Rapid Review of Hematology Ramadas Nayak, Sharada Rai
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1Disorders of Red Cells2

Anemias of Impaired Red Cell ProductionCHAPTER 1

 
ANEMIA
 
Definition
  • Decrease below normal of the hemoglobin concentration (Hb)/RBC count/hematocrit (packed cell volume).
  • Reduction of the total circulating red cell mass below normal limits.
  • Decrease in the oxygen-carrying capacity of the blood, which leads to tissue hypoxia.
Anemia may be absolute (decreased RBC mass), or relative (associated with a higher plasma volume). Anemia is conventionally used for absolute anemia.
 
Classification of Anemia
  1. Morphological classification (Table 1.1): it is based on:
    1. Red cell size (normocytic, microcytic, or macrocytic), and
    2. Degree of hemoglobinization (normochromic or hypochromic).
    TABLE 1.1   Morphological classification of anemia
    Type of anemia
    Microcytic hypochromic
    Normocytic normochromic
    Macrocytic
    Size of RBCs
    Smaller than normal
    Normal
    Larger than normal
    Central pallor in RBCs
    More than 1/3
    Normal
    Normal
    Mean corpuscular volume (MCV)
    Reduced (< 80 fL)
    Normal (82–98 fL)
    Increased (>100 fL)
    Mean corpuscular hemoglobin concentration (MCHC)
    Reduced (< 30 g/dL)
    Normal (31–36 g/dL)
    Normal (31–36 g/dL)
    Examples
    Iron deficiency anemia, thalassemia
    During blood loss, anemia of chronic diseases
    Deficiency of vitamin B12 and folic acid
    Morphology of RBC
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  2. Etiological classification: The etiological classification of anemia is listed in Table 1.2.
TABLE 1.2   Etiological classification of anemia
1. IMPAIRED RED CELL PRODUCTION
  • Disturbed Proliferation and Maturation of Erythroblasts
  • Defective DNA synthesis
    • Megaloblastic anemias due to deficiency or impaired utilization of vitamin B12 and folic acid
    • Anemia of renal failure due to deficiency of erythropoietin
    • Anemia of chronic disease due to iron sequestration and relative erythropoietin deficiency
    • Anemias of endocrine disorders
  • Defective hemoglobin synthesis
    • Defective heme synthesis: iron deficiency, sideroblastic anemia
    • Defective globin synthesis: thalassemias
  • Marrow Replacement
  • Primary hematopoietic neoplasms: acute leukemia, myelodysplastic syndromes
  • Marrow Infiltration (myelophthisic anemia)
  • Metastatic neoplasms
  • Disturbed Proliferation and Differentiation of Stem Cells
  • Aplastic anemia, pure red cell aplasia
2. INCREASED RED CELL DESTRUCTION (HEMOLYTIC ANEMIAS)
  • Intrinsic (Intracorpuscular) Abnormalities
  • Hereditary
    • Membrane abnormalities: spherocytosis, elliptocytosis
    • Enzyme deficiencies: glucose-6-phosphate dehydrogenase, pyruvate kinase
    • Disorders of hemoglobin synthesis
      • Deficient globin synthesis: thalassemia syndromes
      • Structurally abnormal globin synthesis (hemoglobinopathies): sickle cell anemia
  • Acquired
    • Membrane defects: paroxysmal nocturnal hemoglobinuria
  • Extrinsic (Extracorpuscular) Abnormalities
  • Antibody-mediated
    • Isohemagglutinins: transfusion reactions, Rh disease of the newborn
    • Autoantibodies: idiopathic (primary), drug-associated, systemic lupus erythematosus
  • Mechanical trauma to RBCs:
    • Microangiopathic hemolytic anemia: disseminated intravascular coagulation
  • Infections: malaria
3. BLOOD LOSS
  • Acute: trauma
  • Chronic: lesions of gastrointestinal tract (e.g. carcinoma colon), gynecological disturbances
 
