Cytomegalovirus – Serology including Avidity
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This page provides serological testing including avidity testing information for Cytomegalovirus (CMV) at Public Health Ontario (PHO). For information regarding other testing options, refer to Cytomegalovirus – Detection – Real Time PCR.
Updates
- Added information for avidity testing
Testing Indications
CMV serology is most often indicated for diagnosing acute/recent CMV infection, determining evidence of past (latent) infection, and working up infants with suspected congenital infection.
When CMV infection is suspected in a pregnant woman and suspected congenital CMV in a newborn infant, order CMV serology and submit a urine sample for CMV PCR testing. On the PHO requisition form, be sure to request both CMV IgM and IgG. Include all relevant clinical information (e.g. pregnancy, suspected congenital infection, etc.), onset date and signs and symptoms.
CMV IgG avidity is both a sensitive and specific method for identifying pregnant women with recent primary CMV infection and thus at increased risk for vertical CMV transmission. The test is automatically conducted at PHO’s laboratory for pregnant patients with a positive CMV IgG and IgM serology test ordered.
Acceptance/Rejection Criteria
Donor testing is not available through PHO’s laboratory. Specimens from patients being screened as potential donors (e.g. organ, tissue, cells, fertility, etc.) should be referred to a laboratory that performs donor screening assays. Specimens received for donor screening at PHO’s laboratory will be rejected.
Specimen Requirements
| Test Requested | Required Requisition(s) | Specimen Type | Minimum Volume | Collection Kit |
CMV IgG CMV IgM +CMV Avidity |
Serum |
1.0 ml |
Blood, clotted – Serum separator tube (SST) |
|
CMV IgG CMV IgM +CMV Avidity |
Whole Blood |
5.0 ml |
Blood, clotted – Serum separator tube (SST) |
Submission and Collection Notes
Complete all fields of the requisition form, including:
- Test(s) requests and indications for testing
- Patient setting, specimen type and source
- Patient clinical history, vaccination history, signs and symptoms
Label the specimen container(s) with the patient’s first and last name, date of collection, and one other unique identifier such as the patient’s date of birth or Health Card Number. For additional information see: Criteria for Acceptance of Patient Specimens. Failure to provide this information may result in rejection or testing delay. Refer to Serology Testing – Laboratory Specimen Collection and Submission Instructions for more information.
CMV IgG testing will be performed on all requests for CMV immunity serology.
CMV IgG and IgM testing will only be performed on diagnostic requests when the following clinical information is provided on the General Test Requisition Form indicating acute/recent infection, vaccination history, relevant signs, symptoms, and/or clinical history, and onset date. This information assists in providing the correct interpretation of results.
CMV IgG avidity will be performed automatically in a pregnant patient with CMV IgG and IgM positive.
All other patients with CMV IgG and IgM positive would require a request to the lab to perform avidity.
CMV IgG avidity testing should be ordered alongside CMV IgG and IgM tests, as it depends on the outcome of serology results. NO CMV avidity testing will be performed on the following patients:
- CMV IgG and IgM negative
- CMV IgG positive but IgM negative
- CMV IgG negative regardless of IgM result (CMV avidity testing is dependent on the presence of detectable IgG and therefore cannot be performed if IgG is not detectable).
Timing of Specimen Collection
Acute: Collect the acute specimen within 7 days after the onset of symptoms.
Convalescent: Collect the convalescent specimen 7 to 10 days after the acute phase.
Limitations
Haemolysed, icteric, lipemic or microbially contaminated sera or plasma are not recommended for testing.
Please be aware that the assay used for the detection of CMV IgG & IgM has not been validated for screening potential donors including organs, tissues, cells, bone, corneas, fertility, etc. using serum or plasma samples.
Exceptions are:
- Bone marrow donors and living-related donors who are otherwise healthy people will be tested.
- Transplant Recipient work-up assessment will be tested.
Storage and Transport
Centrifuge if using SST. Place specimen in a biohazard bag and seal. Specimens should be stored at 2-8°C following collection and shipped to the PHO’s laboratory on ice packs as soon as possible.
All clinical specimens must be shipped in accordance to the Transportation of Dangerous Good Act.
Test Frequency and Turnaround Time (TAT)
CMV Diagnostic IgM and IgG serology is performed daily Monday to Friday. TAT is up to 5 business days from receipt at the PHO’s laboratory.
CMV IgG avidity is performed once a week on an as-needed basis.
The CMV IgG and IgM tests are performed using Chemiluminescent Immunoassay (CLIA) technology on the Diasorin LIAISON® XL for the qualitative determination of IgG and IgM antibodies to human cytomegalovirus (hCMV) in human serum.
The LIAISON® CMV IgG assay is intended to be used as an aid in the determination of serological status to CMV.
The LIAISON® CMV IgM assay is intended to be used as an aid in the diagnosis of acute CMV infection.
Test results are reported qualitatively together with a clinical interpretation based on the status of both IgM and IgG.
The CMV IgG Avidity is performed using the Enzyme immunoassay (ELISA) technology on the Euroimmun for the in vitro determination of human antibodies of the immunoglobulin class IgG against CMV in serum to support the diagnosis of infections with cytomegalovirus. The product is designed for use as an in vitro diagnosis (IVD).
Performance characteristics of this assay have not been established for testing pediatric and newborn populations or cord blood specimens.
Interpretation
CMV Serology
Antibody levels may be reported as Non-Reactive (no detectable antibody), Indeterminate (the level of antibody detected is considered borderline reactive or equivocal) or Reactive (antibody is detectable within the positive range of the assay).
Non-Reactive and Indeterminate levels of both IgM and IgG antibodies may be observed in the early acute stage of infection. The levels will increase to reactive levels in subsequent weeks.
In the absence of acute/recent infection, indeterminate levels of IgG may represent very low levels of antibody many years after the initial infection whereas indeterminate levels of IgM may be due to declining levels of IgM several months post infection or occasionally as a result of assay non-specificity. In some patients persisting low levels of CMV IgM have been observed many months (> 6 months) after primary infection.
Assays for IgM antibody lack specificity for primary infection due to false-positive results, because of persistent IgM for months after primary infection, and because IgM may be positive in reactivated CMV infections.
If the acute blood sample shows a low reactive, indeterminate or non-reactive IgG and/or IgM result, a convalescent sample should be collected at least 10 to 14 days later. Recent infection is confirmed if a significant rise in antibody levels is observed between acute and convalescent sera.
CMV IgG Avidity
The presence of low avidity antibodies in a patient’s serum has been proved if the ELISA extinction value is considerably reduced by urea treatment. In order to objectivate the results a relative avidity index (RAI) is calculated and expressed in percent using the extinction values with and without urea treatment. The upper limit of range of low-avidity antibodies (cut-off value) recommended by EUROIMMUN is 40% RAI. Values below the indicated cut-off are to be considered as an indication of low-avidity antibodies. Values between 40% and 60% RAI as equivocal, values above 60% as an indication of high-avidity antibodies.
A positive result should be interpreted together with clinical findings and results from other serological tests. The results obtained from this assay are not diagnostic proof of the presence or absence of a disease.
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