For accurate clinical interpretation, it is essential to report the absolute count of leukocytes. This value is calculated as follows:
Absolute Leukocyte Count = Leukocyte% × Total Leukocyte Count/ml
Neutrophilia
Neutrophilia, or neutrophilic leukocytosis, is characterized by an absolute neutrophil count exceeding 7,500/μl.
Causes of Neutrophilia
- Acute Bacterial Infections: Such as abscesses, pneumonia, meningitis, septicemia, acute rheumatic fever, and urinary tract infections.
- Tissue Necrosis: Resulting from burns, injuries, and myocardial infarction.
- Acute Blood Loss and Hemorrhage
- Myeloproliferative Disorders
- Metabolic Disorders: Including uremia, acidosis, and gout.
- Poisoning
- Malignant Tumors
- Physiological Factors: Including exercise, labor, pregnancy, and emotional stress.
In cases where the total leukocyte count exceeds 50,000/cmm and immature cells resembling leukemia are present in peripheral blood, a Leukemoid Reaction may be observed. This condition, although mimicking leukemia, occurs in non-leukemic disorders and can be caused by:
- Severe bacterial infections like septicemia and pneumonia
- Severe hemorrhage or acute hemolysis
- Poisoning or burns
- Carcinomas metastatic to the bone marrow
Differentiating a leukemoid reaction from chronic myeloid leukemia is crucial. The table below outlines key distinctions between the two:
| Parameter | Leukemoid Reaction | Leukemia |
|---|---|---|
| Clinical Presentation | Features of underlying disease; fever common | Splenomegaly |
| Examination of Blood | ||
| Total leukocyte count | <50000/μl | Variable; usually > 100,000/μl |
| Course of netrophilia | Disappears with resolution of underlying disease | Progressive increase |
| Evidence of infection | Toxic granules; Döhle inclusion bodies | Absent |
| Basophilia | Absent | Present |
| Immature cells | Few; cells up to myelocyte stage | Many; cells up to blasts |
| Examination of Marrow | Myeloid hyperplasia | Increased blasts and immature cells of neutrophil series; suppression of other cell lines |
| Clonality | Polyclonal | Monoclonal |
| Karyotype | Normal | Abnormal |
Neutropenia
Neutropenia is defined as an absolute neutrophil count below 2,000/μl and is categorized as mild (2,000-1,000/μl), moderate (1,000-500/μl), and severe (< 500/μl).
Causes of Neutropenia
- Decreased or Ineffective Production in Bone Marrow:
- Infections
- Bacterial: Typhoid, paratyphoid, miliary tuberculosis, septicemia
- Viral: Influenza, measles, rubella, infectious mononucleosis, infective hepatitis
- Protozoal: Malaria, kala azar
- Overwhelming Infection by Any Organism
- Hematologic Disorders: Megaloblastic anemia, aplastic anemia, aleukemic leukemia, myelophthisis
- Drugs:
- Idiosyncratic Action: Analgesics, antibiotics, sulfonamides, phenothiazines, antithyroid drugs, anticonvulsants
- Dose-Related: Anticancer drugs
- Ionizing Radiation
- Congenital Disorders: Kostman syndrome, cyclic neutropenia, reticular dysgenesis
- Infections
- Increased Destruction in Peripheral Blood:
- Neonatal isoimmune neutropenia
- Systemic lupus erythematosus
- Felty's syndrome
- Increased Sequestration in the Spleen:
- Hypersplenism
Eosinophilia
Eosinophilia refers to an absolute eosinophil count greater than 600/μl.
Causes of Eosinophilia
- Allergic Diseases: Including bronchial asthma, rhinitis, urticaria, and reactions to drugs.
- Skin Disorders: Such as eczema, pemphigus, and dermatitis herpetiformis.
- Parasitic Infections with Tissue Invasion: Examples include filariasis, trichinosis, and echinococcosis.
- Hematologic Disorders: Chronic myeloproliferative disorders, Hodgkin’s disease, peripheral T-cell lymphoma.
- Carcinoma with Necrosis
- Radiation Therapy
- Lung Diseases: Such as Loeffler’s syndrome and tropical eosinophilia.
- Hypereosinophilic Syndrome
Basophilia
Basophilia is characterized by an increase in basophils in the blood exceeding 100/μl. This condition is often observed in chronic myeloid leukemia, polycythemia vera, idiopathic myelofibrosis, basophilic leukemia, myxedema, and hypersensitivity reactions to food or drugs.
Monocytosis
Monocytosis is defined as an absolute monocyte count above 1,000/μl.
Causes of Monocytosis
- Infections: Such as tuberculosis, subacute bacterial endocarditis, malaria, and kala azar.
- Recovery from Neutropenia
- Autoimmune Disorders
- Hematologic Diseases: Including myeloproliferative disorders, monocytic leukemia, and Hodgkin’s disease.
- Other Conditions: Chronic ulcerative colitis, Crohn’s disease, sarcoidosis.
Lymphocytosis
Box 1: Differential diagnosis of Lymphocytosis
- Mature lymphocytosis: Viral infections, whooping cough, tuberculosis, infectious lymphocytosis, chronic lymphocytic leukemia
- Atypical lymphocytosis: Infectious mononucleosis, cytomegalovirus, toxoplasmosis, infectious hepatitis
- Lymphoblasts: Acute lymphoblastic leukemia
Lymphocytosis is defined as an increase in the absolute lymphocyte count above the normal upper limit for age—4,000/μl in adults, >7,200/μl in adolescents, and >9,000/μl in children and infants.
Causes of Lymphocytosis
- Infections:
- Viral: Including acute infectious lymphocytosis, infective hepatitis, cytomegalovirus, mumps, rubella, varicella
- Bacterial: Pertussis, tuberculosis
- Protozoal: Toxoplasmosis
- Hematological Disorders: Such as acute lymphoblastic leukemia, chronic lymphocytic leukemia, multiple myeloma, and lymphoma.
- Other Causes: Serum sickness, post-vaccination, and drug reactions.