RED CELL INDICES
Red cell indices are useful in morphological characterization and diagnosis of anemias. They are either directly measured or automatically calculated by specialized instruments. Red cell indices include:
  1. Mean Corpuscular Volume (MCV)
    • MCV is indicative of average volume of the RBC and is expressed in femtoliters (fL).
    • It is used for classification and differential diagnosis of anemias.
    • Normal range: 82–98 fL.
      5
  2. Mean Corpuscular Hemoglobin (MCH)
    • MCH indicates the amount of Hb (weight) per RBC and is expressed as picograms (1 pg = 10-12 g).
    • It is of limited value in differential diagnosis of anemias.
    • Normal range: 27–32 pg
      MCH = Hb (in g/L)/RBC (in millions/μL) = 15 × 10/5 = 30 pg
  3. Mean Corpuscular Hemoglobin Concentration (MCHC)
    • MCHC denotes the average concentration of hemoglobin in the RBC taking volume into account. It is expressed as g/dL (earlier it was expressed as %).
    • It is a better indicator of hypochromasia than MCH.
    • Normal range: 31–35 g/dL.
      MCHC = Hb (in g/dL)/PCV = 15/0.45 = 33 g/dL
  4. Red Cell Distribution Width (RDW)
    • RDW is a quantitative measure of anisocytosis.
    • Normal RDW is 11.5% to 14.5%.
    • A normal RDW indicates that RBCs are relatively uniform in size. A raised RDW indicates that red cells are heterogeneous in size and/or shape. In early iron deficiency anemia, RDW increases along with low MCV while in thalassemia trait, RDW is normal with low MCV.
      RDW = (Standard deviation ÷ mean cell volume) × 100
 
IRON DEFICIENCY ANEMIA
Iron deficiency anemia (IDA) is the most common nutritional disorder.
 
Etiology (Table 1.3)
IDA is due to deficiency of iron causing defective heme synthesis.
TABLE 1.3   Causes of iron deficiency anemia
1. Dietary deficiency/lack
  • Milk-fed infants
  • Elderly with improper diet and poor dentition
  • Low socioeconomical sections
  • Vegetarians (contains poorly absorbable inorganic iron)
2. Impaired absorption
  • Total/partial gastrectomy
  • Intestinal absorption is impaired in sprue, other causes of intestinal steatorrhea and chronic diarrhea
  • Specific items in the diet, like phytates of cereals, tannates, carbonates, oxalates, phosphates and drugs can impair iron absorption
3. Increased demand/requirement
  • Growing infants, children and adolescents
  • Pregnancy and lactation
4. Chronic blood loss: due to bleeding from the
  • Gastrointestinal tract (e.g. peptic ulcers, gastric carcinoma, colonic carcinoma, hemorrhoids, hookworm infestation or nonsteroidal anti-inflammatory drugs)
  • Urinary tract (e.g. renal or bladder tumors)
  • Genital tract (e.g. menorrhagia, uterine cancer)
  • Respiratory tract (e.g. hemoptysis)
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Pathogenesis of Iron Deficiency Anemia
It is due to decreased synthesis of heme and can be divided into 3 stages.
  • Stage 1 (Iron depletion): iron adequate to maintain normal hemoglobin level and only serum ferritin decreased.
  • Stage 2 (Iron deficient erythropoiesis): lowering of serum iron and transferrin saturation levels without anemia (Hb, MCV and MCH within normal range). Bone marrow shows iron deficient erythropoiesis.
  • Stage 3 (Iron deficiency anemia): low serum iron, serum ferritin and transferrin saturation. Impaired hemoglobin production. Morphologically, first reduction in the size (microcytic) and later increase in the central pallor (hypochromia) of RBCs.
 
Laboratory Findings
 
Peripheral Blood
  • Hemoglobin and hematocrit (PCV): decreased
  • Red cell indices:
    zoom view
  • Reticulocyte count: low for the degree of anemia.
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Fig. 1.1: Peripheral blood smear showing microcytic hypochromic red blood cells
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Fig. 1.2: Diagrammatic appearance of peripheral blood smear with microcytic hypochromic red blood cells
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Serum Iron Profile (Table 1.4)
TABLE 1.4   Serum iron profile in IDA
Normal range
Value in IDA
Observation
Serum ferritin
15–300 µg/L
<15 µg/L
Serum iron
50–150 µg/dL
10–15 µg/dL
Serum transferrin saturation
30–40%
<15%
Total plasma iron-binding capacity (TIBC)
310–340 µg/dL
350–450 µg/dL
Serum transferrin receptor (TFR)
0.57–2.8 µg/L
3.5–7.1 µg/L
Red cell protoporphyrin
30–50 µg/dL
>200 µg/dL
 
Reticulocyte Hemoglobin
It is decreased and is an early feature of IDA.
 
