Laboratory investigation of glandular fever may not be necessary where the patient’s clinical features suggest a diagnosis.
Testing is recommended, however, wherever the clinical picture is unclear or an incorrect diagnosis has the potential
to cause significant morbidity. Women who are pregnant and people who are immunocompromised should always have laboratory
investigations requested, as the consequences of a missed diagnosis of acute HIV, toxoplasmosis or cytomegalovirus infection
are more significant and may result in adverse foetal outcomes and increased morbidity and mortality.
When testing is indicated, the recommended tests are a full blood count (FBC) and a heterophile antibody test, followed
by serology if the diagnosis remains unclear. Viral culture is not performed for diagnosis. (See below
for specific recommendations for testing in children, older adults, women who are pregnant and people who are immunocompromised).
Start with a full blood count and a heterophile antibody test
A full blood count, when combined with findings from a clinical examination, can be highly suggestive of glandular fever.
The white blood cell count in a person with glandular fever averages between 12 – 18 x 109/L, with more than
50% being mononuclear lymphocytes.1,6 Atypical lymphocytes appear in the first week of symptomatic illness,
increase to more than 20% of the total white blood cell count in the second week, and then decline over several weeks.
A blood film with at least 10% atypical lymphocytes in a symptomatic person has a sensitivity of 75% and a specificity
of 92% for the diagnosis of infectious mononucleosis, although not necessarily EBV infection.1,7 The differential
diagnosis of atypical lymphocytosis includes acute viral infections, toxoplasmosis and drug hypersensitivity reactions.
Glandular fever is unlikely in a patient with a normal or reduced total white blood cells and lymphocytes, but patients
who are tested within one week of symptom onset are less likely to have increased atypical lymphocytosis.
Heterophile antibody tests are used to confirm that glandular fever is due to acute EBV infection and
to therefore rule out other causes of raised atypical lymphocyte counts.
Heterophile antibodies are a group of immunoglobulin M (IgM) antibodies induced by acute EBV infection that react to
red blood cell antigens from other species. Heterophile antibodies are present at clinically significant levels by the
time of symptom onset and peak between two and five weeks later. Identifiable levels of heterophile antibodies may persist
in a person with glandular fever for up to one year.
The presence of heterophile antibodies in a symptomatic adolescent or young adult has a sensitivity of approximately
90%, and specificity of almost 100% for glandular fever.3 However, false-negatives occur in 25% of people early
in the course of their illness (e.g. in the first week).1 False-positives rates of 2 – 3% may be seen in patients
with HIV infection, rubella, systemic lupus erythematosus and leukaemia, and older people or women who are pregnant.
Heterophile tests may be listed on laboratory request forms as Monospot, heterophile antibodies, infectious mononucleosis
screen or Paul-Bunnell.
Throat swabs for pharyngitis should be taken where there is doubt about the differentiation of glandular
fever from streptococcal pharyngitis. Practitioners should take into account the incidence of rheumatic fever in their
area, and the likelihood of adverse sequelae of a missed diagnosis of streptococcal pharyngitis. The New Zealand sore
throat guidelines state that the threshold for throat swab should be lower in a symptomatic patient with two or more of
the follow features:5
- Māori or Pacific ethnicity
- Age 3 – 45 years (with the highest pre-test probability of a positive result in the age 3 – 14 year group)
- Living in lower socioeconomic areas of the North Island
- Past history of rheumatic fever
However, a positive result for streptococcus on a throat swab does not indicate whether there is an active infection
or asymptomatic carriage, in which case glandular fever is still possible. Approximately 30% of people with primary glandular
fever will have a non-symptomatic streptococcus carriage.1
Liver function tests are not routinely recommended as a diagnostic test for glandular fever. Tests are abnormal in more
than 80% of people with glandular fever, but acute liver failure associated with EBV is very rare.8 In addition,
abnormalities in liver tests can be expected in all forms of infectious mononucleosis and in many other illnesses.
Liver tests should be considered for patients presenting with jaundice or significant hepatomegaly.2 If measured,
aspartate transaminase (AST) and alanine transaminase (ALT) levels more than ten times the upper limit of normal indicate
that glandular fever is unlikely, and acute viral hepatitis should be considered.7 Normal liver tests do not
exclude glandular fever.
Where the diagnosis remains unclear, serology is recommended
If an initial FBC and heterophile tests fail to indicate glandular fever, specific EBV serology may be requested. Alternatively,
FBC and heterophile tests may be repeated after seven days, followed by EBV serology if results are inconclusive.9
EBV serology tests provide a stage-specific diagnosis. The majority of the population is seropositive, so identifying
a primary infection is important. The tests measure the activity of three kinds of antibody: viral capsid antigen (VCA)
IgM and VCA IgG antibodies and anti-EB nuclear antigen (EBNA) antibodies.
VCA IgM antibodies are usually present at clinical levels from the outset of symptoms of glandular fever, and persist
for two to four months before declining (Figure 1).3 VCA IgG antibodies appear later than VCA IgM antibodies
but persist for a much greater time, often for life.3 EBNA antibodies appear six to twelve weeks after the
onset of symptoms and also persist for life.3
The absence of EBNA antibodies indicates that the person has not had a previous glandular fever infection. VCA IgM and
VCA IgG antibodies can then indicate if there is a current infection. An avidity test on the VCA IgG antibodies gives
an indication of the time since infection – low avidity indicates recent infection and high avidity more than six to eight
weeks since the acute infection.
The presence of EBNA antibodies indicates previous EBV infection. In a non-immunocompromised person this excludes acute
EBV infection as an explanation for the current symptoms. In this case the initial diagnosis should be reconsidered, and
other potential causes of infectious mononucleosis investigated.
Testing in older adults, children and people who are immunocompromised or pregnant
Specific EBV serology and FBC are recommended as the first-line tests for women who are pregnant, people who are immunocompromised,
children and older people. Heterophile antibody tests are not necessary (and are also not used in children).
People who are immunocompromised and women who are pregnant should have specific EBV serology tests. It is necessary
to confidently exclude other forms of infectious mononucleosis, as they are associated with adverse foetal outcomes.1 Given
the risks associated with primary cytomegalovirus and toxoplasmosis during pregnancy and the risk of mother-to-child transmission
of HIV, definitive testing for other causes of infectious mononucleosis (i.e. tests for cytomegalovirus, toxoplasmosis
and HIV) is also indicated in pregnant women presenting with infectious mononucleosis.1
Children and older adults require serology testing because heterophile antibody tests are less accurate outside of the
age 12 – 25 year group. Heterophile antibody tests are likely to be falsely-negative in 50 – 75% of children, and older
adults may remain reactive from a past infection or be falsely positive.1