Reference range for both analytes (Heterophile IgM, VCA IgM):
  0.8 AI or less: Negative
  0.9-1.0 AI: Indeterminate
  1.1 AI or greater: Positive

This panel consists of two tests for acute EBV infection:
   Heterophile IgM antibodies
   Viral capsid antigen (IgM) antibody

Epstein-Barr virus (EBV) is the etiologic agent of infectious 
mononucleosis. EBV infection can be difficult to diagnose by 
laboratory testing; however, the majority of acute infections can be 
recognized by testing the patient's serum for heterophile antibodies 
(e.g., by the "Monospot" latex agglutination assay), which usually 
appear within the first 3 weeks of illness, but then decline rapidly 
within a few weeks. Heterophile antibodies are found in a very high 
percentage of infants and older children with acute mononucleosis.  
However, heterophile antibodies do not develop in approximately 10% of 
adults.  Presence of VCA IgM antibodies indicates recent primary 
infection with EBV.

Infection with EBV usually occurs early in life, typically as 
infectious mononucleosis. Other disorders due to EBV infection have 
been recognized, including Burkitt's lymphoma and nasopharyngeal 
carcinoma. EBV infection may also cause lymphoproliferative syndromes, 
especially in patients who have undergone renal or bone marrow 
transplantation and in those who have AIDS. 

Acute EBV infection usually shows either:
   Heterophile IgM positive / VCA IgM positive or
   Heterophile IgM negative / VCA IgM positive

Heterophile IgM is relatively less sensitive than VCA IgM in acute EBV 
infection.  The pattern of heterophile IgM positive / VCA IgM negative 
is very uncommon and difficult to interpret.