Cytomegalovirus – Serology

Testing Indications

Cytomegalovirus (CMV) serology is most often indicated for the diagnosis of acute/recent CMV infection, to determine evidence of past (latent) infection, and in the work-up of infants with suspected congenital infection.

When CMV infection is suspected in a pregnant woman please order CMV serology and also submit a urine sample for virus detection. Be sure to indicate on the PHO laboratory requisition that the patient is pregnant and clearly request both CMV IgM and IgG. Include all relevant clinical information (Onset Date and Symptoms).

When congenital CMV is suspected in a newborn infant and serology is requested please clearly indicate that both CMV IgM and IgG is required and also submit a urine sample for virus detection.

Include all relevant clinical information such as onset date and symptoms.

Specimen Collection and Handling

Specimen Requirements

Test Requested Required Requisition(s) Specimen Type Minimum Volume Collection Kit

CMV IgG and/or CMV IgM

Whole blood or serum

5.0 ml whole blood or 1.0 ml serum

Blood, clotted – vacutainer tubes (SST)

CMV IgG and/or CMV IgM

Plasma

5.0 ml

EDTA Lavender top tube

Submission and Collection Notes

1

CMV IgG testing will be performed on all requests for CMV serology

2

CMV IgG and IgM testing will only be performed when the following clinical information is provided on the General Test Requisition Form indicating acute/recent infection, relevant signs, symptoms, and/or clinical history, and onset date.

Timing of Specimen Collection

Acute: Collect the acute sample within 7 days after the onset of the rash

Convalescent: Collect the convalescent sample 7 to 10 days after the acute

Limitations

Haemolyzed, 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 IGM has not been validated for screening potential donors including organs, tissues, cells, bone, corneas, etc. using serum or plasma samples.

Preparation Prior to Transport

Label the specimen container with the patient’s full name, date of collection and one other unique identifier such as the patient’s date of birth or Health Card Number. Failure to provide this information may result in rejection or testing delay.

Special Instructions

Centrifuge if using SST. Place specimen in biohazard bag and seal. Specimens should be stored at 2-8°C following collection and shipped to the PHO laboratory on ice packs as soon as possible.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

CMV Diagnostic IgM and IgG serology is performed daily Monday to Friday.

Turnaround time is up to 5 days from receipt by PHO laboratory.

Reporting

Results are reported to the ordering physician or health care provider named on the requisition.

Test Methods

The CMV IgM and IgG tests are performed using ELISA (Enzyme Linked Immunosorbent Assay) test kits manufactured by Euroimmun Diagnostics (Germany). Both assays measure human antibodies of the IgM and IgG classes against CMV in serum or plasma. Test results are reported qualitatively together with a clinical interpretation based on the status of both IgM and IgG.

After a primary infection, both IgM and IgG antibodies develop within approximately 3-7days after onset of symptoms. Both antibodies subsequently increase reaching a plateau 2-3 weeks later.

The presence of IgG antibody (in asymptomatic persons) provides evidence of past infection and therefore indicates evidence of latent infection and immunity to re-infection.

In symptomatic patients, indeterminate levels of antibody may indicate rising antibody levels following acute/recent infection. In asymptomatic patients indeterminate levels of antibody may be due to genuinely low levels of IgG antibody many years after the initial infection.

Interpretation

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.

For more information on the interpretation of serological results refer to the document titled: LAB-SD-044, Diagnostic Interpretation of Viral Specific IgM and IgG Serology.

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Updated 22 Oct 2019