Pathology Associates Of Lexington, P.A.
Pathology Associates Of Lexington, P.A.
Pathology Associates Of Lexington, P.A.
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Epstein-Barr virus, blood antibody tests
EBV is a ubiquitous herpes-type DNA virus (HHV-4) considered to be the causative agent in a number of illnesses. About 50% of children in industrialized countries (90% in 3rd world) have been asymptomatically infected by teenage years. Teenage primary infections are 50% as infectious mono (IM) syndrome. Specific clinical diagnosis is most commonly made using a screening "monospot" test (based on the Paul-Bunnell agglutination test detecting a "heterophile antibody" originally directed toward sheep RBCs, Paul-Bunnell-Davidsohn test...then to modified horse RBCs, Lee-Davidsohn test...after patient's test-serum adsorption by guinea pig kidney [Forssman] antigens...such Ab being present in 90%7 of EBV cases) in cases presenting as "infectious mononucleosis" (IM). EBV serology is most helpful in the 10-30% of instances of initially "heterophile test negative" EBV-mono (only 7% remain heterophile neg. throughout illness4).  And, where desired, this more specific test certainty is obtained using serological IFA tests of antibodies in patient serum diluted 1:10 vs. various EBV antigens (Ag) present in a reagent substrate of a EBV-infected cell line (the VCA [viral capsid antigen] test is our current serological screen).

We use the IFA method. Patient serum sample is serially diluted (IgM begins at 1:10 and IgG at 1:20) and reacted with an EBV-infected HRIK Burkitt's lymphoma cell line (5-10% of the cells are infected), the cells having been reagently affixed on microscope slides. If patient-generated anti-EBV 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 for VCA. Other components of a full EBV profile are now done in a reference lab when especially needed. [warning]

By the way, Lab Corp apparently uses ELISA/EIA-type methods for their testing...reported in "units" of reactivity. We do not know how the units might compare to these classical dilutional conventions of IFA reporting.

  • Antibodies develop to these viral antigens:
    • VCA (viral capsid antigen):
      • IgM rises very early, peaks about 2nd week (3rd-4th week6) of illness & drops, replaced by IgG, becoming undetectable within 1-2 months (that is, shortly after illness subsides)...indicates infection2; may persist 6 months and can get a false positive in some cases of CMV5
      • IgG peaks in about 3rd-4th weeks6 of illness and lowers to levels which persist many years
      • IgA increase said to be a screen for NP carcinoma
      • IgM false positives: some "low/low-type" CMV cross-reactivity; failure of a lab to absorb out a patient's rheumatoid factor (an IgM anti-IgG); ANA positivity misinterpreted as EBV positivity
      • IgG false positives: ANA positivity misinterpreted as EBV positivity
    • EA (early Ag) (there are diffuse and restricted variants, EA-D & EA-R)
      • IgM...n/a
      • IgG EA-D appears within weeks, this is present for several months (can persist for several years), then reverts to undetectable
      • persistently elevated titers may reflect EBV-type chronic fatigue syndrome.
      • elevated titers in cases of NP carcinoma3; EA-D5
      • elevated titers of EA-R in Burkitt's5
    • EBNA (Epstein-Barr-associated nuclear Ag):
      • IgM...n/a
      • IgG may appear in 4th-8th weeks of illness...detectability often delayed 6 months, presence signals convalescence,  and detectibility persists for life
      • absence of, or low detectibility after at least 6 months post a definite EBV infection may indicate EBV-type chronic fatigue syndrome; or,
      • absence usually indicates lack of previous infection; or,
      • some immunocompromised definitely prior EBV-positive patients demonstrate diminishing or absent EBNA
    • MA (early and late7 EBV-coded cell-membrane Ags)
      • IgM
      • IgG in several weeks and persists for life
  • Interpretation:
    • acute disease
      • IgM VCA detected & reaches high titer2; present in 100% of infections3
      • IgG VCA detected & reaches high titer; a 4-fold increase means active disease, a single test of 1:320 is strongly suggestive & 1:640 or higher is diagnostic of current/recent infection
      • EA appears
    • current "infection" or viral loaded
      • elevated EA
    • convalescent phase:
      • begins with detection of EBNA and shift from undetected to rising indicates primary infection
    • past infection (immune status)
      • IgG VCA detected
      • EBNA detected and persists for life
      • EA has reverted to undetectable
    • re-infection (spontaneous or in immunocompromised) or reactivation
      • VCA IgM so briefly detectible that usually missed
      • VCA IgG can increase over immune status baseline
      • EA reappears
    • chronic EBV (fatigue) syndrome:
      • high IgG EA which has often become the EA-R7 type.
      • high IgG VCA (no lower than 1:320; safer to diagnose at 1:640-1:1280 or higher4) [our standard practice is to propose the comprehensive profile only when IgG VCA is = to or >1:1280]
      • EBNA may be in very low titer (undetected or positive at only 1:2-1:44; less than 1:55)
  • EBV diseases:
    • EBV-mono "infectious mononucleosis" (IM)
    • nasopharyngeal carcinoma
    • nearly 100% of African Burkitt's lymphoma
    • about 20% of non-African Burkitt's lymphoma
    • B-cell lymphoma in immunocompromised patients
    • CMV-like disease in renal transplant recipients
    • post-transfusion syndrome
    • some cases of chronic fatigue syndrome

References:

  1. Medical Microbiology [text], Jawetz, et. al, 22nd Ed., 1995, page 386-389.
  2. ABC's of Interpretive Laboratory Data [text], Seymour Bakerman, 2nd Ed., 1990, page183-184.
  3. Laboratory Medicine: Test Selection and Interpretation [text], Howanitz & Howanitz, 1991, page 816-817.
  4. Carter, JB & Carter, SL  workshop handout  ca. 1980.
  5. Interpretation of Diagnostic Tests, Wallach, 2000, 7th Ed., pages 843-847.
  6. Lexington Medical Laboratories, West Columbia, SC, procedure manuals (containing primary references).
  7. Principles & Practice of Infect. Diseases, Mandell, Douglas, and Bennett, 3rd Ed., p1172-1185 (EBV chapter by Schooley)...SKBL lab manual p. 256.

(posted 2000; latest addition 31 March 2005)

 
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