Introduction to hematology (Book Chapter) PDF

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GRBQ382-3667G-C01[1-10].qxd 12/12/2007 05:10 AM Page 1 Aptara(PPG Quark) Introduction and Approach to Hematology 1 Pablo Ramirez INTRODUCTION Hematologic diseases are a heterogeneous group of diseases that can have multiple clinical and laboratory manifestations that mimic nonhematologic diseases. F...

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Introduction and Approach to Hematology

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Pablo Ramirez

INTRODUCTION Hematologic diseases are a heterogeneous group of diseases that can have multiple clinical and laboratory manifestations that mimic nonhematologic diseases. For that reason, a detailed clinical history and physical exam are essential. Frequently, laboratory tests will be necessary to confirm the clinical diagnosis. The goal of this handbook is to provide an understanding of the basic mechanisms for hematologic disorders and the initial evaluation of them. The major clinical manifestations and the usual management options for these diseases are also discussed in each chapter. A P P R O A C H T O T H E H E M AT O L O G Y P AT I E N T Hematologic disorders can be approached by identifying the primary hematologic component that is affected: RBCs, WBCs, platelets, or the coagulation system. The major abnormalities in hematology are quantitative in nature, with either excessive or deficient production of one of the hematopoietic constituents (e.g., leukemias, anemias). Qualitative abnormalities also can be inherited (e.g., sickle cell disease) or acquired. History The medical history is the first step in hematology diagnostic assessment. With simple questions we can evaluate causes of a suspected anemia, the rapid onset of a hematological neoplasia, or a genetic hematological disease. Table 1-1 offers some general questions for evaluation of a hematological disorder. Physical Exam The physical exam is also an important part of the diagnostic process. Along with the history, it can suggest a diagnosis, guide lab testing, and aid in the differential diagnosis. Table 1-2 offers some general physical exam findings that are useful in the hematology patient. Lab Evaluation The clinician should be comfortable using the CBC and peripheral smear to evaluate patients for possible hematologic disorders. Patients may be referred to a hematologist based on a lab abnormality that is drawn for a reason other than the diagnosis of a primary hematologic disorder. There are certain limiting values in hematology that can help exclude or confirm the need for further testing or warn us of the possibility of potential physiological consequences (see Table 1-3). 1

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TABLE 1-1

PERTINENT HISTORY IN THE HEMATOLOGY PATIENT

Pertinent Medical History History of present illness Recent infections Fever, chills, rigors Antibiotic use Bleeding Hemorrhage, epistaxis, bleeding gums, petechiae, ecchymosis, menorrhagia Hemarthrosis Skin coloration Pallor Jaundice Dyspnea, chest pain, orthostasis Pica Abdominal fullness, early satiety Alcoholism, poor nutrition, vegetarianism Neurologic Headache, neurologic deficits Pruritus Medical history Prior malignancies, chemotherapy HIV risk factors Previous hepatitis Pregnancy Venous thrombosis Family history Bleeding disorders Anemia (African American, Mediterranean, Asian)

Hematologic Differential Diagnosis

Leukemias, lymphomas, multiple myeloma Hemolysis Thrombocytopenia, leukemias, coagulation disorder Clotting factor deficiency Anemia Hemolysis Anemia Iron deficiency Splenomegaly Megaloblastic anemia

Leukostasis, thrombocytopenia, thrombosis, Waldenström’s macroglobulinemia Polycythemia, Hodgkin’s disease Secondary malignancies (leukemia), myelodysplasia Anemia, thrombocytopenia Anemia, cryoglobulinemia Anemia, HELLP syndrome Thrombophilia Hemophilias, von Willebrand disease Hemoglobinopathies

HELLP, hemolysis, elevated liver enzymes, and low platelet count.

THE PERIPHERAL SMEAR The visual study of peripheral blood is necessary to diagnose hematologic and nonhematologic diseases. The peripheral smear obtained allows the study of the different cellular components of the blood and the determination of anomalies in red blood cells, leukocytes, and platelets affected directly by a hematologic disease or as a manifestation of other nonhematologic diseases. Moreover, there are some cases where the suspected disease makes the smear obligatory, such as thrombotic thrombocytopenic purpura and malaria. In these cases, as in others, automated hematology analyzers are able to provide a large

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The Peripheral Smear

TABLE 1-2

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PHYSICAL EXAM IN THE HEMATOLOGY PATIENT

