A Closer Look at Common White Blood Cell Disorders

Learn about the types, testing methods and what the future holds.

By Karen Appold

In some instances, change is not good. For example, when white blood cells (WBCs) change from normal to abnormal, it is most likely an indicator that something is wrong.

Common WBC disorders include both quantitative and qualitative conditions, says Karen A. Brown, MS, MT(ASCP), CLS(NCA), associate professor and MLT program director, University of Utah , Salt Lake City . Neutrophils are the most numerous leukocytes in the peripheral blood of an adult, so quantitative changes in these cells are a significant finding in any patient.

Normal neutrophil counts vary with age and race, Brown says, as neutrophils in adults are defined as greater than 7.0 x 10 9/L. Because neutrophils function primarily in fighting bacterial infections, neutrophilia is most associated with these types of infections. However, other organisms may cause a neutrophilia. Likewise, other conditions may induce an increase in neutrophils as a reactive response and include inflammatory processes, metabolic abnormalities such as uremia or gout, neoplasms, some chemicals and drugs, and physiological factors such as exercise, pain and stress. A neutrophilia may also result after treatment with colony-stimulating growth factors.

Neutropenia is defined as a neutrophil count less than 2.0 x 10 9/L in whites and less than 1.5 x 10 9/L in blacks, Brown says. Some causes of neutropenia include viral infections, overwhelming bacterial infections that might be associated with sepsis, physical agents and chemicals (e.g., radiation and benzene), drugs (e.g., chemotherapeutic agents, anti-inflammatories, antihistamines) and alloantibodies or autoantibodies.

The second most numerous leukocytes in the peripheral blood are lymphocytes, Brown says. Lymphocytes function primarily in the body’s immunologic defense processes. Three broad groups of lymphocytic disorders are defined as:

1. Nonmalignant conditions involving quantitative changes in lymphocytes resulting from viral infections, inflammatory processes or numerous other causes. A common viral disorder in this group is infectious mononucleosis.

2. Disorders that represent functional abnormalities expressed as impaired cellular or humoral immunity. A common disease in this category is multiple myeloma.

3. Malignant lymphoproliferative disorders such as acute lymphoblastic leukemia, chronic lymphocytic leukemia, Hodgkin’s lymphoma and non-Hodgkin’s lymphoma.

Other types of leukemia, i.e., acute myeloblastic (AML) and chronic myelogenous (CML), should be considered WBC disorders, Brown says. The incidences of the many subgroups of AML as well as CML are variable.

Further Examination
Increases in the number of white blood cells are usually reactive, but must be distinguished from the increased cell counts seen in the myeloproliferative disorders and acute leukemias, says Sandra C. Hollensead, MD, MT(ASCP), associate professor of Pathology, University of Louisville School of Medicine, Department of Pathology, and medical director, Hematology and Coagulation laboratories, University of Louisville (KY) Hospital.

Chronic myelogenous leukemia, polycythemia rubra vera, essential thrombocythemia and myelofibrosis comprise the myeloproliferative disorders. Two rare disorders, chronic neutrophilic leukemia and chronic eosinophilic leukemia, are also classified as myeloproliferative diseases. Patients with a myeloproliferative disorder will commonly have an enlarged spleen, because these are forms of chronic leukemia. The myeloproliferative disorders show similar findings on a bone marrow exam, including hypercellularity, clustering of dysplastic megakaryocytes, absence of bone marrow iron stores and fibrosis. The classification of the myeloproliferative disorders comes in large part from review of a CBC and peripheral smear.

Neutrophilia: Reactive versus Neoplastic
When evaluating a peripheral blood film for neutrophilia, Dr. Hollensead says morphologic clues can be used to determine if the elevated count is reactive (leukemoid reaction) or neoplastic (chronic myelogenous leukemia).

Leukemoid reactions are characterized by a shift to the left in granulocyte maturation; however, the cells retain a normal “inverse pyramid” of maturation. Segmented neutrophils will predominate; bands will be next in frequency, followed by metamyelocytes and myelocytes, Dr. Hollensead says. Circulating blasts and nucleated red blood cells are not usually seen in a leukemoid reaction and, when present, suggest leukemia. The granulocytes in infection will show toxic granulation, cytoplasmic vacuoles and Döhle bodies.

