White Blood Cell Count, Blood Smear and Differential Core Lab Study
Synonym/Acronym
WBC with diff, leukocyte count, white cell count.
Rationale
To evaluate bacterial, parasitic, and viral infections; to assist in diagnosing conditions related to immune response such as asthma, dermatitis, and hay fever; and to assist in diagnosing and monitoring leukemic disorders.
A small group of studies in this manual have been identified as Core Lab Studies. The designation is meant to assist the reader in sorting the basic always need to know laboratory studies from the hundreds of other valuable studies found in the manuala way to begin putting it all together.
Normal, abnormal, or various combinations of core lab study results can indicate that all is well, reveal a problem that requires further investigation with additional testing, signal a positive response to treatment, or suggest that the health status is as expected for the associated situation and time frame.
White blood cell (WBC) count is part of a complete blood count (CBC), one of the most requested laboratory studies, and is included in the Anemia profile, General Health panel, and Obstetric panel.
Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.
Normal Findings
Method: Automated, computerized, multichannel analyzers, flow cytometry. Many analyzers can determine a five- or six-part WBC differential. The six-part automated WBC differential identifies and enumerates neutrophils, lymphocytes, monocytes, eosinophils, basophils, and immature granulocytes (IG), where IG represents the combined enumeration of promyelocytes, metamyelocytes, and myelocytes as both an absolute number and a percentage. The five-part WBC differential includes all but the immature granulocyte parameters.
WBC Count and Differential
*SI Units (conventional units × 1 or WBC count × 109/L). |
WBC Count and Differential
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Reference values for the WBC count vary across the age continuum and with physical condition. For example, counts are affected by high levels of physical activity or stress (e.g., labor and delivery). Thus, the time of collection and the activity status of the patient should be taken into consideration when reviewing or comparing WBC counts.
Timely notification to the requesting health-care provider (HCP) of any critical findings and related symptoms is a role expectation of the professional nurse. A listing of these findings varies among facilities.
Consideration may be given to verifying the critical findings before action is taken. Policies vary among facilities and may include requesting immediate recollection and retesting by the laboratory.
The presence of abnormal cells, other morphological characteristics, or cellular inclusions may signify a potentially life-threatening or serious health condition and should be investigated. Examples are hypersegmented neutrophils, agranular neutrophils, blasts or other immature cells, Auer rods, Döhle bodies, marked toxic granulation, and plasma cells.
Study type: Blood from a lavender-top [EDTA] tube; related body system: . The specimen should be mixed gently by inverting the tube 10 times. The specimen should be analyzed within 24 hr when stored at room temperature or within 48 hr if stored at refrigerated temperature. If it is anticipated the specimen will not be analyzed within 24 hr, two blood smears should be made immediately after the venipuncture and submitted with the blood sample. Smears made from specimens older than 24 hr may contain an unacceptable number of misleading artifactual abnormalities of the WBCs, such as necrobiotic WBCs.
WBCs constitute the bodys primary defense system against foreign organisms, tissues, and other substances. The life span of a normal WBC is 13 to 20 days. Old WBCs are destroyed by the lymphatic system and excreted in the feces. Reference values for WBC counts vary significantly with age. WBC counts vary diurnally, with counts being lowest in the morning and highest in the late afternoon. Other variables such as stress and high levels of activity or physical exercise can trigger transient increases of 2 × 103/microL to 5 × 103/microL. The main WBC types are neutrophils (band and segmented neutrophils), eosinophils, basophils, monocytes, and lymphocytes. WBCs are produced in the bone marrow. B-cell lymphocytes remain in the bone marrow to mature. T-cell lymphocytes migrate to and mature in the thymus. An increased WBC count is termed leukocytosis, and a decreased WBC count is termed leukopenia.
A total WBC count indicates the degree of response to a pathological process, but a more complete evaluation for specific diagnoses for any one disorder is provided by the differential count. The WBCs in the count and differential are reported as an absolute value and as a percentage. The relative percentages of cell types are arrived at by basing the enumeration of each cell type on a 100-cell count. The absolute value is obtained by multiplying the relative percentage value of each cell type by the total WBC count. For example, on a CBC report, with a total WBC of 9 × 103/microL and WBC differential with 92% segmented neutrophils, 1% band neutrophils, 5% lymphocytes, and 1% monocytes the absolute values are calculated as follows: 92/100 × 9 = 8.3 segs, 1/100 × 9 = 0.09 bands, 5/100 × 9 = 0.45 lymphs, 1/100 × 9 = 0.1 monos for a total of 9 WBC count. The absolute neutrophil count (ANC) for this patient would be 9 × (0.92 + 0.01) = 8.4.
The WBC count can be performed alone with the differential cell count or as part of the complete blood count (CBC). The WBC differential can be performed by an automated instrument or manually on a slide prepared from a stained peripheral blood sample. Automated instruments provide excellent, reliable information, but the accuracy of the WBC count can be affected by the presence of circulating nucleated red blood cells (RBCs), clumped platelets, fibrin strands, cold agglutinins, cryoglobulins, intracellular parasitic organisms, or other significant blood cell inclusions and may not be identified in the interpretation of an automated blood count. The decision to report a manual or automated differential is based on specific criteria established by the laboratory. The criteria are designed to identify findings that warrant further investigation or confirmation by manual review.
