Fig. 36-1 Neutrophils. Peripheral blood smear—chinchilla. These photographs show two mature (segmented) neutrophils, which contain faint acidophilic cytoplasmic granules. Compared with other mammalian species, neutrophils of chinchillas manifest a variation in segmentation; mature neutrophils frequently appear hyposegmented and can be misinterpreted as immature and erroneously classified as band or metamyelocyte forms. Moreover, automated analyzers may incorrectly identify these cells as being of mononuclear origin.

Fig. 36-2 Lymphocytes. Peripheral blood smear—chinchilla. These photographs show a reactive, or stimulated, lymphocyte (principal field) and two smaller mature lymphocytes (inset, lower right). Generally a stimulated lymphoid cell appears slightly enlarged compared with a nonreactive form and shows increased cytoplasm while maintaining a mature, densely compacted/condensed (smudged) nuclear chromatin pattern.

Fig. 36-3 Leukocytes. Peripheral blood smear—chinchilla. These photographs show a neutrophil (left) and an eosinophil (right, principal field) as well as a basophil (inset). Eosinophils generally contain prominent large pink- to orange-staining granules within clear to mildly basophilic cytoplasm. In most mammalian species, basophils tend to be the largest of the granulocytic cell types and reveal a blue-gray cytoplasm with variable numbers of darker-staining intracytoplasmic granules; these granules appear dark orange in this species, while in others they tend to be more basophilic, staining blue-black.

Fig. 36-4 Leukocytes. Peripheral blood smear—ferret. This field shows two mature segmented neutrophils in the upper right and left corners as well as a band form (lower right corner). Immature (band) neutrophils reveal less condensed nuclear chromatin patterns compared with mature neutrophils, without nuclear lobulation or segmentation; they generally show minimal constriction of the nuclear width. Note: Data derived from automated analyzers, including in-clinic instruments or those at large commercial reference laboratories, do not identify band neutrophils, instead relying on manual review by technicians or pathologists. Often these reviews are not performed if other CBC parameters (e.g., WBC/RBC) are within or near normal reference intervals. Bands are misidentified as either monocytes or segmented neutrophils by automated hematology analyzers.

Fig. 36-5 Leukocytes. Peripheral blood smear—ferret. These photographs show a monocyte (principal field) and a mature segmented neutrophil (inset). In ferrets and most other mammalian species, monocytes are larger than neutrophils and reveal variable nuclear size and shape, ranging from ameboid to multilobular. Monocyte cytoplasm appears blue-gray and grainy and may contain vacuoles. Large mononuclear cells are often distributed toward the feathered edges and sides of blood smears and may be underrepresented within the monolayered body of the smear during manual evaluation. Automated analyzers often incorrectly identify, or interchange, monocytes, neutrophils (particularly immature forms), and lymphocytes. Mature lymphocytes (not present) are generally smaller than neutrophils and reveal densely stained, compacted to smudged nuclear chromatin with scant, basophilic-staining cytoplasm.

Fig. 36-6 Platelet clumping. Peripheral blood smear—ferret. This field shows a large platelet clump (aggregation). The presence of large numbers of platelet clumps within a blood specimen may result in artifactually decreased platelet counts generated by automated methods, even if macroscopic clots are not observed. Moreover, clumps on a blood smear will falsely decrease manual platelet estimates. Platelets are oval to round, blue to gray, and may vary in size from one-fifth to greater than three-fourths the diameter of the RBCs. Larger platelets may be present in animals with increased platelet usage, such as that due to hemorrhage or exuberant systemic coagulation. In smears without platelet clumps, an acceptable method to estimate platelet numbers (per μL) using a 100× (oil-immersion) objective requires determining the average number of platelets in 10 microscopic fields (within the monolayer) and multiplying by 15,000.

Fig. 36-7 Leukocytes. Peripheral blood smear—guinea pig. These photographs show a basophil (principal field) and an eosinophil (inset). In this species, basophil granules generally stain reddish-purple, while eosinophils typically contain large spherical orange granules that together occupy much of the cytoplasmic space.