In CML, immature granulocytes predominate and circulating myeloblasts with nucleated red blood cells will be present. In fact, Dr. Hollensead says chronic myelogenous leukemia has been called “bone marrow in the blood,” as all stages of cell maturation can be seen, similar to a bone marrow aspirate. In addition, the number of basophils and eosinophils will often be increased. The basophils will typically be small and dysplastic and perhaps difficult to recognize as basophils. Other cytophilias may accompany CML, such as increased platelet counts (i.e., thrombophilia) or increased red cell counts (i.e., polycythemia).

Morphologic clues can be enhanced in difficult cases with a leukocyte alkaline phosphatase (LAP) score, which will be elevated in leukemoid reaction but normal or low in CML.

Acute myeloid leukemias are characterized by circulating myeloblasts and greater than 20 percent myeloblasts in the bone marrow, Dr. Hollensead says. The presenting white blood cell count may be elevated, decreased or normal, so recognition of circulating myeloblasts is critical. Accompanying the circulating blasts are circulating nucleated red blood cells and decreased hemoglobin and hematocrit. Platelet count may also be decreased and patients often first present symptoms of thrombocytopenia with petechiae and bleeding. The classification of acute myeloid leukemias is done through bone marrow differential counts, rather than peripheral blood counts, as with the myeloproliferative disorders. However, the appearance of the blasts and the degree of differentiation of the white cells in the peripheral blood are used to aid in the correct classification of the leukemia.

According to Dr. Hollensead, an abbreviated explanation of the French American British (FAB) classification of acute myeloid leukemia is as follows:

M0: Myeloblastic leukemia minimally differentiated

M1: Myeloblastic leukemia without maturation

M2: Myeloblastic leukemia with maturation

M3: Hypergranular promyelocytic leukemia (also has a microgranular variant)

M4: Myelomonocytic leukemia (also has a marrow eosinophilia variant M4e)

M5: Monocytic leukemia (may be poorly differentiated M5a or differentiated

M5b)

M6: Erythroleukemia

M7: Megakaryoblastic leukemia

The World Health Organization (WHO) has further modified this basic morphologic classification to group white blood cells disorders by incorporating cytogenetic and clinical information, Dr. Hollensead says.

Lymphocytosis: Reactive Versus Neoplastic
An increase in the absolute number of lymphocytes is usually reactive and most often due to a viral illness, Dr. Hollensead says. The Downey type I lymphocyte is rare in infectious mononucleosis but may be prominent in the infection of young children. The cells are small with indented nuclei, condensed “clumped” chromatin and scant cytoplasm. Downey type II lymphocytes exhibit abundant cytoplasm with radiating basophilia (light staining areas separated by line-like darker staining areas) and cytoplasm indented by red blood cells.

Symptoms include fever, malaise, loss of appetite, sore throat and swollen glands, says Bernadette Rodak, MS, CLSpH(NCA), associate professor, Indiana University , Indianapolis , IN. It is more common among teenagers, although any age group can be affected. Some patients may exhibit splenomegaly. The reactive lymphocytes have been shown to be differentiated T cells.

Downey type III lymphocytes are large with moderate basophilic cytoplasm, coarse nuclear chromatin and a prominent nucleolus, Dr. Hollensead says. These are also known as immunoblasts. In reactive lymphocytosis, the lymphocytes are a polymorphous population. Small unremarkable lymphs will be seen, but also enlarged lymphocytes with abundant blue cytoplasm will be noted. Often, the cells will show scalloping of the cytoplasm, being indented by surrounding red blood cells. Some of the lymphocytes will be plasmacytoid and some will show deep basophilic cytoplasm similar to lymphoblasts. However, true lymphoblasts with nucleoli are not seen. In reactive lymphocytosis, hemoglobin is normal, no circulating nucleated red blood cells are seen and platelet counts are normal. WBC count may be overall decreased, elevated or within normal limits.

Neoplastic proliferation of lymphocytes is seen in acute and chronic lymphoid leukemia, Dr. Hollensead says. Also, non-Hodgkin’s lymphoma cells can enter the blood as a leukemic phase of the lymphoma. An increased nuclear:cytoplasmic ratio and basophilic cytoplasm characterize these lymphocytes. Nucleoli may be seen and the nuclear outlines may be irregular. The lymphocytes may be small (similar to the size of a normal lymphocyte), large (similar to or larger than a monocyte) or a mixture of large and small lymphocytes. Flow cytometry performed on the peripheral blood is helpful in characterizing these lymphocytes as circulating lymphoma cells.

