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PubMed This is a summary of 19 peer-reviewed journal articles Updated
Infectious Disease

Pathology & Testing: Understanding Your CMV Lab Reports

At a Glance

A CMV lab report uses serology (IgG and IgM) to detect antibodies and PCR tests to measure actual viral DNA. IgG avidity helps date the infection, which is crucial during pregnancy, while quantitative PCR monitors viral loads to guide treatment in transplant and HIV patients.

Laboratory reports for Cytomegalovirus (CMV) can be confusing because the “correct” interpretation depends entirely on your health situation—whether you are pregnant, a transplant recipient, or the parent of a newborn. A “positive” result might be a normal finding for one person but a sign that requires immediate action for another.

Decoding Serology: IgG, IgM, and Avidity

Serology tests look for antibodies, which are proteins your immune system makes in response to the virus.

  • CMV IgG (The “Memory” Antibody): A positive result means you have been exposed to CMV at some point in your life [1]. If your IgG was negative last month but is positive now, it confirms a primary (new) infection.
  • CMV IgM (The “Early” Antibody): A positive result often suggests a recent infection [2]. However, IgM is notoriously “sticky” and can lead to false positives if you have other infections like mono (EBV) or even COVID-19 [3][4]. It can also stay positive for many months after an old infection.
  • IgG Avidity (The “Timer”): This is the tie-breaker test. It measures how “strong” the bond is between the virus and your IgG antibodies.
    • Low Avidity: Suggests a new infection (usually within the last 3 months) [5].
    • High Avidity: Suggests an old infection (at least 3 to 6 months ago), which is often a reassuring sign in pregnancy [6].

Understanding PCR: Viral Load

Unlike serology, PCR (Polymerase Chain Reaction) tests look for the actual DNA of the virus.

  • Quantitative PCR (Transplant & HIV): This report gives you a number in IU/mL (International Units per milliliter). Doctors use this to monitor “viremia” (virus in the blood). A rising number may trigger preemptive therapy to stop the virus before it causes symptoms [7][8].
  • Qualitative PCR (Newborns): This is usually a “Detected” or “Not Detected” result.
    • Saliva PCR: Used for screening newborns. However, because CMV can be in breast milk, a positive saliva test must be confirmed with a urine PCR to make sure the baby was actually infected in the womb [9][10].
  • Amniotic Fluid PCR: Used during pregnancy (amniocentesis) to see if the virus has passed to the baby [11].

Laboratory “Completeness Checklist”

Empower yourself by ensuring your medical team has performed the necessary tests for your situation.

For Pregnant Patients

  1. Baseline IgG/IgM: To establish your current status.
  2. IgG Avidity: Required if IgM is positive to determine the infection’s age [1].
  3. Serial PCR: (If applicable) To monitor viral levels if treatment like valacyclovir is started.

For Transplant Recipients

  1. D/R Status: Knowing if the donor (D) and recipient ® were positive (+) or negative (-) before surgery [12].
  2. Weekly Quantitative PCR: Standard for the first 12 weeks for those not on preventive medicine [13].
  3. Basic Metabolic Panel (BMP): To monitor kidney function (creatinine) if you are taking antiviral medications [14].

For Newborns

  1. Saliva PCR: Performed within the first 21 days [15].
  2. Urine PCR Confirmation: If the saliva test was positive [9].
  3. Absolute Neutrophil Count (ANC): To check white blood cell levels if the baby starts treatment [16].

For HIV/AIDS Patients

  1. CD4 Count: To determine if you have crossed the critical threshold (< 50 cells/μL) where CMV can cause damage [17].
  2. CMV PCR: To monitor the level of virus in your blood if symptoms arise [18].
  3. Dilated Fundus Exam: Essential for detecting CMV retinitis early if your CD4 count is critically low [19].