Clinical Features of IDA
Nonspecific and related to both severity and the cause of the anemia (e.g. gastrointestinal disease)
  • Onset: insidious.
  • Nonspecific symptoms: fatigue, palpitations, breathlessness, weakness and irritability.
  • Pharyngeal/esophageal webs formed cause dysphagia.
  • Patterson-Kelly or Plummer-Vinson syndrome:
    • Microcytic hypochromic anemia
    • Atrophic glossitis
    • Esophageal webs
  • Congestive heart failure in severe anemia.
  • Central nervous system: pica-unusual craving for substances with no nutritional value like clay or chalk. Craving for ice (pagophagia) specific to iron deficiency. Pica may be the cause rather than effect of IDA.
 
Physical Findings
Diminished tissue enzymes cause characteristic epithelial changes of iron deficiency anemia.
  • Angular stomatitis and glossitis
  • Chronic atrophic gastritis
  • Koilonychia (spoon nails)
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Causes of Microcytic Hypochromic Anemia
  • Iron deficiency anemia
  • Thalassemia major
  • Anemia of chronic disorders
  • Others: alcohol, lead poisoning and drugs
  • Sideroblastic anemia (rare cause).
 
MEGALOBLASTIC ANEMIA
Anemias characterized by defective/impaired DNA synthesis and distinct megaloblasts in the bone marrow. Megaloblastic anemias are common among anemias due to impaired red cell production.
 
Etiology of Megaloblastic Anemia (Table 1.5)
TABLE 1.5   Causes of megaloblastic anemia
VITAMIN B12 DEFICIENCY
1. Decreased Intake: inadequate diet, “pure vegetarians” (vegans)
2. Impaired Absorption
  • Gastric: deficiency of gastric acid or pepsin or intrinsic factor
    • Pernicious anemia
    • Post-gastrectomy
  • Intestinal
    • Loss of absorptive surface
      • Malabsorption syndromes
      • Diffuse intestinal disease, e.g. lymphoma, systemic sclerosis
      • Ileal resection, Crohn disease
    • Bacterial or parasitic competition for vitamin B12
      • Bacterial overgrowth in blind loops and diverticula of bowel
      • Fish tapeworm infestation
3. Increased Demand: pregnancy, hyperthyroidism, disseminated cancer
FOLIC ACID DEFICIENCY
1. Decreased Intake: inadequate diet—alcoholism, malnutrition
2. Impaired Absorption
  • Malabsorption states: nontropical and tropical sprue
  • Diffuse infiltrative diseases of the small intestine (e.g. lymphoma)
  • Drugs: anticonvulsant phenytoin and oral contraceptives
3. Increased Loss: hemodialysis
4. Increased Demand: pregnancy, infancy, disseminated cancer, markedly increased hematopoiesis
5. Impaired Utilization: folic acid antagonists, such as methotrexate
 
Pathogenesis of Megaloblastic Change
  1. Impaired DNA synthesis: megaloblastic anemia is commonly due to deficiency of vitamin B12 (cyanocobalamin) or folic acid. Both are required for the synthesis of DNA.
    1. Delayed maturation of nucleus. The nuclear maturation lags behind the cytoplasmic maturation and results in abnormally large nucleated erythroid precursors named as megaloblasts.
    2. Cytoplasm matures normally. RBCs are larger than normal → macrocytes.
    3. Affects all rapidly dividing cells of the body (including skin, GI tract, and bone marrow).
  2. Ineffective erythropoiesis: megaloblast precursors undergo intramedullary destruction.
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Laboratory Findings of Megaloblastic Anemia
Blood findings in vitamin B12 and/or folic acid deficiency are similar.
 
Peripheral Blood
  • Hemoglobin and hematocrit (PCV): reduced
  • Red cell indices
    zoom view
  • Reticulocyte count: normal or low.
 