Pertinent Exam Findings Hematologic Differential Diagnosis HEENT Anemia Conjunctival or mucosal pallor Hemolysis, hyperbilirubinemia Jaundice Conjunctival or mucosal petechiae Thrombocytopenia Iron deficiency, vitamin B12 deficiency Glossitis Lymphoma Lymphadenopathy Skin/nails Anemia Pallor Hyperbilirubinemia Jaundice Hemochromatosis Bronze appearance Iron deficiency Spoon nails (koilonychia) Thrombocytopenia Ecchymosis, petechiae Mycosis fungoides Erythematous, indurated plaques Cardiovascular Severe anemia with high-output cardiac Tachycardia, S4, prominent failure post-MI Abdominal Hairy cell or other leukemias, polycythemia, Splenomegaly lymphomas Megaloblastic anemia Neurologic Loss of vibratory sense and proprioception (dorsal and lateral columns) Musculoskeletal Multiple myeloma Bone pain/tenderness HEENT, head, ears, eyes, nose, and throat.

number of data regarding all the blood cells but will not be able to detect subtle anomalies critical in the diagnosis. Preparation Slides for a peripheral smear are typically prepared either by automated methods or by qualified technicians in a specialized laboratory. This step is critical since poorly processed samples can lead to incorrect diagnoses. Smears may be prepared on glass slides or coverslips. Ideally, blood smears should be prepared from uncoagulated blood and from a sample collected from a finger-stick. In practice, most slides are prepared from blood samples containing anticoagulants and are thus prone to the introduction of morphological artifacts. Blood smears are normally stained using Wright or May-Grünwald-Giemsa stain. Examination Examination of the smear should proceed systematically and begin under low power to identify a portion of the slide with optimal cellular distribution and staining, which normally corresponds to the thinner edge of the sample. As a general rule, the analysis starts with RBCs, continues with leukocytes, and finishes with platelets.

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TABLE 1-3

DECISION LIMITING VALUES FOR COMMON HEMATOLOGIC TESTS

Diagnostic Test

Limiting Value

Comment

Hgb

5 g/dL

Transfusion indicated even in absence of symptoms Anemia workup indicated Urgent phlebotomy indicated Risk of spontaneous bleeding Risk of bleeding increased with surgery/trauma Risk of thrombosis

10 g/dL Hct

70%

Platelet count

10,000/mm3 50,000/mm3

Neutrophil count Blast count (acute myeloblastic leukemia) Prothrombin time

500,000 to 1,000,000/mm3 2,000,000/mm3 500/mm3 100,000/mm3 1.5 control 2.5 control

Partial prothrombin Time

1.5 control 2.5 control (90 s)

Bleeding time

20 min

Antithrombin III

50% normal level

Risk of bleeding Greatest risk of infection Risk of leukostasis; urgent treatment indicated No increased bleeding risk Risk of spontaneous bleeding No increased bleeding risk Risk of spontaneous bleeding Possible risk of spontaneous bleeding Risk of spontaneous thrombosis

Under low power (10 to 20) it is possible to analyze general characteristics of RBCs to discover, for example, the presence of Rouleaux associated with multiple myeloma, estimate the WBC and platelet counts, and determine the presence of abnormal populations of cells, such as blasts, by scanning over the entire smear. Under high power (100), each of the cell lineages is examined for any abnormalities in number or morphology. Red Blood Cells Quantitative analysis of RBCs is difficult on a peripheral smear. Automated analyzers are used to calculate: MCHC, the mean cell Hgb concentration, expressed as grams per deciliter; MCH, the mean corpuscular Hgb, expressed as picograms; and MCV, the mean corpuscular volume, expressed as femtoliters (1015 L).

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The Peripheral Smear

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Qualitative analysis of RBCs should demonstrate uniform round cells with smooth membranes and a pale central area with a round rim of red Hgb. Variations in size are called anisocytosis, and variations in shape, poikilocytosis. RBC Abnormalities

[AU1]

