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CMV IgG Avidity

Distinguishing between recent and past cytomegalovirus (CMV) infection can be difficult in transplant recipients and pregnant women. Almost everyone with recent CMV infection have increased levels of CMV IgM. Unfortunately, some individuals with past CMV infection may also express CMV IgM following viral reactivation. Therefore, CMV IgG is not a reliable biomarker of recent infection.

Measurement of CMV IgG avidity can assist in discriminating recent from past CMV infection. A low avidity index is a reliable indicator of CMV infection within the previous 6 months while a high avidity index essentially excludes the possibility that infection occurred within the previous 4 months.

Reference range for testing performed by ELISA at Focus Diagnostics is CMV avidity index of greater than 0.6.

Specimen requirement is 0.5 mL of serum. 

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