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Clinical Pathology Laboratory - Available
Test
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Antinuclear Antibody Testing
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Antinuclear antibodies (ANA) are auto-antibodies against nuclear
components, including double and single stranded DNA and histones.
These antibodies can be detected with an ANA test. In this technique,
a fluorescent-labeled immunoglobulin is used to detect immunoglobulin
in the patient's serum against nuclear components.We currently use
rat liver as a source of nuclear components. Patient sample in sequential
dilutions (to obtain an ANA titer) is incubated with rat liver. If
there are antibodies against nuclear components, these will bind to
the nuclei in the liver. The bound antibodies can then be detected
using a secondary fluorescent-labeled antibody against the species-specific
immunoglobulin with fluorescent microscopy. Different immunofluorescent
patterns can be seen such as homogenous (shown on the left), speckled
and nucleolar. However, in the dog, these patterns are not specific
for a particular antibody or disease. The test requires the use of
species-specific fluorescent antibody, which we only have for the
dog and cat.
The ANA test is used specifically for the diagnosis of systemic
lupus erythematosis (SLE). A positive ANA titer (> 1:80) with
the associated clinical signs (e.g. skin disease, polyarthritis)
and laboratory findings (e.g. proteinuria, thrombocytopenia) is
diagnostic for SLE. ANA tests are used to support a diagnosis of
SLE, but it must be realised that positive results can be seen in
a variety of conditions, other than SLE, including infectious and
non-immune-mediated inflammatory disease. Some people use the ANA
titer to support an immune-mediated pathogenesis in a variety of
other diseases. For example, dogs with immune-mediated non-regenerative
anemias often have high ANA titers (usually < 1:160), despite
not having SLE.
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| Our results are reported out as a titer, with the following
guidelines: |
| Titer |
Interpretation
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| Negative |
Normal result. Most healthy dogs have negative titers |
| 1:20 to 1:80 |
Low positive titer. This is not diagnostic of SLE. Such titers
can be seen in a variety of immune-mediated and inflammatory
conditions. |
| > 1:80 |
High positive titer. This is supportive of SLE (when used
in conjunction with clinical signs and other laboratory results) |
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| Note that corticosteroid therapy will affect an ANA
titer. However, if clinical signs are still evident, despite corticosteroid
therapy, it is unlikely the ANA titer will be affected by the drug
therapy. |
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