Cytomegalovirus (CMV) IgG Avidity Testing ... - Focus Diagnostics

T E C H N I C A L S U M M A R YFocus Diagnostics Reference Laboratory ServicesSummary:Approximately 50% ofpregnant women withprimary CMV infectiontransmit CMV to theirinfants. Measuring CMVIgG avidity can reliablydistinguish primaryinfection from nonprimaryinfection duringpregnancy.To send specimensor obtainadditional information,please contact ourClient ServicesDepartmentat 800-445-4032.For technical assistance,contactFocus Diagnostics’Scientific Directorof Immunology.ISO 13485:2003 CertifiedQUALITY MANAGEMENT SYSTEMCytomegalovirus (CMV) IgG Avidity TestingA Tool for Identifying Primary CMV InfectionCytomegalovirus (CMV), an ubiquitous memberof the herpes virus family, is responsible for arange of infections in humans of all ages. Amongthe most clinically important forms of CMV diseaseis congenital infection. Intrauterine CMV infectionoccurs in approximately 1% of all live births, withup to 15% of congenitally infected infants showingsymptoms at birth. These symptoms include anycombination of microcephaly, intracranialcalcifications, chorioretinitis, jaundice,hepatosplenomegaly, and purpura.The mortality rate among symptomatic infants canbe as high as 30%; the symptomatic infants whosurvive are likely to develop long-term neurologicsequelae, including hearing loss, visualimpairment, psychomotor delay, and mentalretardation. Intrauterine CMV infection is secondonly to Down’s syndrome as a cause of mentalretardation. Of the 85% of congenitally infectedinfants who are asymptomatic at birth,approximately 15% develop neurologic sequelaeby 4 years of age.The debilitating effects of congenital CMV infectionare strongly linked to maternal primary infection,rather than reinfection or reactivation, duringpregnancy. Approx-imately 50% of women withprimary CMV infection during pregnancy transmitCMV to their infants, compared to only 0.5% ofwomen with CMV re-infection or reactivation.Further, among those few infants who becomeinfected following maternal reinfection orreactivation, symptoms and debilitating sequelaeare extremely rare. Thus, the challenge to thephysician caring for a pregnant woman withclinical or serologic evidence of CMV infection is todetermine if the infection represents a newlyacquired (primary) infection, or represents eitherre-infection or reactivation of a pre-existing(nonprimary) infection.Serological Response to InfectionSince >90% of CMV infections inimmunocompetent adults (including pregnantwomen) are asymptomatic, detection of CMVspecificantibodies is the most common approachused to identify CMV infection. CMV-specific IgMis an extremely sensitive marker of primary CMVinfection; unfortunately, CMV IgM detection is notspecific for primary infection, due to its productionfollowing re-infection or reactivation in someindividuals. Likewise, demonstration of increasinglevels of CMV-specific IgG over time is animpractical approach for distinguishing primaryfrom non-primary CMV infection, since mostpatients already show high IgG levels in the firstserum sample collected for testing.Antibody AvidityMeasurement of CMV-specific IgG avidity hasproven to be a powerful tool for distinguishingprimary from non-primary CMV infection. Definedas the strength with which the IgG attaches toantigen, IgG avidity matures with the length of timefollowing primary infection. Thus, IgG producedwithin the first few months following primaryinfection exhibits low avidity, whereas IgGproduced several months or years later exhibitshigh avidity. Several groups of investigators haveshown that detection of CMV specific IgG of lowavidity is a reliable indicator of infection within theprevious 6 to 8 months. However, detection ofCMV-specific IgG of high avidity is actually moreinformative from a clinical standpoint; thepresence of high avidity IgG essentially excludesthe possibility that infection occurred within theprevious 4 months.Case Study — Practical ApplicationTo demonstrate the power of CMV IgG aviditymeasurement, consider the case of a pregnantwoman making her first prenatal care visitapproximately 10 weeks after conception; serumcollected during this visit contained CMV-specificIgG and IgM. The positive IgM result may indicateprimary infection during the time period sinceconception. Alternatively, it may merely indicateeither re-infection or reactivation of latent CMVinfection, thus signaling that primary CMVinfection occurred several months or years earlier,prior to conception. If the first possibility is true,congenital infection of the fetus is a concern, andinvasive procedures to further assess possibleCMV-induced fetal damage may be necessary; ifthe second possibility is true, however, the fetus ismost likely protected against debilitating CMVinfection.A CMV-specific IgG avidity assay will helpdistinguish between these two possibilities. Whenthis test is performed on the same serum samplefound to be IgG-positive and IgM-positive, a highavidity result is obtained.This information indicatesthat primary infection occurred well beforeconception, and the chance of debilitatingcongenital CMV infection is very low. Results willvary with each patient.continued on following page

