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Flags for Review of CBCs

WBC flags:

  • Pancytopenia
  • Degenerative left shift with no toxic change or if questioning cell identification
  • Toxic change with no left shift
  • Left shift (>1% bands) with no toxic change in a horse or cow.
  • WBC > 30,000 in large animals
  • WBC > 50,000 in small animals
  • Histiocytes
  • Mast cells – any in a cat, >3 in a dog
    • If you see <3 mast cells in a dog add a comment saying: A few (or a single) mast cells see in feather.
  • Absolute lymphocytosis in an animal >2yrs
    • If you see an increase in lymphocytes on your differential check the WBC count, if the WBC count is low the lymphocytosis may be relative (i.e. neutropenia and normal lymphocyte count). A quick way to assess whether an increase lymphocyte % will also be an absolute lymphocytosis is to look at the Advia absolute lymphocyte count – it will be close to the count on the final report if the Advia differential is similar to your manual differential.
    • If there is an absolute lymphocytosis and the animal is less than 2yrs old, and the lymphocytes are small mature forms, there is no need to send for review since it is likely an epinephrine response.
    • If the animal is over 2 yrs or there are any atypical lymphocytes seen, then send it for review.

Blasts or other atypical cells:

  • Blasts: round cells with fine chromatin with or without nucleoli.
  • Other leukocytes with abnormal morphology which may include:
    • Abnormal granulation or inclusions
    • Large cells – e.g. giant neutrophils


Notes on reactive lymphocytes/granular lymphocytes:

  • Typical reactive lymphocytes are often intermediate or large with clumped chromatin and deep blue cytoplasm.
  • Reactive lymphocytes on the smear generally appear heterogenous – i.e. varying sizes, nuclear shapes etc.
  • Lymphocytes which are small with mature chromatin but have increased amounts of light blue cytoplasm are generally not considered reactive or abnormal unless there is a lymphocytosis or if they predominate the lymphocytes.
  • Healthy animals can have up to 10% granular lymphocytes, however, lymphocytes with very large granules or large lymphocytes with granules should be flagged and the CBC reviewed.

Very low neutrophil count – always look carefully for toxic change and left shift. 

Toxic change only in bands

  • whether to call toxic or not depends on the severity of the toxic change
  • do not call toxic if only in a few bands and mild toxic change
  • call mildly toxic if moderate to severe toxic change in bands only

RBC flags:

  • Anemia with Hct ≤ 15, or ≤ 20 in the horse and dog
  • Any nucleated RBCs in a horse
  • Large numbers (>20) of nucleated RBCs in other species in the absence of regeneration
  • Hypochromasia
  • Macrocytes in anemic horses
  • Spherocytes – should be reviewed on first presentation or if getting worse
  • Agglutination – same as above
  • Parasites other than leukocytozoon, microfilaria and straightforward hemoproteus (halter shape, if smaller and round slide should be reviewed since it could be plasmodium)
  • Ovalocytes in a dog
  • Moderate to many siderocytes or very prominent siderocytes
  • Heinz bodies in any species but a cat
  • Large Heinz bodies in a cat


  • Very low platelets - <50,000 when the count is not matching the smear, you should see an average of 3/1000X field if count is 50,000.
  • Any time the counts are not matching the smear.

Coombs test:

  • Review a blood smear and do a CBCA on all Coombs tests. Review all positive Coombs if not a classic IMHA (i.e. regenerative anemia, spherocytes).