Dimorphic Anemia
  • Combined vitamin B12/folic acid and iron deficiency.
  • Peripheral smear shows two populations of RBCs namely: macro-ovalocytes and microcytic hypochromic (Fig. 1.5).
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Fig. 1.3: Peripheral blood smear showing macro-ovalocytes (arrows) and hypersegmented neutrophil (inset)
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Fig. 1.4: Diagrammatic peripheral blood smear showing macro-ovalocytes (thick arrows) and hypersegmented neutrophil (thin arrow)
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Fig. 1.5: Diagrammatic peripheral blood smear of dimorphic anemia showing macro-ovalocytes and microcytes
The differences between normoblasts and megaloblasts are shown in Table 1.6
TABLE 1.6   Differences between normoblast and megaloblast
Characteristics
Normoblast
Megaloblast
Cell size
Normal
Larger than corresponding normoblast
Nuclear chromatin
Normal
Open sieve-like
Nuclear maturation
Normal
Lags behind cytoplasmic maturation
Mitosis
Normal
Increased and abnormal
Maturation in bone marrow
Normal (Late > intermediate > early normoblast)
Increased proportion of more primitive erythroid cells (Late < intermediate < early megaloblast)
Evidence of dyserythropoiesis
Absent
Present (irregular nuclei, Howell Jolly bodies)
Myelopoiesis
Normal
Shows giant metamyelocytes
Found in
Normal bone marrow
Bone marrow of megaloblastic anemia
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zoom view
Fig. 1.6: Bone marrow aspirate showing megaloblastic precursors (arrows) in varying stages of maturation (inset shows early megaloblast)
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Fig. 1.7: Diagrammatic picture of bone marrow aspirate showing megaloblastic precursors (thick arrows) in varying stages of maturation
 
Biochemical Tests for Megaloblastic Anemia
 
Common for both vitamin B12 and folic acid deficiency
Deoxyuridine suppression test: it is a sensitive measure of deficiency of 5, 10-methylene THF, which occurs in both folic acid and vitamin B12 deficiency.
zoom view
 
Diagnostic tests for vitamin B12 deficiency
  • Serum vitamin B12 levels: decreased
    zoom view
  • Schilling test for vitamin B12 absorption (Refer ).
 
Specific tests for folic acid deficiency
  • Serum folic acid levels: decreased
  • FIGLU in urine: excessively excreted.
 
PERNICIOUS ANEMIA
Pernicious anemia (PA) is an autoimmune disease due to deficiency of intrinsic factor causing impaired absorption of vitamin B12 and megaloblastic anemia.
Rare in India. A genetic predisposition is suspected.
Age: older age—fifth to eighth decades of life
Sex: females are more involved than males (F: M is 1.5: 1).
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Etiopathogenesis
  • An autoimmune disease due to destruction of gastric mucosa.
  • Stomach shows damage to parietal cells, dense infiltration by lymphocytes and plasma cells → chronic atrophic gastritisfailure of production of intrinsic factor.
  • Presence of autoantibodies: two major types of autoantibodies—
    • Anti-intrinsic factor (IF) antibody
      • Type I (blocking) antibody: blocks the binding of vitamin B12 to IF. Present in 50–75% of the cases.
      • Type II (binding) antibody: attaches to the IF–vitamin B12 complex and prevent its binding to receptors in the ileum. Present in about 40% of patients.
    • Parietal cell (Type III) antibody: neither specific for PA nor other autoimmune disorders. It is found in 90% of patients.
 
Morphology
 
Alimentary System
  • Atrophic glossitis: tongue shiny, glazed and beefy.
  • Stomach:
    • Diffuse chronic atrophic gastritis and impaired secretion of hydrochloric acid, pepsin and intrinsic factor.
      • Histologically atrophy of the glands, with loss of both chief cells and parietal cells.
      • Nuclei of mucosal cells look similar to that of megaloblasts.
      • Dense infiltration by lymphocytes and plasma cells.
    • Intestinal metaplasia.
 
Central Nervous System
Found in 75% of cases.
  • Demyelination in the dorsal and lateral tracts: subacute combined degeneration
  • Peripheral neuropathy.
 
