Evaluation of Leukocytosis:

The term 'leukocyte' applies to any cells within the myeloblast, monoblast, & lymphoid lineages.

Include granulocytes (neutrophils, eosinophils, & basophils), monocytes, & lymphocytes (B cells, T cells, and natural killer cells).

In adults, leukocytosis often defined as white blood cell (WBC) count > 11 × 109/L.



Mature WBC:

80-90% remain in storage in bone marrow.

2% to 3% circulate freely in peripheral blood;

The rest stay deposited along the margins of blood vessel walls or in the spleen

Life span: 2- 16 days (depending on cell type in the peripheral circulation).



LEUCOCYTOSIS

WBC > 11,000 per mm3 [11.0 × 109 per L]

Reactive: Typically, 11,000 to 30,000 per mm3.

Leukemoid reaction: approx. 50,000-100,000 per

(e.g., C difficile infection, sepsis, organ rejection, or solid tumors.

Leukemias or myeloproliferative disorders: > 100,000 per mm3.



Paradoxical neutropenia: typhoid fever, rickettsia infections, brucellosis, & dengue.



Neutrophil bands:

Immature neutrophils

Morphologically: absence of complete separation of nuclear lobes with a visible distinction between chromatin & parachromatin in the narrowest segment of the nucleus often flagged on 5-part automated differential & confirmed by PBS.



Leukemoid Reaction: 

Transient increase in WBC count defined as significant neutrophilia >50x10^9/L in the absence of a myeloproliferative neoplasm. 

Mature neutrophils seen in a leukemoid reaction.

Etiology: sepsis, organ rejection, solid tumors, and bacterial infections. 

D/D leukemia: increases in blast cells (precursor cells to leukocytes) and immature WBCs,  

Improves after treating the underlying cause.



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