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Clinical Pathology Laboratory - Available Test
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Immunoglobulin Measurement
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| Measurement of individual immunoglobulins is performed for 2 reasons: |
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Detection of immunodeficiency |
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- The most commonly used test is measurement of IgG in foals,
llamas and calves for failure of passive transfer. There are many
different immunodeficient states that have been reported in animals.
Some are inherited, , e.g. severe combined immunodeficiency in
Basset Hounds and Arabian or Arabian cross horses, whereas others
are acquired, e.g. selective IgM deficiency in horses with lymphoma.
For more information on these, please refer to the Globulin section
of our Chemistry Module.
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Determination of the nature of a paraprotein in monoclonal gammopathies |
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- Monoclonal gammopathies are a group of disorders that are characterized
by the clonal proliferation of B-lymphocytes. These cells secrete
large amounts of a single immunoglobulin, which can result in
clinical signs of excessive bleeding, renal failure and hyperviscosity.
In dogs, monoclonal gammopathies occur typically with lymphoid
neoplasia, especially multiple myeloma, chronic lymphocytic leukemia
and lymphoma. In addition, monoclonal gammopathies can be idiopathic
or occur secondary to canine Ehrlichiosis, Leishmania infection,
or chronic pyoderma. In most of these reactive plasma cell proliferations,
the monoclonal immunoglobulin is IgG, whereas IgG, IgM or IgA
can comprise the monoclonal protein in the neoplastic conditions.
Therefore, quantification of the immunoglobulin class in a documented
monoclonal gammopathy (by serum protein electrophoresis) is essential
for the differential diagnosis of these conditions. In neoplastic
conditions such as lymphoma and multiple myeloma, excessive amounts
of a single immunoglobulin are produced. The type of immunoglobulin
involved can be determined by quantifying the different immunoglobulins
using radial immunodiffusion (see below). Therefore, RID should
only be performed after a monoclonal gammopathy has been confirmed
on serum protein electrophoresis.
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Bone marrow cytology in a dog with multiple myeloma. There are large
numbers of plasma cells (*) in the aspirate, some of which are binucleate.
Hematopoietic cells (both myeloid [M] and erythroid [E]) are found
in normal numbers and maturation sequence. |
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In the past, immunoelectrophoresis was used to detect the immunoglobulin
class, however this test is qualitative, insensitive, and cumbersome.
It has been replaced by immunoglobulin quantification by single radial
immunodiffusion (RID), which we use here at Cornell University. In
this technique, agarose gel is impregnated with antibody against the
species-specific immunoglobulin. The patient's serum is placed in
a well and diffuses through the gel. When a zone of antibody-antigen
equivalence is reached, a precipitin ring forms. This takes up to
48 hours to occur. The width of the ring is compared to a standard
curve run on the same gel and is converted into a immunoglobulin value
in mg/dL. It must be noted that in monoclonal gammopathies, that the
provided result for the monoclonal immunoglobulin is semi-quantitative.
Because these proteins are abnormal, an exact quantification cannot
be provided. In these situations, we use a combination of the RID
result with the electrophoresis to give an indication of the amount
of paraprotein.
It is important to know that there are different sources of these
RID kits. The immunoglobulin results cannot be compared between kits,
due to the use of different standards. Therefore, it is essential
to use the same laboratory for immunoglobulin measurement and to interpret
the results in relation to the laboratory's reference ranges. Comparing
the immunoglobulin results of the same animal from different laboratories
using different kits is invalid.
We currently offer immunoglobulin quantification in dogs, cats, horses,
cattle and llamas (for the latter , IgG only). We have established
our own reference intervals for dogs and cats, using RID kits from
Bethyl laboratories. These are valid for adult animals only (growing
animals usually have lower immunoglobulins and if a young animal is
being tested, several age-matched control animals should be submitted
concurrently). Our reference intervals for other species are provided
by the manufacturer and are age-dependent, therefore it is imperative
to provide an age when submitting these samples. |
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