PARR stands for PCR for Antigen Receptor Rearrangements. This is a clonality assay that helps to distinguish neoplastic from inflammatory lymphoid cells. Lymphoid neoplasms are monoclonal expansions of malignant lymphoid cells, whereas inflammatory lymphoid cells are usually polyclonal. Depending on animal species, the tests are based on single or multiple uniplex or multiplex PCRs for T cells and B cells, targeting the CDR3 region of T-cell receptor gamma and immunoglobulin heavy chain genes, respectively. PCR primers target conserved regions flanking the hypervariable regions of these genes.

There are numerous indications for using PARR in canine or feline lymphoid diseases, especially when the morphological, cytological, or immunophenotypic properties of a lymphoid cell population are inconclusive. For example, PARR is useful to differentiate follicular lymphomas such as T-zone lymphoma or marginal zone lymphoma from hyperplastic reactions when there is lack of architectural effacement.

PARR can also be used to characterize lymphohistiocytic proliferations in the feline or canine skin and is a major component of the diagnostic algorithm to differentiate feline inflammatory bowel disease from intestinal lymphoma. For feline intestinal biopsies, a specific panel is available.

At the MSU VDL laboratory we perform triplicate amplification, heteroduplex analysis, and capillary electrophoresis on a regular basis for diagnostic cases, which allows us to achieve the highest possible sensitivity as well as avoid pseudoclones, which are false positive results. PARR results should never be interpreted independent of morphology. We therefore only offer PARR in combination with a biopsy or a second opinion and immunophenotyping which include additional charges.

All tests can be performed on routine formalin-fixed biopsy material as well as previously submitted biopsy samples. Alternatively, clients can request another pathology service to submit the paraffin block if the tissue was originally processed elsewhere. For more information, including pricing, please see our catalog of available tests or call the lab at 517.353.1683.