Cytomegalovirus (CMV) IgG Avidity TestingDescription of MethodFocus Diagnostics’ CMV IgG avidity ELISA utilizes urea, an agentthat disrupts hydrogen bonds, to differentiate low avidity from highavidity antibodies. Following attachment to immobilized antigen,low avidity IgG readily dissociates from the antigen in the presenceof urea, whereas high avidity IgG does not. Thus, avidity isassessed by performing duplicate sets of the routine enzymelinkedimmunosorbent assay (ELISA) for CMV-specific IgG; theonly difference is that, after the initial incubation, one set is washedwith buffer containing urea, and the other set is washed with bufferlacking urea.The CMV-specific IgG signal (optical density) of the set washedwith urea buffer is then divided by the CMV-specific IgG signal ofthe set washed with non-urea buffer, thus providing the avidityindex (AI). AI values ≤ 0.50 indicate low avidity, values of 0.51-0.59indicate intermediate avidity, and values ≥ 0.60 indicate highavidity.Focus Diagnostics evaluated their CMV IgG avidity ELISA usingtwo panels of well characterized sera. The first panel included CMVIgG positive sera from pregnant women who had recentlyseroconverted following primary CMV infectionThe first panel included CMV IgG positive sera from pregnantwomen who had recently seroconverted following primaryCMV infection. All sera were collected in the 4-month periodfollowing the last IgG negative sample. The second panelincluded sera from patients with past CMV infection, as shownby a CMV IgG positive/ IgM negative profile.The resultsshowed that 99% of sera from patients with primary CMVinfection exhibited low avidity, whereas 98% of sera frompatients with past CMV infection exhibited high avidity.SummaryIn summary, assessment of CMV-specific IgG avidity is apowerful tool for estimating the time of CMV infection. Suchinformation is particularly important in the clinical managementof pregnant women found to be positive for CMV antibodies attheir first prenatal visit. Determining the time of primaryinfection can help guide decisions regarding antiviral therapyby identifying those women who should or should not betreated during pregnancy. CMV IgG avidity measurement alsohas broad applicability to the management of other patientgroups with an increased risk of debilitating CMV disease,such as solid organ transplant recipients.For complete specimen information and CPT codes view ourReference Laboratory test listing on our Web site at www.focusdx.comCode #Test Description42600 Cytomegalovirus (CMV) IgG Avidity ELISA2426 Cytomegalovirus (CMV) Recent Infection Antibody PanelPanel includes:Cytomegalovirus (CMV) IgG Antibody, ELISACytomegalovirus (CMV) IgM Antibody, ELISACytomegalovirus (CMV) IgG Avidity ELISAREFERENCES:• Baccard-Longere M et al. Multicenter evaluation of a rapid and convenient method for determination of cytomegalovirus immunoglobulin G avidity. Clin Diagn LabImmunol 8:429-431,2001• Bodeus M et al. Avidity of IgG antibodies distinguishes primary from non-primary cytomegalovirus infection in pregnant women. Clin Diagn Virol 9:9-16,1998• Bodeus M, Goubau P. Predictive value of maternal-IgG avidity for congenital human cytomegalovirus infection. J Clin Virol 12:3-8,1999• Bodeus M et al. Ability of three IgG-avidity assays to exclude recent cytomegalovirus infection. Eur J Clin Microbiol Infect Dis 20:248-252,2001• Eggers M et al. Combination of microneutralization and avidity assays: improved diagnosis of recent primary human cytomegalovirus infection in single serum sampleof second trimester pregnancy. J Med Virol 60:324-330,2000• Fowler SL. A light in the darkness: predicting outcomes for congenital cytomegalovirus infections. J Pediatr 137:4-6,2000• Gangeot-Keros L et al. Value of cytomegalovirus (CMV) IgG avidity index for the diagnosis of primary CMV infection in pregnant women. J Infect Dis 175:944-946,1997• Lazzarotto T et al. Avidity of immunoglobulin G directed against human cytomegalovirus during primary and secondary infections in immunocompetent andimmunocompromised subjects. Clin Diagn Lab Immunol 4:469-473,1997• Lazzarotto T et al. Anticytomegalovirus (anti-CMV) immunoglobulin G avidity in identification of pregnant women at risk of transmitting congenital CMV infection. ClinDiagn Lab Immunol 6:127-129,1999• Lazzarotto T et al. Maternal IgG avidity and IgM detected by blot as diagnostic tools to identify pregnant women at risk of transmitting cytomegalovirus. Viral Immunol13:137-141,2000• Lazzarotto T et al. Prenatal indicators of congenital cytomegalovirus infection. J Pediatr 137:90-95,2000• Lazzarotto T et al. New advances in the diagnosis of congenital cytomegalovirus infection. J Clin Virol 41: 192-197, 2008.To send specimens or obtain additional information, please contact our Client Services Department at 800 445 4032.For technical assistance, contact Focus Diagnostics’ Scientific Director of Immunology.800-445-0185 • 714-220-1900 • Fax: 714-220-9213Cypress, California 90630 USAwww.focusdx.comRLCMV0509