First, examine the blood film at low magnification (10× or 20×), and scan the entire slide to evaluate overall film thickness,
cell distribution, and differentiation of the three different zones. Evaluate the feathered edge (Figure 3) for microfilariae, phagocytized organisms, atypical cells, and platelet clumping. Next, examine the body of the blood film
(Figure 4) for rouleau formation or RBC agglutination. Then, still using low magnification, evaluate the monolayer (Figure 5), estimate the total WBC count (see the third article in this symposium), and predict the expected WBC differential count. Finally, use the oil-immersion objective (100×) to examine RBC, WBC, and
platelet morphology in the monolayer.
Figure 3. Look for platelet clumps, microfilariae, and large cells in the feathered edge of the film (purple section).
Evaluate RBCs for evidence of anisocytosis, poikilocytosis, polychromasia, hemoglobin concentration, and RBC parasites. Important
RBC morphologic abnormalities include spherocytes, schistocytes, acanthocytes, and leptocytes (see the second article in this symposium).
Figure 4. Look for rouleau formation and RBC agglutination in the body of the film (purple section).
Evaluate neutrophils for toxicity and the presence or absence of a left shift (increased numbers of band neutrophils). Evaluate
lymphocytes for reactivity and monocytes for phagocytized organisms (see the third article in this symposium).
Figure 5. Estimate platelet and WBC counts and examine cell morphology in the monolayer zone (purple section).
With relatively little practice, you can identify most important morphologic abnormalities in the RBCs, WBCs, and platelets
with the 20× objective field of view; these can be quickly validated with the 100× oil-immersion view.
Examining a properly prepared peripheral blood film offers invaluable information about cellular morphologic changes not provided
by automated instruments and provides a quality assurance confirmation of CBC data generated by in-clinic or reference laboratory
hematology analyzers. We recommend taking about three minutes to view the blood film and, using the questions discussed in
the next two articles of this symposium, to systematically evaluate the RBC, platelet, and WBC components of the peripheral
Fred L. Metzger Jr., DVM, DABVP (canine and feline practice)
Metzger Animal Hospital
1044 Benner Pike
State College, PA 16801
Alan Rebar, DVM, PhD, DACVP
Department of Veterinary Pathobiology
School of Veterinary Medicine
West Lafayette, IN 47907
The authors gratefully acknowledge the technical assistance and images provided by Dennis DeNicola, DVM, PhD, DACVP.
1. Willard, M. et al.: The complete blood count and bone marrow examination. Textbook of Small Animal Clinical Diagnosis by Laboratory Methods, 3rd Ed. W.B. Saunders, Philadelphia, Pa., 1999; pp 11-30.
2. Rebar, A.; Metzger, F.: The Veterinary CE Advisor: Interpreting Hemograms in Cats and Dogs. Vet. Med. (suppl.) 96 (12):1-12; 2001.