Our “Consider This Case” series presents diagnostic challenges. Microscopic examination of a blood smear that has been well prepared is crucial to veterinary diagnostic hematology and is critical to patient care.
Two main reasons highlight the importance of blood films:
- To verify in-clinic analyzer results
- To identify critical diagnostic features that these analyzers cannot evaluate.
Review the following case reports and then see if you can correctly answer the questions posed based on the complete blood count (CBC) results and blood film images provided. Answers are presented at the end of this article
Case Report 1:
German Shepherd with Recurrent Skin Infections & Exercise Intolerance
A 9-year-old intact male German shepherd presents with a history of recurrent skin infections and exercise intolerance. Physical examination reveals bilateral epiphora, ventral alopecia, and areas of skin lichenification. Pre-anesthetic CBC is completed prior to skin biopsies. Table 1 outlines the significant results from the hematology analyzer, while Figure 1 represents the high magnification field from the microscopic evaluation of this patient’s blood film.
Consider This Question… Identify the nucleated cells: is the leukocyte count correct?
FIGURE 1. Case Report 1: Representative image from the counting area of the blood film. Wright-Giemsa stain; magnification, 1000×.
Diagnostically essential morphologic abnormalities can be present even in patients with quantitatively normal results for all hematologic parameters.
Case Report 2:
Australian Shepherd with an Oral Mass
A 9-year-old castrated male Australian shepherd presents for evaluation of an oral mass. A pre-anesthetic CBC is completed (Table 2) and a dental examination under general anesthesia is scheduled. Figure 2 represents the high magnification field from the microscopic evaluation of this patient’s blood film.
Consider This Question… Identify the nucleated cells: does this patient have a left shift indicative of underlying inflammation?
FIGURE 2. Case Report 2: Representative image from the counting area of the blood film; note the presence of debris (arrow) that is likely stain precipitate, which may be confused with the presence of organisms. Wright-Giemsa stain; magnification, 1000×.
Case Report 3:
English Toy Spaniel with Head Tilt, Rotary Nystagmus, & Ataxia
A 3-year-old castrated male English toy spaniel presents with clinical signs of vestibular disease—head tilt, rotary nystagmus, and ataxia. No other physical examination abnormalities are noted. Table 3 provides the results from a CBC; plateletcrit is within reference intervals. Figure 3 represents the high magnification field from the microscopic evaluation.
Consider This Question… Characterize the morphology of the platelets: is this patient at risk of bleeding?
CBC = complete blood count; WNL = within normal limits
FIGURE 3. Case Report 3: Representative image from the counting area of the blood film. Wright-Giemsa stain; magnification, 1000×.
Case Report 1: Answer
The presence of nucleated red blood cells is causing an erroneously elevated total white blood cell count by the hematology analyzer (Table 1); Table 4 provides a corrected CBC. Without blood film review, this patient would be erroneously diagnosed with an inflammatory leukogram, with the significant numbers of metarubricytes unidentified because they were interpreted as leukocytes by the analyzer.
Ultimately, the cause of the metarubricytosis and nonregenerative anemia could not be identified, but the patient responded to immunosuppression, with resolution of both anemia and metarubricytosis.
Case Report 2: Answer
A neutrophil (arrow) and eosinophil (arrowhead) are characterized by Pelger-Huët anomaly, a heritable disorder that results in hyposegmentation of granulocytes. The absence of toxic change helps distinguish this anomaly from a left shift associated with an inflammatory leukogram. Pelger-Huët anomaly is common in Australian shepherds. Note that the quantitative data are not impacted by this change, which is not detected by automated analyzers.
Case Report 3: Answer
Two macroplatelets (arrows) are approximately the same size as erythrocytes. English toy spaniels are a breed affected by congenital macrothrombocytopenia, which is not associated with hemostatic abnormalities. Therefore, in breeds predisposed to congenital macrothrombocytopenia, this diagnosis should be considered in asymptomatic dogs with persistent macrothrombocytopenia.
Congenital macrothrombocytopenia must be distinguished from immune-mediated thrombocytopenia by repeated hematologic evaluation, monitoring for clinical signs, and/or genetic testing. In this patient, artifactual thrombocytopenia was excluded by evaluation of the tube and blood film for evidence of platelet clumping.
An MRI was completed and revealed no abnormalities leading to a final diagnosis of idiopathic vestibular ataxia.
CBC = complete blood count; RBC = red blood cell; WBC = white blood cell; WNL = within normal limits