• Hypochromia: Hypocromia corresponds to a very thin rim of Hgb and a larger central pale area. These red cells are often microcytic and are seen in iron deficiency, thalassemias, and sideroblastic anemia. • Microcytosis (6 m): Differential diagnosis includes iron-deficiency anemia, anemia in chronic disease, thalassemias, and sideroblastic anemia. These cells are usually hypochromic and have prominent central pallor. • Macrocytosis (9 m in diameter): Differential diagnosis includes liver disease, alcoholism, aplastic anemia, and myelodysplasia. Megaloblastic anemias (B12 and folate deficiencies) have macro-ovalocytes (large oval cells). Reticulocytes are large immature red cells with polychromatophilia. • Schistocytes (fragmented cells): Schistocytes are caused by mechanical disruption of cells in the microvasculature by fibrin strands or by mechanical prosthetic heart valves. Differential diagnosis includes thrombotic thrombocytopenic purpura/ hemolytic uremic syndrome, disseminated intravascular coagulation, hemolysis/ elevated liver enzymes/low platelet count (HELLP) syndrome, and malignant hypertension. • Acanthocytes (spiculated cells with irregular projections of varying length): These are seen in liver disease. • Crenated cells (cells with short, evenly spaced cytoplasmic projections): Crenated cells may be an artifact of slide preparation or found in renal failure and uremia. • Bite cells (cells with a smooth semicircle extracted): Bite cells are due to spleen phagocytes that have removed Heinz bodies consisting of denatured Hgb. They are found in hemolytic anemia due to glucose-6-phosphate dehydrogenase deficiency. • Spherocytes (round, dense cells with absent central pallor): Spherocytes are seen in immune hemolytic anemia and hereditary spherocytosis. • Sickle cells (sickle-shaped cells): Sickle cells are due to polymerization of Hgb S. They are found in sickle cell disease as well as SC disease but not in sickle cell trait. • Target cells (cells with extra Hgb in the center surrounded by a rim of pallor; bull’s-eye appearance): Target cells are due to an increase in the ratio of cell membrane surface area to Hgb volume within the cell. These have a central spot of Hgb surrounded by a ring of pallor from the redundancy in cell membrane. They are found in liver disease, postsplenectomy, in hemoglobinopathies, and in thalassemia. • Teardrop cells/dacryocytes (teardrop-shaped cells): These are found in myelofibrosis and myelophthisic states of marrow infiltration. • Ovalocytes (elliptical cells). Ovalocytes are due to the abnormal membrane cytoskeleton found in hereditary elliptocytosis. • Polychromatophilia (blue hue of cytoplasm): This is due to the presence of RNA and ribosomes in reticulocytes. • Howell-Jolly bodies (small, single, purple cytoplasmic inclusions): These represent nuclear remnant DNA and are found after splenectomy or with functional asplenism. • Basophilic stippling (dark-purple inclusions, usually multiple): Basophilic stippling arises from precipitated RNA found in lead poisoning and thalassemia. • Nucleated red cells: These are not normally found in peripheral blood. They appear in hypoxemia and myelofibrosis or other myelophthisic conditions, as well as with severe hemolysis.

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• Heinz bodies (inclusions seen only on staining with violet crystal): Heinz bodies represent denatured Hgb and are found in glucose-6-phosphate dehydrogenase after oxidative stress. • Parasites: A variety of parasites, including malaria and babesiosis, may be seen within red cells. • Rouleaux (red cell aggregates resembling a stack of coins): Rouleaux is due to the loss of normal electrostatic charge-repelling red cells due to coating with abnormal paraprotein, such as in multiple myeloma. • Leukoerythroblastic smear (teardrop cells, nucleated red cells, and immature white cells): This is found in marrow infiltration or fibrosis (myelophthisic conditions). White Blood Cells WBCs normally seen on the peripheral smear include mature granulocytes (neutrophils, eosinophils, and basophils) and mature agranulocytes (lymphocytes and monocytes). Under normal conditions immature myeloid and lymphoid cells are not seen and their presence is related to conditions such as infections and hematologic neoplasias. • Neutrophils: Neutrophils comprise 55% to 60% of total WBCs (1.8  109 to 7.7  109/L, or thousands per cubic millimeter). They have nuclei containing three or four lobes and granular cytoplasm. The normal size is 10 to 15 m. Hypersegmented neutrophils contain more than five lobes and are found in megaloblastic anemias. The cytoplasmatic granules correspond to enzymes that are used during the acute phase of inflammation. Increased prominence of cytoplasmic granules is indicative of systemic infection or therapy with growth factors and is known as toxic granulation. Neutrophils develop from myeloblasts through promyelocyte, myelocyte, metamyelocyte, and band forms and progress to mature neutrophils. Only mature neutrophils and bands are normally found in peripheral blood. Metamyelocytes and myelocytes may be found in pregnancy, infections, and leukemoid reactions. The presence of less mature forms in the peripheral blood is indicative of hematologic malignancy or myelophthisis. • Lymphocytes: Lymphocytes comprise 25% to 35% (1  109 to 4.8  109/L, or thousands per cubic millimeter) of total WBCs. They contain a dark, clumped nucleus and a scant rim of blue cytoplasm. The differentiation of T and B cells is very difficult using light microscopy. The normal size is 7 to 18 m. Atypical (or reactive) lymphocytes seen in viral infections contain more extensive, malleable cytoplasm that may encompass surrounding red cells. • Eosinophils: Eosinophils comprise 0.5% to 4% of total WBCs (0.2  109/L, or thousands per cubic millimeter). These are large cells containing prominent red/orange granules and a bilobed nucleus. The normal size is 10 to 15 m. Increased numbers are found in parasitic infections and allergic disorders. • Monocytes: Monocytes comprise 4% to 8% of total WBCs (0  109 to 0.3  109/L, or thousands per cubic millimeter). These are the bigger circulating cells with an eccentric U-shaped nucleus. They contain blue cytoplasm and are the precursors of the mononuclear phagocyte system (macrophages, osteoclasts, alveolar macrophages, Kupfer cells, and microglia). The usual size is 12 to 20 m. • Basophils comprise 0.01% to 0.3% of total WBCs (0 to 0.1  109/L, or thousands per cubic millimeter). Their cytoplasm contains large dark-blue granules and a