Chronic lymphocytic leukemia is characterized by an elevated WBC count, Dr. Hollensead says, composed predominately of mature appearing lymphocytes with scant cytoplasm. The nucleus of these cells shows a dense and compacted chromatin with pale staining lines, known as “cracked earth” nuclear chromatin. Many smudged cells or “basket” cells are also seen. A morphologic clue to the disorder is the monotonous appearance of the lymphocytes, as opposed to the varied appearance of reactive lymphocytes. One of the consequences of chronic lymphocytic leukemia is prolymphocytic transformation. Prolymphocytes are large lymphocytes seen in the peripheral blood and bone marrow with a prominent single nucleolus and abundant pale blue cytoplasm. Recognition of these lymphocytes is an important clue in recognizing the transformation.

Hairy cell leukemia is a type of lymphocytic leukemia characterized by circulating lymphocytes with abundant cytoplasm having an irregular outline of the cytoplasmic membrane. The nucleus has a smudged quality. Circulating nucleated red blood cells are seen. Pancytopenia is usually present and the patient will have a markedly enlarged spleen, Dr. Hollensead says. The cells may be infrequent, so recognizing them can be most helpful in determining the cause of pancytopenia.

Mycosis fungoides is caused by a primary T cell lymphoma of the skin, Dr. Hollensead says. When peripheral lymphocytosis develops with circulating abnormal T lymphocytes and exfoliative erythroderma, it is called Sezary syndrome; and the abnormal lymphocytes are called Sezary cells. The cells are recognizable by marked convolutions of the nuclei giving them a cerebriform or “brain-like” appearance. Cytoplasm may be abundant or scant. Nucleoli are absent or inconspicuous, as the cells have a more mature appearance. Detection of Sezary cells is important; patients with Sezary syndrome have a poorer prognosis than those with classic Mycosis fungoides. Cells similar in appearance can also circulate in the peripheral blood of patients with the diagnosis of peripheral T-cell lymphoma.

A subset of the mature T cell neoplasms is T cell large granular lymphocyte leukemia, Dr. Hollensead says. In this disorder, large lymphocytes with abundant cytoplasm and coarse azurophilic granules predominate in the blood and bone marrow. Recognition of the cells on peripheral blood film may be helpful in making a diagnosis because the disorder often has an indolent clinical course, frequently accompanied by neutropenia with or without anemia.

Acute lymphocytic leukemia (ALL) is characterized by circulating lymphoblasts, which may have subtle morphologic findings. Acute lymphocytic leukemia is classified as L1-L3. A monotonous population of lymphoblasts, which are small lymphocytes with scant cytoplasm, characterizes the L1 variant of ALL as well as open, fine evenly dispersed nuclear chromatin. Nucleoli are absent or small and inconspicuous, Dr. Hollensead says. Nuclei may be indented or irregular in outline of the nuclear membrane. These lymphocytes may be considered normal by the inexperienced morphologist and, because L1 occurs predominately in children, the lymphocytosis may not cause concern.

The L2 variant shows maturation of the lymphocytes and is the most common variant of ALL in adults. Because the population is polymorphous, Dr. Hollensead says the morphologist may consider the cells to be reactive rather than leukemic. The lymphoblasts are larger than in L1 and the nuclei are more irregular with prominent nucleoli. Finding circulating nucleated red blood cells and accompanying anemia and thrombocytopenia helps to recognize ALL as a neoplastic process rather than a reactive condition. The L3 (i.e., Burkitt type) subtype is the most uncommon, but perhaps the most striking morphologically, according to Dr. Hollensead.The lymphoblasts are large, with abundant vacuolated cytoplasm, eccentric nuclei and finely divided chromatin often containing multiple basophilic medium-sized nucleoli. The cytoplasm is distinctly basophilic and the cytoplasmic lipid vacuolization prominent. Flow cytometry is again useful in analyzing these peripheral blood lymphocytes.

In the WHO classification the FAB L1 and L2 variants are classified together as precursor B-lymphoblastic leukemia/lymphoma, and the L3 variant is included as part of the mature B-cell neoplasms as Burkitt lymphoma/leukemia, Dr. Hollensead says. The WHO classification includes a category of precursor T lymphoblastic leukemia/lymphoma, making classification of the lymphocytes by flow cytometry as of B or T cell lineage required for proper classification.

