Lecture 14/15 - Measurement and interpretation of the leukogram

What is the white blood cell concentration?

Measurement of nucleated cells per volume of blood

How can WBC be calculated?

-Manual count (hemocytometer)

-Automated count

-Estimated from blood smear

What are the common sources of error with an automated WBC?

-Leukocyte clumping

-Leukocyte lysis (usually due to age)

-Large or clumped platelets

-Cellular debris

-nRBCs

Why would a blood smear be used to determine WBC?

-Verifies accuracy of automated count

-WBC = (average WBC)(objective power²)

How is the absolute cell count calculated?

Multiply differential count (in %) by WBC

Which is more important when looking at a manual WBC: absolute cell counts or relative percentages?

Absolute cell counts

What is a leukocytosis?

Increased WBC

What is a leukopenia?

Decreased WBC

What is a neutrophilia

Increased absolute neutrophil count

What is a neutropenia

Decreased absolute neutrophil count

What is a left shift

Presence of immature neutrophils (usually bands)

What is a lymphocytosis

Increased absolute lymphocyte count

What is a lymphopenia

Decreased absolute lymphocyte count

What is a monocytosis

Increase in absolute monocyte count

What is a monocytopenia

Decrease in absolute monocyte count

What is a eosinophilia/basophilia

Increase in absolute eosinophil/basophil count

What is a eosinopenia/basopenia

Decrease in absolute eosinophil/basophil count

What are 6 common leukogram patterns that may be observed?

1. Stress (glucocorticoid)

2. Adrenaline/excitement

3. Antigenic stimulation

4. Inflammation

5. Granulocytic hypoplasia

6. Neoplasia (leukemia)

Which leukogram pattern is commonly found in clinically ill animals?

Stress leukogram

What is the cause of a stress leukogram?

-Glucocorticoids (cortisol-mediated shifts)

-Chronic and sustained stress

When is something considered moderate vs mild?

Moderate if levels are 2x or higher/lower than upper reference level

What are the common changes in WBC types that you will see with a stress leukogram? Which one is the number one sign?

-Mild to moderate leukocytosis

-Neutrophilia (shift from marginating to circulating pool)

-Lymphopenia - #1 sign

-± monocytosis (mild)

-± eosinopenia 

What is the cause of an adrenaline/excitement leukogram?

-Epinephrine mediated shifts

-Immediate

What are the common changes in WBC cells that you will see with an adrenaline/excitement leukogram?

-Leukocytosis (mild to moderate)

-Neutrophilia (rapid shift from marginating to circulating)

-Lymphocytosis (splenic contraction)

-± Monocytosis

What species are excitement leukograms most common in?

Cats and young horses

What is the cause of an antigenic stimulation in a leukogram?

Chronic immune stimulation or cytokine production

What are the general features of acute inflammation?

-Neutrophilia

-Left shift

-Toxic change to neutrophils

-± Monocytosis (same pregenitor cell as neutrophils/increased macrophage demand)

What occurs with overwhelming/uncompensated acute inflammation?

Neutropenia with a left shift

What are the key features of severe inflammation with WBCs?

-Neutrophilia (>50-100K/uL)

-Leukemoid response

What are the causes of severe inflammation causing a neutrophilia?

-Pancreatitis

-Peritonitis

-Pneumonia

-IMHA

-Other causes of severe localized/systemic inflammation

What is the leukemoid response? What do you need to check?

-Strong leukocytosis that needs to be differentiated from neoplasia

-Check blood smear for blast cells/other neoplastic chages

What is a regenerative left shift? What is the key sign?

-Bone marrow is responding appropriately

-Segmented neutrophils outnumbers bands

What is a degenerative left shift? What is the key sign?

-Bone marrow is overwhelmed by inflammatory response

-Band neutrophils outnumber segmented neutrophils OR left shift with a neutropenia

What is the species difference with acute inflammation?

Cattle have small neutrophil storage - usually manifests as neutropenia in early stages followed by rebound neutrophilia

What WBC changes are common with chronic inflammation?

-Rebound neutrophilia ± left shift

-± monocytosis (same progenitor cells)

How can you diagnose chronic inflammation?

Need serial data - may look similar to acute inflammation with no other information

How long does the rebound response generally take?

3-5 days

What is granulocytic hypoplasia?

Decreased bone marrow production of neutrophils

What are some causes of granulocytic hypoplasia?

-Immune-mediated destruction

-Chemotherapy/drugs/toxins

-Bone marrow diseases

-Cyclic neutropenia (grey collies)

What WBC findings will you see with granulocytic hypoplasia?

Persistent and progressive neutropenia with NO left shift

What is acute leukemia? What is the outcome?

-Neoplastic transformation of hematopoietic precursors

-Rapid clinical course with poor prognosis

What are the key signs of acute leukemia?

-Immature/blast cells with prominent nucleoli

-Mitotic capability

-Marked leukocytosis (>50-100k)

What is chronic leukemia? What are the common signs? Which cell type is most commonly involved?

-Disease of accumulation - mutations over time allow for prolonged survival and avoidance of apoptosis

-Usually will see no overt clinical signs

-Usually lymphoid but can be any leukocyte

What is the difference between acute and chronic leukemia?

Acute involves immature cell types while chronic involves mature cell types

What are the common causes of an eosinophilia?

-Parasitic (usually GI parasites)

-Hypersensitivity responses

-Paraneoplastic diseases (IL-5 producing tumors)

What is the clinical significance of an eosinopenia?

-Not clinically significant

-May be a component of stress leukogram

What cell type is this? What species is it commonly found in?

-Heterophils

-Found in rabbits, guinea pigs, gerbils, elephants, etc

What are heterophils?

-Functionally equivalent to neutrophils

-Contain rod-shaped pink cytoplasmic granules (do not confuse with eosinophils)

What cell type is this? What species is it found in?

-Foa-Kurloff cells

-Found in guinea pigs and capybaras

What are species differences with WBC in birds and reptiles?

-Heterophils

-Azurophils (reptiles)

-Nucleated RBCs

-Nucleated thrombocytes

-Leukocyte morphology is highly variable between species