- 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
- Morphological classification (Table 1.1): it is based on:
- Red cell size (normocytic, microcytic, or macrocytic), and
- Degree of hemoglobinization (normochromic or hypochromic).
- Etiological classification: The etiological classification of anemia is listed in Table 1.2.
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:
- 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.
- 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 pgMCH = Hb (in g/L)/RBC (in millions/μL) = 15 × 10/5 = 30 pg
- 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
- 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.
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.
- Hemoglobin and hematocrit (PCV): decreased
- Red cell indices:
- Reticulocyte count: low for the degree of anemia.
Fig. 1.2: Diagrammatic appearance of peripheral blood smear with microcytic hypochromic red blood cells
Serum Iron Profile (Table 1.4)
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.
Diminished tissue enzymes cause characteristic epithelial changes of iron deficiency anemia.
- Angular stomatitis and glossitis
- Chronic atrophic gastritis
- Koilonychia (spoon nails)
Causes of Microcytic Hypochromic Anemia
- Iron deficiency anemia
- Thalassemia major
- Anemia of chronic disorders
- Others: alcohol, lead poisoning and drugs
- Sideroblastic anemia (rare cause).
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)
Pathogenesis of Megaloblastic Change
- 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.
- Delayed maturation of nucleus. The nuclear maturation lags behind the cytoplasmic maturation and results in abnormally large nucleated erythroid precursors named as megaloblasts.
- Cytoplasm matures normally. RBCs are larger than normal → macrocytes.
- Affects all rapidly dividing cells of the body (including skin, GI tract, and bone marrow).
- Ineffective erythropoiesis: megaloblast precursors undergo intramedullary destruction.
Laboratory Findings of Megaloblastic Anemia
Blood findings in vitamin B12 and/or folic acid deficiency are similar.
- Hemoglobin and hematocrit (PCV): reduced
- Red cell indices
- Reticulocyte count: normal or low.
- Combined vitamin B12/folic acid and iron deficiency.
- Peripheral smear shows two populations of RBCs namely: macro-ovalocytes and microcytic hypochromic (Fig. 1.5).
Fig. 1.3: Peripheral blood smear showing macro-ovalocytes (arrows) and hypersegmented neutrophil (inset)
Fig. 1.4: Diagrammatic peripheral blood smear showing macro-ovalocytes (thick arrows) and hypersegmented neutrophil (thin arrow)
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
Fig. 1.6: Bone marrow aspirate showing megaloblastic precursors (arrows) in varying stages of maturation (inset shows early megaloblast)
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.
Diagnostic tests for vitamin B12 deficiency
- Serum vitamin B12 levels: decreased
- 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 (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).
- An autoimmune disease due to destruction of gastric mucosa.
- Stomach shows damage to parietal cells, dense infiltration by lymphocytes and plasma cells → chronic atrophic gastritis → failure 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.
- Atrophic glossitis: tongue shiny, glazed and beefy.
- 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.
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.
Hematopoietic stem cell (HSC) disorder characterized by:
- Pancytopenia (anemia, neutropenia and thrombocytopenia)
- With markedly hypocellular bone marrow (less than 30% cellularity).
The most common causes associated with aplastic anemia are shown in Table 1.7.
Pathogenesis (Fig. 1.9)
- Any age of both sexes
- Progressive weakness, pallor and dyspnea due to anemia
- Frequent (mucocutaneous bacterial infections) or fatal infections due to neutropenia
- Bleeding manifestations in the form of petechiae, bruises and ecchymoses due to thrombocytopenia.
Diagnosis: diagnosis is made with peripheral blood and bone marrow biopsy findings.
- Should be distinguished from other causes of pancytopenia (Table 1.8)