Laboratory Findings (Fig. 1.8)
Blood, bone marrow and biochemical test findings are similar to those described earlier for megaloblastic anemias (Refer to ).
 
Specific Diagnostic Tests for Pernicious Anemia
  • Schilling test for vitamin B12 absorption: abnormal
    • Radioactive vitamin B12 is used to assess the status of intrinsic factor (IF) and vitamin B12.
    • Helps in distinguishing megaloblastic anemia due to IF deficiency (pernicious anemia) from other causes of vitamin B12 deficiency.
  • Serum antibodies to intrinsic factor are highly specific for pernicious anemia
  • Achlorhydria with histamine/pentagastrin stimulation.
  • Severe deficiency of intrinsic factor.
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zoom view
Fig. 1.8: Clinical features and laboratory findings in pernicious anemia
 
Clinical Features of Megaloblastic Anemia
The clinical features of vitamin B12 deficiency anemia and pernicious anemia are:
  • Onset: insidious and progresses slowly.
  • Classic triad of presentation: weakness, sore throat and paresthesias.
  • Tongue: painful red “beefy” tongue.
  • Neurological manifestations:
    • Bilateral peripheral neuropathy: glove and sock distribution of numbness or paresthesia
    • Demyelination of spinal cord: subacute combined demyelination/degeneration of dorsal and lateral tracts—ataxia, uncoordinated gait, impairment of vibration and position sense.
  • Atherosclerosis: serum homocysteine level is raised and is a risk factor for atherosclerosis and thrombosis.
 
APLASTIC ANEMIA
Hematopoietic stem cell (HSC) disorder characterized by:
  • Pancytopenia (anemia, neutropenia and thrombocytopenia)
  • With markedly hypocellular bone marrow (less than 30% cellularity).
 
Etiology
The most common causes associated with aplastic anemia are shown in Table 1.7.14
TABLE 1.7   Common causes of aplastic anemia
1. ACQUIRED
  • Idiopathic
  • Acquired defects in stem cell
  • Immune mediated
  • Secondary
  • Chemical Agents
  • Cytotoxic drugs: alkylating agents, antimetabolites
  • Inorganic arsenicals
  • Benzene
  • Chloramphenicol
  • Idiosyncratic
  • Chloramphenicol
  • Penicillamine
  • Gold salts
  • Methylphenylethyl hydantoin
  • Phenylbutazone
  • Carbamazepine
  • Organic arsenicals
  • Physical Agents: whole-body irradiation
  • Viral Infections: hepatitis virus, Epstein-Barr virus, cytomegalovirus, herpes zoster (Varicella zoster), HIV
2. INHERITED: fanconi anemia, telomerase defects
 
Pathogenesis (Fig. 1.9)
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Fig. 1.9: Pathogenesis of aplastic anemia
 
Clinical Features
  • Any age of both sexes
  • Insidious
    • Progressive weakness, pallor and dyspnea due to anemia
    • Frequent (mucocutaneous bacterial infections) or fatal infections due to neutropenia
      15
    • Bleeding manifestations in the form of petechiae, bruises and ecchymoses due to thrombocytopenia.
 
Laboratory Findings
 
Peripheral Blood
zoom view
 
No Splenomegaly
Diagnosis: diagnosis is made with peripheral blood and bone marrow biopsy findings.
 
Differential Diagnosis
  • Should be distinguished from other causes of pancytopenia (Table 1.8)
TABLE 1.8   Causes of pancytopenia
Decreased bone marrow function
• Aplastic anemia
  • Idiopathic
  • Secondary
  • Inherited
• Myelodysplastic syndromes
• Bone marrow infiltration with
  • Leukemia
  • Lymphoma
  • Myeloma
  • Tumors (carcinoma)
  • Granulomatous diseases (e.g. tuberculosis, sarcoidosis)
• Nutritional deficiencies:
  • Megaloblastic anemia (vitamin B12 and folic acid deficiency)
• Paroxysmal nocturnal hemoglobinuria
• Myelofibrosis (rare)
• Hemophagocytic syndrome
Increased peripheral destruction
• Hypersplenism
Prognosis: unpredictable.