Pathology Associates Of Lexington, P.A.

CMV, Blood Test

Cytomegalovirus blood antibody tests

CMV is an important human pathogen and one of the family of herpes viruses, being HHV-5. Infection is widespread and usually asymptomatic. It is relatively frequently a disease of newborns, sometimes severe. CMV can be a congenital infection, a perinatal infection, or a postnatal (adult) infection. We use the IFA test method. Patient serum sample is serially diluted (IgM begins at 1:10 and IgG at 1:20) and reacted with Zeus Scientific CMV-infected human fibroblast cells (50-70% of cells infected), the cells having been reagently affixed on microscope slides. If patient-generated anti-CMV antibodies are in the serum sample, they will bind to the antigen substrate and will not be rinsed off. Reagent anti-human-globulin IgM tagged with fluorescein (FITC anti-IgM IgG) is added to the test slide, and it will bind to any already-bound patient antibodies. The medical technologist or pathologist then microscopically discerns any positive reaction as cytoplasmic AND nuclear positive fluorescence. Golgi-region-only positivity is not related to CMV.

CMV causes an infectious mononucleosis syndrome which, like EBV IM, produces atypical peripheral blood lymphocytosis and with similar throat and other symptoms. But the monospot test is negative. [warning] It can also complicate immuno-suppressed patients. It can be detected by PCR in distant reference labs.

Antibody reactions:
- in immunocompromised adults, this serological testing is often unreliable because population positivity prevalence is so high and reactivated CMV likely not to elevate titers²
- IgM: nuclear and cytoplasmic positivity at 1:10 or higher
- IgG: nuclear and cytoplasmic positivity at 1:20 or higher
Interpretation:
- Active infection: IgM titer positive at 1:10 or higher (IgM can commonly continue to be detected to around 6 months⁴; around 24% of cases carry positivity at <1:16 for 12 months³
- Immune status, previously infected: IgM negative and IgG positive at 1:20 or higher
- False positive IgM: if lab fails to correct for patient rheumatoid factor or positive ANA or fails to insist on nuclear AND cytoplasmic positivity
- False positive IgG: if lab fails to correct for patient positive ANA
CMV Diseases:
- Congenital CMV inclusion disease (CID):
  - Incidence: 0.5-2.5% of deliveries
  - 95% clinically asymptomatic, but may have sequelae:
    - 10-25% may develop hearing loss
    - 5-10% may exhibit variable degrees of mental retardation or CNS motor disorders
  - 5% Symptomatic:
    - Panifested variously as:
      - severe disease with jaundice
      - hepatosplenomegally
      - thrombocytopenic purpura
      - cranial calcification with growth retardation, pneumonitis, hydrocephaly and ocular defects
    - Prognosis: some expire shortly after birth of complications, but most survive with concurrent CNS damage
- Perinatal CMV: almost always asymptomatic
- Postnatal CMV:
  - majority are asymptomatic
  - AIDS-associated pneumonia [L10-11625].
  - CMV-type infectious mononucleosis syndrome (like EBV IM) but more likely to include hepatitis
  - pulmonary CID with hepatitis (usually immunosupressed or immunodeficient patients)
  - colitis³
- Organ transplant Recipients: a CMV negative recipient engrafted with organ tissue from a CMV positive donor is at much higher risk for acquisition of CMV disease and graft failure (and this includes blood transfusions to these patients AND to premature babies)².

References:

Lexington Medical Laboratories, West Columbia, SC, procedure manual (primary references therein)
Laboratory Medicine..., Howanitz and Howanitz, 1991, page 816
Interpretation of Diagnostic Tests, Wallach, 2000, 7th Ed., pages 841-842.
Carter, JB & Carter, SL workshop handout ca. 1980.