Fig. 36-8 Leukocytes. Peripheral blood smear—guinea pig. This field shows a neutrophil/heterophil (right) and a monocyte (left). The neutrophils of guinea pigs, hamsters, and gerbils are often referred as heterophils or pseudoeosinophils because they contain granules that stain eosinophilic in color with Romanowsky stains, as with the Wright’s-Giemsa method. Heterophils in these species perform similar functions as neutrophils; some clinicians interchange their names. In the guinea pig, eosinophils and heterophils are easily differentiated because of the size and number of the granules (see inset, Fig. 36-7); eosinophils have more numerous and larger round to rod-shaped granules. Eosinophils in many small mammal species often reveal a U-shaped nucleus. Automated hematology analyzers generally incorrectly identify heterophils/pseudoeosinophils as eosinophils.

(Modified Wright’s-Giemsa stain, 1000×.)

Fig. 36-9 Leukocytes. Peripheral blood smear—rabbit. These photographs show, from top to bottom (principal field), a monocyte (note intracytoplasmic vacuoles), a lymphocyte, a neutrophil/heterophil, and an eosinophil (inset). The neutrophils of rabbits are also referred to as heterophils because their cells do not stain neutral with Romanowsky stains. Note the more similar characteristics of eosinophils and heterophils in this species compared with guinea pigs.

Fig. 36-10 Lymphocytes with Kurloff’s bodies. Peripheral blood smear—guinea pig. These photographs (principal field and inset) show individual lymphocytes, each containing an intracytoplasmic Kurloff’s body, which is reddish-purple and often larger than the adjacent nuclei. Lymphocytes with Kurloff’s bodies (also known as Foa-Kurloff cells) are unique to this species and may account for 3% to 4% of the circulating leukocytes and occasionally more. These structures are found in higher proportions of circulating lymphocytes in young guinea pigs as well as in adult females. Lymphocytes containing Kurloff’s bodies are believed to be analogous to large granular lymphocytes, or natural killer (NK) cells, in other mammals.^2,19

(Modified Wright’s-Giemsa stain, 1000×.)

Fig. 36-11 Erythrocytes with Howell-Jolly bodies. Peripheral blood smear—mouse. This field shows several red cells containing intracytoplasmic Howell-Jolly bodies (arrows). These small dark-blue to black structures represent remnants of red cell nuclei and may be observed in low numbers within mature (anucleated) erythrocytes of healthy mammals. This photograph also reveals moderate polychromasia of the red cells. The proportion of red cells containing Howell-Jolly bodies may increase as a result of regenerative anemia or splenic dysfunction. Their presence should not be misinterpreted to suggest red cell parasites or Heinz bodies.

Fig. 36-12 Leukocytes. Peripheral blood smear—mouse. These photographs show two neutrophils and an eosinophil (principal field) and a monocyte (inset) as well as scattered polychromatic red cells. Mature neutrophils of rats and mice generally have a clear-staining cytoplasm, but they may contain a few dust-like reddish granules and appear diffusely pink with Romanowsky-type stains. Granulocytes of rodents often have nonlobulated nuclei; these may be horseshoe- or ring-shaped. Rodent eosinophils show considerably fewer and less distinct granules than those of other small mammals. In rats and mice, an age-dependent variation exists in the neutrophil:lymphocyte (N:L) ratio, with the lymphocyte concentration decreasing and the neutrophil concentration increasing as the animal ages.^4,19 In rodents, automated analyzers often incorrectly identify a variable proportion of neutrophils and/or lymphocytes as monocytes.

(Modified Wright’s-Giemsa stain, 1000×.)

Fig. 36-13 Erythrocyte polychromasia and reticulocytes. Peripheral blood smear—rabbit. These photographs show several polychromatic red cells (arrows) stained with a modified Wright’s-Giemsa stain (principal field) and aggregate reticulocytes stained with new methylene blue stain (inset). Polychromasia, a bluish-gray coloration, is caused by higher quantities of ribosomal RNA present in immature, anucleated red cells. Compared with the red cell life span in other mammals, the relatively shorter half-life of rabbit erythrocytes (57-67 days) results in a higher proportion of polychromatic erythrocytes and reticulocytes. Reticulocytes in adult rodents, rabbits, and hystricomorphs (guinea pigs and chinchillas) range between 2% to 7%. Reticulocyte staining requires a 15-minute incubation of any volume of whole fresh blood with an equal quantity of new methylene blue (0.5% in saline). Smears are then prepared and allowed to air-dry prior to examination. (1000×.)