WBC Morphology

White Cell Differential Count

A manual WBC differential count is performed by having a person trained in peripheral blood morphology review the stained blood smear and manually count 100 white cells (or 50 cells in the case of severe leukopenia). The major advantage is that the observer can determine subtle differences in morphology and observe additional changes in RBC morphology and platelets. The major disadvantage is the need for a trained person to spend increased time (with increased cost) needed to scan the smears. Also, there can be some inter-observer variation.

A standard complete blood count is performed on an automated laboratory instrument that quantitates the number of WBC's present. Some instruments are also able to perform an "automated" WBC count. The advantages of the automated WBC differential are speed, low cost per test, and the precision from the large number of cells counted. The disadvantages include the initial cost of buying the instrument, inability to distinguish subtle differences in morphology, more marked abnormalities, and lack of information about RBC's or platelets.

An example of a CBC with automated WBC differential count is shown below. The absolute numbers for total WBC count and each type of leukocyte are in thousands per cubic millimeter (or alternatively, per microliter).

The absolute white blood cell counts are most useful, and are calculated by multiplying the % of each cell type counted by the total WBC count. Simple percentages may be misleading, since an apparent percentage increase in one constituent may actually be due to a significant and absolute decrease of another type of WBC. For example, 99% lymphs with an absolute WBC count of 1300/microliter means neutropenia, not lymphocytosis. Always consider the WBC percentages in the context of the total WBC count.

Nomenclature

The following terms are used in describing the morphology of WBC's, as seen on a standard peripheral blood smear:

Neutrophilia

An increase in the absolute neutrophil count, it can be increased transiently with stress and exercise by a shift of neutrophils from the marginating pool to the circulating pool. Pathologic processes that result in neutrophilia include:

Infection

Toxins: metabolic (uremia), drugs, chemicals

Tissue destruction or necrosis: infarction, burns, neoplasia, etc

Hemorrhage, especially into a body cavity

Rapid hemolysis

Hematologic disorders: leukemias, myeloproliferative disorders

Neutropenia

A decrease in the absolute neutrophil count. Pathologic processes that result in neutropenia include processes that decrease production or increase destruction. Diseases that decrease neutrophil production include:

Aplastic anemia

Toxins that damage marrow

Collagen vascular diseases (such as SLE)

Myelphthisic marrow processes such as marrow infiltration by infections or metastatic carcinomas

Hematologic malignancies such as leukemias

Myeloproliferative disorders

Radiation therapy

Chemotherapy

Congenital disorders

Diseases that increase neutrophil destruction include:

Splenomegaly with hypersplenism

Infection

Immune destruction

Lymphocytosis

An increase in the number of circulating lymphocytes may normally be observed in infants and young children. Pathologic processes with lymphocytosis may include:

Acute infections, including pertussis, typhoid, and paratyphoid

Infectious mononucleosis, with "atypical" lymphocytosis

Viral infections, including measles, mumps, adenovirus, enterovirus, and Coxsackie virus

Toxoplasmosis

HTLV I

Lymphopenia

A decrease in the number of circulating monocytes may be seen with:

Immunodeficiency syndromes, including congenital (DiGeorge syndrome, etc) and acquired (AIDS) conditions

Corticosteroid therapy

Neoplasia, including Hodgkin's disease, non-Hodgkin's lymphomas, and advanced carcinomas

Radiation therapy

Chemotherapy

Monocytosis

An increase in the number of circulating monocytes may be seen with:

Infections: such as brucellosis, tuberculosis and rickettsia

Myeloproliferative disorders

Hodgkin's disease

Gastrointestinal disorders, including inflammatory bowel diseases and sprue

Monocytopenia

A decrease in the number of circulating monocytes may be seen with:

Early corticosteroid therapy

Hairy cell leukemia

Eosinophilia

An absolute increase in the number of circulating eosinophils may occur with:

Allergic drug reactions

Parasitic infestations, especially those with tissue invasion

Extrinsic asthma

Hay fever

Extrinsic allergic alveolitis ("farmer's lung"

Chronic infections

Hematologic malignancies: CML, Hodgkin's disease

Eosinopenia

An absolute decrease in the number of circulating eosinophils may occur with:

Acute stress reactions with increased glucocorticoid and epinephrine secretion

Acute inflammation

Cushing's syndrome with corticosteroid therapy

Basophilia and Basopenia

An absolute increase in the number of circulating basophils may occur with myeloproliferative disorders and with some allergic reactions.

An absolute decrease in the number of circulating basophils may occur with the same conditions that lead to eosinopenia.

Morphologic Findings

The following terms are used in describing the morphologic variation seen in WBC's on a standard peripheral blood smear:

WBC Morphology Diagrams

Morphologic appearances of WBC's on a peripheral blood smear include the findings pictured below. Moving the mouse over each image will reveal the name in the status bar at the bottom.