Neutropenia: Acquired Versus Constitutional
Isolated neutropenia, i.e., decreased neutrophil count, has many causes, Dr. Hollensead says. Infection, with depletion of neutrophils caused by destruction in fighting the infectious agent, is the most common cause. In these cases, the peripheral smear may show general changes of infection, including toxic granulation and left shift in the granulocytes.

Neutropenia also may be caused by destruction of neutrophils by antibodies associated with immune diseases, by drug reactions, as part of megaloblastic anemia or because of pooling in the spleen, Dr. Hollensead says. In these cases of peripheral destruction, white cell morphology on peripheral smear exam will show no changes. However, peripheral destruction of neutrophils can be suggested as the cause of neutropenia if other parameters of the CBC are within normal limits and no abnormal morphology of any cell line is seen on peripheral smear. New onset neutropenia often necessitates a bone marrow exam to rule out a bone marrow disorder.

Neutropenia is also associated with constitutional disorders in infancy and childhood, Dr. Hollensead says. The most common of these rare hereditary disorders are cyclic neutropenia, Kostmann’s syndrome and Chediak-Higashi syndrome. Cyclic neutropenia is characterized by episodes of neutropenia followed by rebound recovery without WBC abnormalities. In Kostmann’s syndrome and Chediak-Higashi syndrome, neutropenia is sustained and severe. Kostmann’s syndrome shows abnormalities of the granulocyte precursors in the bone marrow, while Chediak-Higashi syndrome shows white blood cells with massively enlarged granules. In this autosomal recessive disease, granule structure and function is defective in all granulated hematopoietic cells of the body. The abnormality affects granulocytes, lymphocytes, eosinophils, basophils, monocytes and platelets. Infections are caused by both impaired motility of granulocytes and defective degranulation.

Tried and True Tests
In addition to already mentioned tests, Dr. Hollensead says cytogenetic analysis of the white blood cells is important in diagnosing myeloproliferative diseases, myelodysplastic syndromes and in classification of leukemias. For example, the Philadelphia chromosome and/or the BCR/ABL fusion gene must be present to diagnose chronic myelogenous leukemia.

Brown provides this list of disorders and related tests:

• Quantitative neutrophilic and lymphocytic disorders: Total WBC count and examination of peripheral blood smear.
• Infectious Mononucleosis: As above plus rapid test (latex agglutination).
• Multiple myeloma: As above for quantitative disorders, ESR, serum protein electrophoresis and immunoelectrophoresis.
• Leukemia: As above for quantitative disorders plus immunophenotyping, cytogenetics, molecular studies and cytochemistry.
• Lymphomas: Not usually diagnosed by peripheral blood studies but through cytogenetics, molecular studies and immunophenotyping.

Testing Methods on the Horizon
Examination of the peripheral blood smear and correlation with CBC parameters offers a wealth of clinically pertinent information through morphologic clues, Dr. Hollensead says, when performed by an astute hematologic morphologist. Noting these findings in the CBC report or in a clinical pathology consult report can be beneficial to the clinician and helps provide a cost-effective means to diagnose patients.

Because morphologic evaluation of cells within peripheral smears is important, Dr. Hollensead says new interest exists in enhancing the review through digital computer images. CellaVision (Jupiter, FL) already offers an automated system for peripheral smear counting. The CellaVision™ DM96 is an automated image analysis system that locates and preclassifies the various types of white blood cells in peripheral blood. The analysis is performed by an artificial neural network trained on a large database of cells. The system also precharacterizes parts of the red morphology and provides functionality for platelet estimation. 1

This approach could save technologists’ time; as images already captured by the system could be viewed in a glance, Dr. Hollensead says. Atypical and/or immature cells could be sent by computer to pathologists’ homes or offices for further classification and even to off-site clinics and physicians’ offices. The visual images could also be used for teaching groups of students and conference presentations.

There is much to know regarding common white blood cell disorders. A basic understanding will help you to comprehend the bigger picture.

Reference
CellaVision™. Available at DM96http://www.cellavision.com/default.asp?groupid=2004921192025625. Accessed Dec. 1, 2004.