The reference range for adults (males and females) is as follows:
Total leukocytes: 4.00-11.0 x 10 9/L
Neutrophils: 2.5–7.5 x 10 9/L
Lymphocytes: 1.5–3.5 x 10 9/L
Monocytes: 0.2–0.8 x 10 9/L
Eosinophils: 0.04-0.4 x 10 9/L
Basophils: 0.01-0.1 x 10 9/L
A white blood cell (WBC) count of less than 4 x 109/L indicates leukopenia.
A WBC count of more than 11 x 109/L indicates leukocytosis.
Decreased WBC count, leukopenia, is seen when supply is depleted by infection or treatment such as chemotherapy or radiation therapy, or when a hematopoietic stem cell abnormality does not allow normal growth/maturation within the bone marrow, such as myelodysplastic syndrome or leukemia. Leukopenia (decrease in WBC) is most often due to a lower number of neutrophils, referred to as neutropenia. Characteristically, the neutrophil count is less than 1.5 x 109/L. [1, 2]
Elevated WBC, leukocytosis, is seen in response to infection, stress, inflammatory disorders (referred to as reactive leukocytosis), or abnormal production as in leukemia. An increased WBC count can be due to an individual cell component or a combination, depending on the cause. Malaise, chills, and fever, related to infection, are clinically seen in both leukopenia and neutrophilic leukocytosis.
Reactive leukocytosis can be classified on the basis of the white blood cell type affected. Criteria as well as common causes are below.
Neutrophilic leukocytosis occurs when neutrophils are greater than 7.5 x 109/L. Common causes are as follows:
Acute bacterial infections 
Sterile inflammation/tissue necroses seen in myocardial infarction, burns, crush injuries.
Eosinophilic leukocytosis occurs when eosinophils are greater than 0.4 x 109/L. Common causes are as follows:
Basophilic leukocytosis occurs when basophils are greater than 0.1 x 109/L. Causes include rare allergic reactions (IgE mediated).
Monocytosis occurs when monocytes are greater than 0.8 x 109/L. Common causes include the following:
Chronic infections such as tuberculosis
Collagen vascular disease
Inflammatory bowel disease
Lymphocytosis occurs when lymphocytes are greater than 3.5 x 109/L. Common causes are as follows:
Viral infections such as hepatitis A, cytomegalovirus (CMV), Epstein-Barr virus (EBV)
Neoplastic proliferations of white blood cells also cause leukocytosis. These are the malignant proliferations of abnormal clones of white blood cells within the bone marrow that are broadly categorized into lymphoid and myeloid neoplasms depending on the type of white cell proliferation. These malignancies are further characterized by the maturity and differentiation of the individual cell types and are divided into acute leukemias such as acute myeloid leukemia and acute lymphoblastic leukemia and chronic leukemias such as chronic myeloid leukemia and chronic lymphocytic leukemia.
Collection and Panels
Collection details are as follows:
Specimen: Whole blood
Collection: The blood sample is drawn into a vacuumized purple top tube containing an anticoagulant, ethylenediaminetetraacetic acid (EDTA). This chemical agent prevents the blood sample from clotting.
Panel: Complete blood count
The white blood cell count (WBC) is a component of a complete blood cell count (CBC) and is the enumeration of white blood cells in a small volume of whole blood. The testing is performed on an automated hematology analyzer. The white blood cells (leukocytes) are further divided into phagocytes or myeloid (neutrophils, eosinophils, basophils, monocytes) and immunocytes or lymphoid (lymphocytes). 
The total white blood cell count is expressed as an absolute number and is further divided into subtypes of white blood cells by a differential WBC count, which is expressed as a percentage and absolute number. Different characteristics of the nuclei and cytoplasm of the cell allow differentiation by instrumentation and microscopy. For microscopy, a blood smear is prepared and stained with a dye preparation called Giemsa stain. These white blood cell types, staining characteristics, and associations are outlined in Table 1.
Table 1. White Blood Cell Types, Characteristics, and Associations (Open Table in a new window)
|Neutrophil||Multilobulated nucleus with small pale pink cytoplasmic granules||Acute infection, bacterial and fungal|
|Lymphocyte||Mononuclear, scant to moderate blue cytoplasm, occasional cytoplasmic granules||Chronic infection and viral infection|
|Monocyte||Single folded nucleus, blue-gray cytoplasm, occasional cytoplasmic granules and vacuoles||Chronic infection|
|Eosinophil||Bilobed nucleus, large pink cytoplasmic granules||Allergic reaction, parasitic infection|
|Basophil||Bi-lobed nucleus, large brown-black cytoplasmic granules||Allergic reactions, blast crisis in chronic myeloid leukemia|
|Immature granulocytes||Include metamyelocytes, myelocytes, promyelocytes, and/or blasts||Infections, growth factor therapy, chronic leukemia, and acute leukemia. Commonly referred to as "left shift."|
Formed in the bone marrow by multipotential progenitor cells/hematopoietic stem cells (hematopoiesis), white blood cells are a part of our immune system and play an essential role in protecting the body against infection. The peripheral blood white blood cell count (WBC) and differential count is used to assess the body’s response to certain benign conditions such as acute and chronic infections, inflammatory conditions, allergic reactions, and immunodeficiency states and various hematologic malignancies such as leukemias and lymphomas. It is also used to monitor the response to chemotherapy, growth factors, and immunosuppressive therapies. [7, 8, 9, 10]
Normal black and Middle Eastern subjects may have lower normal white cell counts. In normal pregnancy, the upper limits are slightly high for total leukocytes (14.5 x 109/L) and neutrophils (11 x 109/L).