Mononucleosis also known as Mono or Kissing Disease is due to infection caused by the
Epstein Barr Virus leading to symptoms of fever, sore throat, and large cervical lymph
nodes.
When mono is suspected in a patient, a rapid
monospot test can be performed.
This test begins by removing the test cartridge
from its pouch and placed on a flat surface.
Whole blood is then obtained either from a
finger stick or anticoagulated blood professionally obtained.
Here, blood has been obtained via needle stick.
Place 1-2 drops of bleed into the cartridge’s
sample well.
2-3 drops of Developer Solution containing
a phosphate saline buffer is then added to the sample well.
The results are read after 8 minutes.
Here is an 8 minute rapid time lapse showing
a negative mono test result.
Note that the red arrow points to the presence of single red control band indicating a valid
test.
Given the absence of a second band, this test would be considered negative and the patient
would not be considered to have mono.
Here is an 8 minute rapid time lapse showing
a positive Monospot result.
The red arrow points to the control band to ensure the test is valid.
If this red band is absent, any test results whether negative or positive would be considered
erroneous and needs to be repeated.
The blue arrow points to a second band that
should appear if mono is present indicating a positive mono spot test.
As such, if TWO bands are present, the patient has mono and should be treated accordingly.
So how does this test work?
In essence, this test runs the liquid sample
along the surface of a pad with reactive molecules that show a visual positive or negative result.
The pads are based on a series of capillary beds which has the capability of transporting
fluid spontaneously via capillary action like a sponge.
This testing technique is called solid phase
lateral flow immunoassay.
In the image below, Mono heterophile antibodies
is depicted as a purple circle, bovine erythrocyte extract is the yellow letter Y with the yellow
circle being a pigment, and mouse anti-human IgM antibody is shown as a plain green letter
Y.
The plain white letter Y is the control.
In the monospot test, the test pad has been
pre-coated with mouse anti-human IgM antibody only in the test band region.
When the sample well is exposed to blood,
it gets absorbed into the test strip pad where it mixes with the bovine erythrocyte extract.
If the specimen contains Mono heterophile
antibodies (or purple circle), the bovine erythrocyte extract binds to the Mono antibodies
and drags it across the test strip via capillary action.
When the antibody-bovine extract complex encounters
the mouse anti-human IgM antibody immobilized in the test region, it produces a colored
test band and indicates a positive result.
To serve as a test control, a colored band
will also appear in the control region if the test has been properly performed which
encompasses any free bovine erythrocyte extract not captured in the test region.
Obviously, there is many more bovine erythrocyte extract so even if Mono is present, there
will always be unattached bovine erythrocyte extract to allow for a positive control band.