Canine bone marrow processing choices may shape IHC results

CURRENT FULL VERSION: A new Veterinary Pathology paper focuses on a familiar but under-discussed problem in veterinary diagnostics: what happens to canine bone marrow samples before they ever reach the microscope. Because marrow cores include both soft hematopoietic tissue and mineralized bone, they must be fixed and demineralized before sectioning. The new study asks how those steps affect immunohistochemical assessment, a practical question for pathologists working up marrow disease, lymphoma involvement, leukemia, mast cell disease, and other cases where morphology alone may not be enough. (pmc.ncbi.nlm.nih.gov)

The work comes out of a broader effort by investigators at the University of Guelph, with collaboration from UC Davis, to standardize canine bone marrow processing. In an associated study published from the same project, the group tested two fixatives, acid-zinc-formalin and 10% neutral-buffered formalin, along with three demineralization approaches: EDTA, formic acid, and hydrochloric acid. They found that fixative choice had little effect on basic histomorphology, but demineralization choice mattered a great deal. EDTA preserved marrow architecture best, while acid-based methods caused more trabecular fragmentation and poorer osteocyte preservation. (pmc.ncbi.nlm.nih.gov)

That earlier paper also showed why preanalytic handling matters beyond slide appearance. DNA amplification succeeded in 29 of 36 EDTA-treated samples, versus just 2 of 72 samples decalcified with hydrochloric or formic acid. When the authors modeled the data, samples fixed in neutral-buffered formalin were more likely than acid-zinc-formalin samples to yield amplifiable DNA, but the strongest signal was still the decalcifier: EDTA dramatically outperformed acid methods. The authors concluded that marrow tissue likely to need PCR-based follow-up should be decalcified with EDTA rather than acids. (pmc.ncbi.nlm.nih.gov)

That molecular preservation point is consistent with findings outside marrow pathology as well. In a separate Animals paper on mineralized cervid tissues, researchers developed a simple EDTA-based digestion and organic-solvent extraction workflow for deer antlers and prepared trophy skulls that avoided commercial kits and cryogenic grinding. Using bead-based homogenization, a 4-hour enzymatic digestion in EDTA buffer with N-lauryl sarcosine and Proteinase K, followed by phenol-chloroform-isoamyl alcohol purification and centrifugal filtration, they generated DNA suitable for downstream testing from 60 samples spanning roe deer, fallow deer, and red deer. Multiplex PCR of species-specific microsatellite markers produced complete genotypes from all 60 samples. That study was not about canine marrow or histology, but it reinforces the broader practical lesson that EDTA-based processing can preserve useful DNA even in challenging mineralized tissues when molecular analysis is the goal.

That background is important for interpreting the new immunohistochemistry-focused report. In the histomorphology and DNA paper, the authors explicitly said the effect of fixation and decalcification on IHC still needed to be evaluated. They had initially hypothesized that acid-zinc-formalin might better preserve antigens, based on prior work in other species, but their own canine marrow data did not show a morphology advantage over neutral-buffered formalin. In other words, the question of antigen preservation in canine marrow was still open, and this new study is aimed squarely at that gap. (pmc.ncbi.nlm.nih.gov)

Industry and laboratory context points in the same direction: standardization is overdue. The University of Guelph’s Animal Health Laboratory offers immunohistochemistry services and companion animal histopathology workflows that include demineralization for bone and other hard tissues, underscoring that these are real-world operational choices, not just academic variables. More broadly, bone marrow pathology guidance in human medicine has long warned that acid decalcification can undermine IHC and molecular assays unless labs validate protocols carefully, and published oncology pathology data show EDTA can preserve key biomarker readouts better than hydrochloric- or formic-acid approaches. That doesn’t make human data directly transferable to dogs, but it does support the study’s practical relevance. (uoguelph.ca)

Why it matters: For veterinary professionals, especially diagnostic pathologists, oncologists, and internists submitting marrow cores, this is a reminder that specimen handling can shape the final diagnosis. Faster acid decalcifiers may help turnaround time, but if they reduce antigen detectability or limit ancillary testing, the apparent efficiency can come at the cost of diagnostic confidence. In cases where pet parents and clinicians are trying to distinguish reactive marrow from infiltrative neoplasia, classify hematopoietic disease, or preserve material for clonality or molecular assays, a more conservative EDTA-based workflow may offer better long-term value. The tradeoff is time: in the related study, hydrochloric acid worked in about 1 hour, formic acid overnight, and EDTA about 24 hours, with fresh EDTA replacement after 12 hours. (pmc.ncbi.nlm.nih.gov)

The bigger implication is that veterinary labs may need to think less in terms of a single “best” marrow protocol and more in terms of intended downstream use. If a sample is only needed for routine morphology, one workflow may suffice. If IHC, PCR, or future molecular profiling is likely, preanalytic choices should be made with those endpoints in mind. The deer antler and trophy-skull study adds a useful parallel here: even heavily mineralized tissues can yield high-quality DNA for complete genotyping when EDTA-based processing is built into the workflow from the start. That’s particularly relevant as veterinary oncology and hematopathology continue moving toward more layered diagnostics. (pmc.ncbi.nlm.nih.gov)

What to watch: The next step is validation at the marker level, including which canine marrow antigens hold up best under different fixation and demineralization conditions, and whether veterinary diagnostic labs revise standard operating procedures as those data emerge. (pmc.ncbi.nlm.nih.gov)