Red Blood Cell Disorders

Chapter 11 Red Blood Cell Disorders

• Erythropoiesis refers to the production of RBCs in the bone marrow and is dependent on the release of erythropoietin from the kidneys.

A. Erythropoiesis and erythropoietin (EPO)

1. Primarily synthesized in the renal cortex by interstitial cells in the peritubular capillary bed

EPO: synthesized by interstitial cells in peritubular capillary bed

2. Stimuli for EPO release

Stimuli for EPO: hypoxemia, left-shifted OBC, high altitude

• Hypoxemia, severe anemia, left-shifted O₂-binding curve (OBC), high altitude

3. Increased O₂ content suppresses EPO release (e.g., polycythemia vera).

EPO increases the O₂-carrying capacity of blood by stimulating erythroid stem cells to divide. Epoetin alfa, a form of EPO produced by recombinant DNA technology, is frequently abused by athletes to increase their energy level. It also is used in the treatment of anemia associated with renal failure, chronic disease, and chemotherapy.

4. Other sources of EPO

• Ectopic production by renal cell carcinoma and hepatocellular carcinoma

5. Peripheral blood markers of erythropoiesis

a. Reticulocytes are newly released RBCs from the bone marrow.

b. Identified with supravital stains

• Detect thread-like RNA filaments in the cytoplasm (Fig. 11-1)

c. In 24 hours, they become mature RBCs.

B. Reticulocyte count

1. Marker of effective erythropoiesis

11-1 Peripheral blood reticulocytes with supravital stain (new methylene blue). Red blood cells with thread-like material in the cytosol represent residual RNA filaments and protein (arrow).

(From Hoffbrand AV: Color Atlas: Clinical Hematology, 3rd ed. St. Louis, Mosby, 2000, Fig. 1-43B.)

Reticulocyte count: measure of effective erythropoiesis

• Bone marrow response to anemia

2. Develop into a mature RBC in 24 hours

• Maturation occurs with the help of splenic macrophages.

3. Reticulocyte count is reported as a percentage (normal < 3%).

a. Percentage count is falsely increased in anemia (Fig. 11-2).

11-2 Correction of the reticulocyte count for degree of anemia. Note that the normal reticulocyte count is 3% when 3 reticulocytes (pale blue RBCs) are expressed as a percentage of 100 RBCs (red blood cells) in the microscopic field. However, the same 3 reticulocytes account for 10% of the RBCs in the patient with anemia, who has only 30 RBCs in the microscopic field.

(From Goljan EF, Sloka KI: Rapid Review Laboratory Testing in Clinical Medicine. St. Louis, Mosby Elsevier, 2008, p 146, Fig. 5-3.)

Reticulocyte count: must correct for degree of anemia.

b. Initial percentage must be corrected for the degree of anemia.

c. Corrected reticulocyte count = (actual Hct/45) × reticulocyte count, where 45 represents the normal hematocrit (Hct)

Correction: Hct/45 × reticulocyte count

d. Example

(1) Hct 15%, reticulocyte count 18%

(2) Corrected reticulocyte count is 6% (15/45 × 18% = 6%)

e. Additional correction is required if RBC polychromasia is present.

Polychromasia: divide original correction by 2

(1) Polychromatic RBCs are even younger RBCs than reticulocytes (Fig. 11-3).

(2) Appear when there is a very brisk hemolytic anemia

(3) Require 2 to 3 days before becoming mature RBCs

(4) Falsely increase the initial reticulocyte count, because they have RNA filaments and are counted as reticulocytes

(5) Correction is made by dividing the initial reticulocyte count corrected for the degree of anemia by 2.

• In the above example, if polychromasia was present, the additional correction would be 6%/2 = 3%, which is still a good response to anemia.

5. Corrected reticulocyte count < 3%

a. Poor bone marrow response to anemia (i.e., ineffective erythropoiesis)

b. Examples—untreated iron deficiency; aplastic anemia

C. Extramedullary hematopoiesis (EMH)

• RBC, WBC, and platelet production that occurs outside the bone marrow

1. Common sites of EMH are the liver and spleen.

EMH: most often occurs in the liver and spleen

2. Pathogenesis

a. Intrinsic bone marrow disease (e.g., myelofibrosis)

b. Accelerated erythropoiesis (e.g., severe hemolysis in sickle cell disease)

(1) Expands the bone marrow cavity

(2) Radiograph of the skull shows a “hair-on-end” appearance (Fig. 11-4).

3. EMH produces hepatosplenomegaly.

11-4 Skull radiograph showing “hair-on-end” due to expansion of the bone marrow cavity from accelerated erythropoiesis (e.g., severe hemolysis in sickle cell disease).

(From Bouloux P: Self-Assessment Picture Tests: Medicine, Vol. 1. London, Mosby-Wolfe, 1997, p 49, Fig. 97.)

EMH: hepatosplenomegaly

In the fetus, hematopoiesis (blood cell formation) begins in the yolk sac and subsequently moves to the liver and finally the bone marrow by the fifth to sixth months of gestation

II. Complete Blood Cell Count (CBC) and Other Studies

A. Components of a CBC

1. Hemoglobin (Hb), Hct, RBC count

2. RBC indices, RBC distribution width (RDW)

3. WBC count with a differential count, platelet count

4. Evaluation of the peripheral blood morphology

B. Hb, Hct, and RBC counts

1. Factors affecting the normal range (reference interval)

a. Premature newborns

(1) Variable Hb concentration depending on gestational age

(2) Anemia in prematurity

Anemia prematurity: loss of iron from mother; blood loss from venipuncture

(a) Iron deficiency

• Due to loss of the daily supply of iron from mother’s iron stores

(b) Blood loss from excessive venipunctures

b. Newborns

(1) Newborns have higher normal ranges than do infants and children.

