Measurement of individual immunoglobulins is performed for 2 reasons:
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.
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 It has been replaced by immunoglobulin quantification by single radial immunodiffusion (RID), which we use here at Cornell University.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 VMRD or Triple J Farms. 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.