Common questions in this guide

What does a positive CMV IgG test mean?
A positive CMV IgG result indicates that you have been exposed to the cytomegalovirus at some point in your life. If your test was recently negative and is now positive, it confirms a brand new infection.
Why is an IgG avidity test important for CMV?
The IgG avidity test helps determine how recently you were infected with CMV. A low avidity score suggests a new infection within the last three months, while a high avidity score indicates an older infection, which is often reassuring during pregnancy.
Can a CMV IgM test have a false positive?
Yes, CMV IgM tests can be falsely positive if you have or recently had other infections like mononucleosis (EBV) or COVID-19. The IgM antibody can also remain positive for many months after an old infection has resolved.
What does a quantitative PCR test measure for CMV?
A quantitative PCR test measures your viral load, meaning the actual amount of CMV DNA in your blood. Doctors use this number to monitor the virus and decide if antiviral treatment is needed before symptoms develop.
How is a newborn tested for CMV?
Newborns are initially screened with a saliva PCR test within their first 21 days. Because breast milk can contain CMV and cause a false positive, a positive saliva test must always be confirmed with a urine PCR test.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What is my current serostatus (D/R status), and how does that affect my risk level?
  2. 2.Since my IgM test was positive, can we order an IgG avidity test to help determine when I was first infected?
  3. 3.What is the specific numerical value (IU/mL) of my PCR viral load, and how does that compare to the threshold for starting treatment?
  4. 4.If my baby's saliva PCR was positive, have we scheduled a follow-up urine PCR to confirm it wasn't just a false positive from breast milk?
  5. 5.Are my blood counts (white cells and platelets) being monitored alongside my CMV viral load?

Questions For You

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References

References (19)
  1. 1

    Cytomegalovirus infection in pregnancy - An update.

    Navti OB, Al-Belushi M, Konje JC,

    European journal of obstetrics, gynecology, and reproductive biology 2021; (258()):216-222 doi:10.1016/j.ejogrb.2020.12.006.

    PMID: 33454510
  2. 2

    Deciphering Positive Cytomegalovirus Immunoglobulin M Test Results in Immunocompetent Adults Hospitalized With Illness Suspicious for Acute Cytomegalovirus Infection: A Multihospital Study.

    Samuel S, Thomas S, Asleson L, et al.

    Open forum infectious diseases 2025; (12(3)):ofaf144 doi:10.1093/ofid/ofaf144.

    PMID: 40134634
  3. 3

    EBV VCA IgM and cytomegalovirus IgM dual positivity is a false positive finding related to age and hepatic involvement of primary Epstein-Barr virus infection in children.

    Sohn MJ, Cho JM, Moon JS, et al.

    Medicine 2018; (97(38)):e12380 doi:10.1097/MD.0000000000012380.

    PMID: 30235701
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    The impact of recent Covid-19 infection on cytomegalovirus antibodies.

    Dan W, Yuzhu X, Han W, et al.

    Journal of infection and public health 2025; (18(10)):102848 doi:10.1016/j.jiph.2025.102848.

    PMID: 40614677
  5. 5

    Positive predictive values of CMV-IgM and importance of CMV-IgG avidity testing in detecting primary infection in three different clinical settings. A French retrospective cohort study.

    Périllaud-Dubois C, Bouthry E, Jadoui A, et al.

    Journal of clinical virology : the official publication of the Pan American Society for Clinical Virology 2020; (132()):104641 doi:10.1016/j.jcv.2020.104641.

    PMID: 32947202
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    Potential Biomarkers for Predicting Congenital Cytomegalovirus Infection.

    Tanimura K, Yamada H

    International journal of molecular sciences 2018; (19(12)) doi:10.3390/ijms19123760.

    PMID: 30486359
  7. 7

    Clinical Utility of Viral Load in the Management of Cytomegalovirus Infection in Solid Organ Transplant Patients in Kuwait.

    Madi N, Al-Qaser M, Edan R, Al-Nakib W

    Transplantation proceedings 2015; (47(6)):1802-7.

