CBC, CHEMISTRY, URINALYSIS, AND BONE MARROW
A CBC can be performed on whole
blood, revealing a non-regenerative
anemia, often severe, together with a lymphopenia.
and thrombocytopenia can also be seen
from bone marrow suppression or
immune mediated destruction. Red cells reveal increased nucleated
cells in circulation and a macrocytosis,
with or without an appropriate
reticulocytosis. Chemistry results
can reveal azotemia,
hyperbilirubinemia, bilirubinuria, and increased liver enzymes.
proteinuria with golmerulonephritis can be found on
Arrest of the bone marrow occurs causing erythrodysplasia
bone marrow aspiration or biopsy can be performed to check if
hypocellular bone marrow exists(8).
Testing for the FeLV antigen is the most effective way to
spread of the virus. Vaccines should not be a substitute for
testing. Always test before giving a vaccination (3), to ensure
that an infected cat is not being vaccinated. An infected cat
will not respond to the vaccine. If the tested cat does reveal a
FeLV positive test, then appropriate steps can be taken to minimize
are 2 main tests that can be done to detect FeLV positive cats.
They detect the
FeLV antigens, not the anti-FeLV antibodies produced by the cat.
Maternal antibodies and
vaccines also do not interfere with testing (3).
IFA (ImmunoFluorescent Antibody) –
IFA detects the
structural core antigen p27 within the cytoplasm of blood cells
(leukocytes and platelets) (3). This cannot be done in house and
must be sent to a commercial laboratory (4). Peripheral blood
smears are made using whole blood or the buffy coat and then
analyzed. Cytologic preparations of bone marrow can also be used
(8). IFA is not found positive until AFTER the bone marrow is
affected (2). Therefore, this test is used for prognostic reasons
or to confirm a positive result with the ELISA test and suspicious
samples (3). 97% of IFA positive cats remain persistently
infected, contagious, and viremic for
Method of Detecting Feline Leukemia
ELISA (Enzyme Linked ImmunoSorbent
Assay) – ELISA
detects the core p27
well as free soluble FeLV p27 in plasma
or serum (3). It is usually found in
the form of in-house test
kits. Most test kits have a sensitivity and specificity of 98%
colour change from the immunoglobulin reaction results in
a positive sample.
Whole blood, plasma, serum, saliva, or tears
can be used, although the latter two are
not reliable (2). ELISA
tests can be run to diagnose infections PRIOR to the infection
marrow. Therefore, FeLV can be detected in the early stages of
self-limiting infections even if the IFA test is
negative. A single positive
predict which cats will
be persistently viremic; the cat must be
retested in 12 weeks
ELISA Snap Test
If ELISA positive cats revert to
or a sequestered
RESULTS OF IFA AND ELISA (3)
Accuracy can be improved by running both ELISA and
IFA tests together.
A positive ELISA cat should be retested 6 weeks
after the initial test. If still positive, then a retest is
performed on the cat after 10 weeks. If
positive on the third
test then the cat is most likely persistently
viremic and positive for
A positive ELISA cat can be immediately tested with
the IFA test and if also found positive a transient infection is
least likely (3-9%).
- A positive ELISA
is more likely to convert to
negative than cats with a positive IFA test.
- If a repeated
ELISA test is positive and the IFA
test is negative there is most likely a focal infection kept localized
by the immune system.
- A negative ELISA
and positive IFA is always false.
- Blood smears
too thick can create false positives (2).
- False negatives
occur with a leukopenia or
thrombocytopenia. This is due to
the evaluation of an
number of cells (2).
PCR can be performed as
confirmatory tests for latent or sequestered infections.
All sick cats,
new cats to be introduced to a household, exposed cats,
and high risk groups should be tested for FeLV. Keep in mind that
no test is 100% accurate;
results should be interpreted in light of
the patient’s health and prior exposure to FeLV (3).
Cytologic exam of fine needle aspirates of masses, lymph nodes,
cavity fluids, or affected organs can reveal malignant
lymphocytes. A bone marrow exam can
involvement even when peripheral blood appears normal. A biopsy
and histopathology is often necessary for a diagnostic confirmation of
Neoplasia in a cat