Comparison of the bone marrow composition in samples from rib, ilium, sternum, and humerus of dogs

Bone marrow (BM) samples in dogs are typically acquired from hematopoietically active trabecular BM at appendicular skeletal sites, such as the proximal humerus and femur, or axial skeletal sites, such as pelvis, sternum, and rib. Suitability for in vivo biopsy varies by site, but equivalency of BM composition at different sites is uncertain. We sought to determine whether the composition of BM is comparable in humerus, ilium, rib, and sternum. Samples from each site were obtained within 24 h after death from 30 dogs with spontaneous disease submitted for postmortem examination. Tissues were fixed in acetic acid-zinc-formalin, demineralized with EDTA, and assessed by 4 independent raters for hematopoietic cellularity, granulocytic:erythrocytic (G:E) cell ratio, megakaryocyte (MKC) number, and presence of hemosiderin. Statistical analysis showed lower cellularity, MKC number, and hemosiderin in ilium than in rib, higher cellularity in rib and sternum than in humerus and ilium, and lower G:E cell ratio in rib than in humerus (p < 0.05). Analysis of covariance indicated that most differences between sites were attributable to individual animal variation rather than site or rater. Differences overall were of small magnitude, and values for each parameter were similar to those reported in healthy younger dogs. We concluded that samples from any of the 4 sites are suitable to approximate composition of BM at the other sites.