Benign disorders of white blood cells

Quantitative leukocyte disorders

Abnormal changes in leukocyte numbers (leukocytosis or leukopenia)

Qualitative leukocyte disorders

Abnormal changes in leukocyte morphology or function

Relative count

Percentage of a leukocyte type in the differential count

Absolute count

Actual number of a leukocyte type in blood

Absolute count formula

Total WBC count × percentage of specific leukocyte type

Three major functions of neutrophils and monocytes

Chemotaxis, phagocytosis, killing and digestion

Chemotaxis

Directed migration of leukocytes toward infection

Phagocytosis

Engulfment of microorganisms by leukocytes

Defective chemotaxis causes

Lazy leukocyte syndrome, corticosteroids, leukemia, MDS

Defective phagocytosis causes

Hypogammaglobulinemia and complement deficiency

Chronic granulomatous disease

Defective intracellular killing due to impaired respiratory burst

Myeloperoxidase deficiency

Defective microbial killing due to lack of MPO enzyme

Pelger-Huët anomaly

Autosomal dominant disorder with bilobed neutrophils

Characteristic appearance of Pelger-Huët neutrophils

Pince-nez (spectacle-shaped) nuclei

May-Hegglin anomaly

Basophilic inclusions in neutrophils with giant platelets and mild thrombocytopenia

Chediak-Higashi syndrome

Autosomal recessive disorder with giant granules in leukocytes

Peripheral blood finding in Chediak-Higashi syndrome

Giant cytoplasmic granules in neutrophils

Hypersegmented neutrophils are classically seen in

Megaloblastic anemia

Toxic granulation indicates

Severe bacterial infection or inflammation

Dohle bodies

Blue-gray cytoplasmic inclusions seen during infection and inflammation

Pelger-like cells in acquired disease

Associated with myelodysplasia and myeloid leukemia

Neutrophilia definition

Absolute neutrophil count >7.5 × 10⁹/L

Left shift

Increased immature neutrophils in peripheral blood

Peripheral blood findings in reactive neutrophilia

Left shift, bands, toxic granulation, Dohle bodies, high NAP score

Most common cause of neutrophilia

Acute bacterial infection

Important non-infectious causes of neutrophilia

Trauma, infarction, hemorrhage, hemolysis, corticosteroids

Leukemoid reaction

Exaggerated reactive leukocytosis with immature granulocytes

Causes of leukemoid reaction

Severe infection, severe hemolysis, metastatic cancer

Best test to distinguish leukemoid reaction from CML

NAP/LAP score

NAP/LAP score in leukemoid reaction

High

NAP/LAP score in CML

Low

Eosinophilia definition

Absolute eosinophil count >0.4 × 10⁹/L

Most common causes of eosinophilia

Allergic disorders and parasitic infections

Hypereosinophilic syndrome

Persistent eosinophilia >1.5 × 10⁹/L for >6 months causing tissue damage

Basophilia definition

Absolute basophil count >0.1 × 10⁹/L

Most important cause of basophilia

Chronic myeloid leukemia (CML)

Monocytosis definition

Absolute monocyte count >0.8 × 10⁹/L

Common causes of monocytosis

TB, endocarditis, brucellosis, RA, SLE

Lymphocytosis

Increased absolute lymphocyte count

Most common cause of lymphocytosis

Viral infections

Classic features of infectious mononucleosis

Fever, sore throat, lymphadenopathy, atypical lymphocytes

Most common cause of infectious mononucleosis

Epstein-Barr virus (EBV)

Neutropenia

Reduced absolute neutrophil count below normal

Kostmann syndrome

Autosomal recessive congenital neutropenia causing severe infant infections

Drug-induced neutropenia mechanism

Direct toxicity or immune-mediated destruction

Lymphopenia causes

HIV, corticosteroids, immunosuppressive therapy, bone marrow failure

Best investigation for qualitative leukocyte abnormalities

Peripheral blood smear

Most important peripheral blood findings to recognize

Hypersegmentation, toxic granulation, Dohle bodies, Pelger cells, giant granules

High-yield association: Hypersegmented neutrophils

Megaloblastic anemia

High-yield association: Toxic granulation + Dohle bodies

Reactive bacterial infection

High-yield association: High LAP score

Leukemoid reaction; Low LAP score

High-yield association: Giant granules in neutrophils

Chediak-Higashi syndrome

High-yield association: Bilobed neutrophils

Pelger-Huët anomaly

High-yield association: Atypical lymphocytes

Infectious mononucleosis

High-yield association: Eosinophilia + parasites

Helminthic infection