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Bone Marrow Evaluation

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bilobed nucleus. They are involved in inflammation reactions and increased numbers are also seen in chronic myeloid leukemia. As for eosinophils, the normal size is 10 to 15 m. WBC Abnormalities Quantitative anomalies result in leukopenia and leukocytosis. Main causes of leukopenia include bone marrow failure (aplastic anemia), myelophthisis (acute leukemia), drugs (immunosuppressive drugs, propylthiouracil), and hypersplenism (portal hypertension). Main causes of leukocytosis are infection, inflammation, malignancies, and allergic reactions. • Pelger-Huet anomaly (neutrophils have a bilobed nucleus connected by a thin strand and decreased granulation): This anomaly is seen in myelodysplastic syndromes. • Hypersegmented neutrophils (more than nuclear lobes): These are found in megaloblastic anemias (vitamin B12 and folate deficiency). • Blast cells (myeloblasts or lymphoblasts; large cells with large nuclei and prominent nucleoli): Blast cells are seen in acute leukemia. • Auer rods (rodlike granules in blast cytoplasm): Auer rods are pathognomonic for acute myelogenous leukemia, especially acute promyelocytic leukemia (M3). • Hairy cells (lymphoid cells with ragged cytoplasm): These are seen in hairy cell leukemia. • Sézary cells (atypical lymphoid cells with cerebriform nuclei): Sézary cells are seen in cutaneous T cell lymphoma. Platelets Platelets appear as small (1- to 2-m-diameter), purplish cytoplasmic fragments without a nucleus, containing red/blue granules. Derived from bone marrow giant cells called megakaryocytes, they are involved in the cellular mechanisms of primary hemostasis leading to the formation of blood clots. Normal counts are 150,000 to 400,000 per cubic millimeter of peripheral blood (150  109 to 400  109/L). The number of platelets per high-power field multiplied by 20,000 usually estimates the platelet count per microliter. Alternatively, one should find 1 platelet for every 10 to 20 red cells. Numbers of platelets can decrease due to bone marrow disease (myelophthisic bone marrow), consumption (disseminated intravascular coagulation), or drugs. An increase in numbers can be seen in bone marrow overproduction (myeloproliferative syndromes) or is a normal response to massive bleeding. Pseudo-thrombocytopenia represents clumping of platelets in blood samples collected in EDTA, resulting in spuriously low platelet counts. This phenomenon can be avoided by using citrate to anticoagulate blood samples sent for blood counts. B O N E M A R R O W E V A L U AT I O N Introduction For many hematologic diseases that affect the bone marrow, evaluation of the peripheral blood smear does not provide sufficient information, and a direct examination of the bone marrow is required to establish the diagnosis. The bone marrow biopsy can be done at the bedside under local anesthesia, although some patients may require low doses of anxiolytics or opioids for the procedure. Despite advances in the bone marrow biopsy and aspiration techniques, they are still commonly considered painful procedures by patients and

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some physicians, but with expertise, both can be performed safely and with minimal discomfort to the patient. Indications and Contraindications The most common indications for bone marrow evaluation are workup of bone marrow malignancies, staging of marrow involvement by metastatic tumors, assessment of infectious diseases that may involve the bone marrow (i.e., HIV, tuberculosis), determination of marrow damage in patients exposed to radiation, drugs, and chemicals, and workup of metabolic storage diseases. There are a few absolute contraindications for the procedure, including infection, previous radiation therapy at the site of biopsy, and poor patient cooperation. Thrombocytopenia is not a contraindication to bone marrow biopsy, although it may be associated with more procedure-related bleeding. Patients who have a coagulopathy require factor replacement or withholding of anticoagulation to minimize bleeding complications. Technique In adults, the most common places to do the procedure are the posterior and anterior iliac crests, which are accessible and safe locations of active hematopoiesis. Othe...