    PMID: 26293054
  8. 8

    Defining a CMV viral load threshold for pre-emptive therapy in paediatric haematopoietic stem cell transplant recipients.

    Duret A, Charles O, Margetts BK, et al.

    British journal of haematology 2025; (207(3)):911-919 doi:10.1111/bjh.20254.

    PMID: 40630011
  9. 9

    Sensitivity of Dried Blood Spot Testing for Detection of Congenital Cytomegalovirus Infection.

    Dollard SC, Dreon M, Hernandez-Alvarado N, et al.

    JAMA pediatrics 2021; (175(3)):e205441 doi:10.1001/jamapediatrics.2020.5441.

    PMID: 33523119
  10. 10

    Congenital Cytomegalovirus Infection Screening in Newborns From Saliva Samples by Real-Time Polymerase Chain Reaction Analysis.

    Günlemez A, Kolaylı F, Yazıcı Özçelik E, et al.

    Turkish archives of pediatrics 2023; (58(4)):371-375 doi:10.5152/TurkArchPediatr.2023.22309.

    PMID: 37357451
  11. 11

    Amniocentesis to diagnose congenital cytomegalovirus infection following maternal primary infection.

    Dinsmoor MJ, Fette LM, Hughes BL, et al.

    American journal of obstetrics & gynecology MFM 2022; (4(4)):100641 doi:10.1016/j.ajogmf.2022.100641.

    PMID: 35526782
  12. 12

    Epidemiology, risk factors, and outcomes associated with cytomegalovirus in adult kidney transplant recipients: A systematic literature review of real-world evidence.

    Raval AD, Kistler KD, Tang Y, et al.

    Transplant infectious disease : an official journal of the Transplantation Society 2021; (23(2)):e13483 doi:10.1111/tid.13483.

    PMID: 33012092
  13. 13

    Pharmacologic and immunologic management of cytomegalovirus infection after solid organ and hematopoietic stem cell transplantation.

    Meesing A, Razonable RR

    Expert review of clinical pharmacology 2018; (11(8)):773-788 doi:10.1080/17512433.2018.1501557.

    PMID: 30009675
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    Estimating Risks of Central Nervous System Disturbance Associated with Medications for Herpes Zoster: Findings from a Regional Population-Based Cohort Study Using the Shizuoka Kokuho Database.

    Hagiwara R, Nakatani E, Kaneda H, et al.

    Drugs - real world outcomes 2025; (12(3)):399-410 doi:10.1007/s40801-025-00500-2.

    PMID: 40522612
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    Outcome and management of newborns with congenital cytomegalovirus infection.

    Nicloux M, Peterman L, Parodi M, Magny JF

    Archives de pediatrie : organe officiel de la Societe francaise de pediatrie 2020; (27(3)):160-165 doi:10.1016/j.arcped.2020.01.006.

    PMID: 32127242
  16. 16

    Changes in Neutrophil Count During Valganciclovir Therapy for Symptomatic Congenital Cytomegalovirus Infection.

    Kawamura A, Abe S, Shirai K, et al.

    Biomedicines 2025; (13(7)) doi:10.3390/biomedicines13071739.

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  17. 17

    Retrospective study of cytomegalovirus retinitis complicated with acquired immunodeficiency syndrome.

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  18. 18

    CMV retinitis in HIV-infected patients: Plasma viral load utility in diagnosis.

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    PMID: 40446649
  19. 19

    Prevalence and Risk Factors for Cytomegalovirus Retinitis Among People Living with HIV in Sub-Saharan Africa in the Antiretroviral Therapy Era: A Systematic Review and Meta-Analysis.

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    Scientific reports 2026; (16(1)).

    PMID: 42209549

This page explains CMV testing terminology for educational purposes and does not replace professional medical advice. Always consult your healthcare provider to accurately interpret your specific lab results based on your health status.

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