimens were from follow-up of primary infections, and 257 were from past infections. All of the specimens from primary infections collected within 4 months (17 weeks) after the onset of the infection had an avidity index lower than 0.8. An avidity index higher than 0.8 excludes a recent primary infection of less than 4 months. However, an avidity index higher than 0.8 cannot confirm all past infections, since 48 specimens (18%) from past infections had an avidity index lower than 0.8 (between 0.5 and 0.8). The exclusion capacity could be improved (96.9%) by using a cutoff of 0.7, but this index would decrease the specificity of the technique, since the avidity index was found to be between 0.7 and 0.8 in two patients with recent primary infection. All specimens from primary infections obtained more than 4 months after the onset of infection had an avidity index more than 0.2. In this study, an avidity index less than 0.2 confirms the presence of a recent primary infection of less than 4 months. The VIDAS CMV IgG avidity test is a rapid, reproducible test with very good performance.