The ANC reflects the number of segmented and band type neutrophils in the total WBC count. It is used as an indicator of immune status because it reflects the type and number of WBC available to rapidly respond to an infection. Neutropenia is a decrease below normal in the number of neutrophils. ANC = Total WBC × [(Segs/100) + (Bands/100)] or total WBC × (% Segs + % Bands). The normal value varies with age but in general mild neutropenia is less than 1.5, moderate neutropenia is between 0.5 and 1, and severe neutropenia is less than 0.5. The ANC is helpful when managing patients receiving chemotherapy. It can drive decisions to place a hospitalized patient in isolation in order to protect the patient from exposure to infectious agents. Patients who are aware of their ANC can also make informed decisions in taking actions to avoid exposure to crowds, avoid touching things in public places that may carry germs, or avoid friends and family who may be sick.
Acute leukocytosis is initially accompanied by changes in the WBC count population, followed by changes within the individual WBCs. Leukocytosis usually occurs by way of increase in a single WBC family rather than a proportional increase in all cell types. Toxic granulation and vacuolation are commonly seen in leukocytosis accompanied by a shift to the left, or increase in the percentage of immature neutrophils to mature segmented neutrophils. An increased number or percentage of immature granulocytes, reflected by a shift to the left, represents production of WBCs and is useful as an indicator of infection. Immature neutrophils are called bands and can represent 3% to 5% of total circulating neutrophils in healthy individuals. Bandemia is defined by the presence of greater than 6% to 10% band neutrophils in the total neutrophil cell population. These changes in the white cell population are most commonly associated with an infectious process, usually bacterial, but they can occur in healthy individuals who are under stress (in response to epinephrine production), such as women in childbirth and very young infants. The WBC count and differential of a woman in labor or of an actively crying infant may show an overall increase in WBCs with a shift to the left. Before initiating any kind of intervention, it is important to determine whether an increased WBC count is the result of a normal condition involving physiological stress or a pathological process. The use of multiple specimen types may confuse the interpretation of results in infants. Multiple samples from the same collection site (i.e., capillary versus venous) may be necessary to obtain an accurate assessment of the WBC picture in these young patients.
Neutrophils
Neutrophils are normally found as the predominant WBC type in the circulating blood. Also called polymorphonuclear cells, they are the bodys first line of defense through the process of phagocytosis. They also contain enzymes and pyogenes, which combat foreign invaders.
Lymphocytes
Lymphocytes are agranular, mononuclear blood cells that are smaller than granulocytes. They are found in the next highest percentage in normal circulation. Lymphocytes are classified as B cells and T cells. Both types are formed in the bone marrow, but B cells mature in the bone marrow and T cells mature in the thymus. Lymphocytes play a major role in the bodys natural immune defense system. B cells differentiate into immunoglobulin-synthesizing plasma cells. T cells function as cellular mediators of immunity and comprise helper/inducer (CD4) lymphocytes, delayed hypersensitivity lymphocytes, cytotoxic (CD8 or CD4) lymphocytes, and suppressor (CD8) lymphocytes.
Monocytes
Monocytes are mononuclear cells similar to lymphocytes, but they are related more closely to granulocytes in terms of their function. They are formed in the bone marrow from the same cells as those that produce neutrophils. The major function of monocytes is phagocytosis. Monocytes stay in the peripheral blood for about 70 hr, after which they migrate into the tissues and become macrophages.
Eosinophils
The main function of eosinophils is response to allergy-inducing substances and parasites and phagocytosis of antigen-antibody complexes. Eosinophils have granules that contain histamine used to kill foreign cells in the body. Eosinophils also contain proteolytic substances that damage parasitic worms. The binding of histamine to receptor sites on cells results in smooth muscle contraction in the bronchioles and upper respiratory tract, constriction of pulmonary vessels, increased mucus production, and secretion of acid by the cells that line the stomach. The contents of eosinophilic granules are very effective in neutralizing allergens. However, the substances released by the eosinophils can also damage normal cells in the area where the histamine and other enzymes are released. Eosinophil counts can increase to greater than 30% of normal in parasitic infections; however, a significant percentage of children with visceral larva migrans infestations have normal eosinophil counts.
A nasal smear can be examined for the presence of eosinophils to screen for allergic conditions. Either a single smear or smears of nasal secretions from each side of the nose should be submitted, at room temperature, for Hansel staining and evaluation. Normal findings vary by laboratory, but generally, greater than 10% to 15% is considered eosinophilia, or increased presence of eosinophils.
Basophils
Basophils are found in small numbers in the circulating blood. They have a phagocytic function and, similar to eosinophils, contain numerous specific granules. Basophilic granules contain heparin, histamines, and serotonin. Basophils may also be found in tissue and as such are classified as mast cells. Basophilia is noted in conditions such as leukemia, Hodgkin disease, polycythemia vera, ulcerative colitis, nephrosis, and chronic hypersensitivity states.
Factors That May Alter the Results of the Study
Other Considerations
Increased In
Leukocytosis
Decreased In
Leukopenia
Neutrophils Increased (Neutrophilia)
Neutrophils Decreased (Neutropenia)
Lymphocytes Increased (Lymphocytosis)
Lymphocytes Decreased (Lymphopenia)
Monocytes Increased (Monocytosis)
Eosinophils Increased (Eosinophilia)
Eosinophils are released and migrate to inflammatory sites in response to numerous environmental, chemical/drug, or immune-mediated triggers. T cells, mast cells, and macrophages release cytokines, such as interlukin-3 (IL3), interlukin-5 (IL5), granulocyte/macrophage colony-stimulating factor, and chemokines such as the eotaxins, which can result in the activation of eosinophils.
Eosinophils Decreased (Eosinophilia)
Potential Nursing Problems: Assessment & Nursing Diagnosis
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Before the Study: Planning and Implementation
Teaching the Patient What to Expect
After the Study: Implementation & Evaluation Potential Nursing Actions
Treatment Considerations
Fever
Fluid Volume
Infection
Nutritional Considerations
Clinical Judgement
Follow-Up and Desired Outcomes