Figure 12: In this blood film, a few platelet clumps are present, but the platelets trapped within the clumps are not counted by the hematology analyzer.
DIC = disseminated intravascular coagulation; nRBC = nucleated red blood cell; WBC = white blood cell
This correction will also adjust inaccurately elevated absolute counts of each leukocyte type in the leukocyte differential. In addition to the nRBCs, the dog also had other findings consistent with a regenerative anemia, including polychromasia and anisocytosis.
Microfilariae. Numerous microfilariae, which cannot be detected by hematology analyzers, were observed on the blood film and suggested the cause of the dog’s congestive heart failure. Subsequent echocardiography revealed caval syndrome, a condition where a mass of worms in the right heart disrupts normal blood flow and can cause fragmentation hemolysis, which can, in turn, incite disseminated intravascular coagulation (DIC). The few schistocytes observed in the blood film indicated mild fragmentation hemolysis. Schistocytes found in tandem with anemia and confirmed thrombocytopenia also indicated development of DIC.
Did you answer…
- The erythrocytes show increased polychromasia and anisocytosis, and there are some nRBCs and schistocytes. The neutrophils are 2+ to 3+ toxic and left-shifted, with many band neutrophils in circulation.
- nRBCs are counted with other nucleated cells by hematology analyzers and included in the total leukocyte count, causing a falsely increased total leukocyte count if there are > 5 nRBCs/100 WBCs. Band neutrophils and further left-shifted neutrophils are usually counted as mature, segmented neutrophils by hematology analyzers.
- The number of platelets in the blood film is reduced, consistent with the thrombocytopenia reported by the hematology analyzer. Concurrent thrombocytopenia, anemia, and poikilocytosis due to schistocytes raise concern for possible underlying DIC.
- Circulating microfilariae suggest heartworm infection, which is likely related to this patient’s congestive heart failure.
Case 3: Prior History of Leukemia & Chemotherapy
Diagnosis: Acute lymphocytic leukemia (no longer in remission) with Babesia canis infection unmasked by immunosuppressive chemotherapy
Interpretation & Discussion
Although the total leukocyte count was within the reference interval, evaluation of leukocyte morphology in the blood film revealed that abnormal leukocytes, specifically large lymphoblasts, were the predominant cell type (Table 3). Once the blasts were included in the manual leukocyte differential as a separate category, the absolute counts of the other leukocyte types decreased.
Erythrocyte morphology was also abnormal. There were numerous intraerythrocytic piroplasms consistent with Babesia canis, which cannot be detected by hematology analyzers (Figure 13). In this case, the blood film contained important additional information that only a trained microscopist could discern during evaluation.