(2) HbF (2α/2γ globin chains) shifts the OBC to the left causing the release of EPO.

• EPO causes an increase in Hb, Hct, and RBC count.

Fetal Hb: left-shifts OBC causing an increase in Hb

(3) After birth, the Hb drops from ∼︀18.5 to 11 g/dL (physiologic anemia).

Fetal RBCs containing HbF are destroyed by splenic macrophages over the ensuing 6 to 9 months. The unconjugated bilirubin derived from the initial destruction of fetal RBCs is responsible for physiologic jaundice of the newborn, which occurs ∼︀3 days from birth.

(4) HbF-containing cells are replaced by RBCs containing HbA (>97%), HbA₂ (<2.5%), and HbF (<1%).

c. Children

(1) Have a lower Hb concentration than adults (anemia <11.5 g/dL)

Children: more right-shifted OBCs than adults

Anemia in children: <11.5 g/dL

(2) Due to higher serum phosphorus levels

(a) Increased serum phosphorus increases synthesis of 2,3-bisphosphoglycerate (BPG).

(b) Increased 2,3-BPG right-shifts the OBC.

d. Adult men and women

(1) Men have higher Hb levels than women.

Anemia in adult male: <13.5 g/dL

(a) Due to increased testosterone

• Stimulates erythropoiesis

(b) Due to lack of cyclic bleeding

(2) Anemia in an adult male is an Hb < 13.5 g/dL

(3) Anemia in a nonpregnant woman is an Hb < 12.5 g/dL.

Anemia in nonpregnant female: <12.5 g/dL

e. Pregnancy

(1) Pregnant women have lower normal ranges than nonpregnant women.

(a) Due to an increase in plasma volume and RBC mass (i.e., more RBCs are produced)

Pregnancy: 2× greater increase in plasma volume than RBC mass

(b) Plasma volume is twice greater than RBC mass causing a slight decrease in Hb (dilutional effect).

(2) In a pregnant woman, anemia is a Hb < 11 g/dL.

2. Changes in thalassemia (i.e., a genetic globin chain disorder)

a. Hb and Hct are decreased.

b. RBC count is increased.

c. Mean corpuscular volume (MCV)/RBC count ratio < 13.

Thalassemia: ↓ Hb, Hct; ↑ RBC count; MCV/RBC < 13

3. Anemia

a. Decrease in Hb, Hct, or RBC concentration

b. O₂ saturation and PaO₂ are normal; decreased O₂ content (refer to Chapter 1).

Anemia: O₂ saturation and arterial PO₂ normal

c. Sign of an underlying disease rather than a specific diagnosis

Anemia: sign of disease; not a specific diagnosis

d. General clinical findings

(1) Fatigue

(2) Dyspnea with exertion

Anemia: ↓ O₂ content

(3) Inability to concentrate

(4) Dizziness

(5) Pulmonary flow murmur

• Decreased blood viscosity in severe anemia

(6) Pallor of skin, conjunctivae, palmar creases

• Indications of severe anemia

(7) High-output cardiac failure

• Decreased blood viscosity in severe anemia (<5 g/dL)

C. RBC indices

1. MCV

a. Average volume of RBCs

b. Used to classify anemia (Fig. 11-5)

11-5 Classification of anemia using mean corpuscular volume (MCV). An intrinsic RBC defect indicates a structural or biochemical flaw in the RBCs. An extrinsic RBC defect indicates that the RBCs are structurally normal, but that other factors cause the anemia. G6PD, glucose-6-phosphate dehydrogenase.

MCV: classification of anemias

(1) Microcytic (<80 μm³)

(2) Normocytic (80–100 μm³)

(3) Macrocytic (>100 μm³)

2. Mean corpuscular hemoglobin concentration (MCHC)

a. Average Hb concentration in RBCs (Fig. 11-6)

b. Decreased MCHC

(1) Correlates with decreased synthesis of Hb

• Example—all the microcytic anemias

(2) Central area of pallor is greater than normal.

• Called hypochromasia (see Fig. 11-11)

c. Increased MCHC

11-6 Normal peripheral blood smear showing RBCs. The RBCs are uniform in size, and the central areas of pallor are slightly less than half the total diameter of an RBC. The four dark objects (arrows) outside the RBCs are platelets.

(From Hoffbrand AV: Color Atlas: Clinical Hematology, 3rd ed. St. Louis, Mosby, 2000, p 22, Fig. 1-62.)

MCHC: ↓ in microcytic anemias; ↑ in spherocytosis

(1) Correlates with the presence of spherical RBCs

• Example—hereditary spherocytosis (see Fig. 11-25)

(2) RBCs lack the central area of pallor.

3. RDW

a. Reflects variation in size of peripheral blood RBCs

RDW: measure of size variation of RBCs

(1) Size variation is called anisocytosis.

(2) RDW is significant only if it is increased.

b. Increased if RBCs are not uniformly the same size

• Example—mixture of microcytic and normocytic cells

c. Iron deficiency

(1) Most common microcytic anemia with an increased RDW

(2) Due to a mixture of normocytic and microcytic RBCs

Iron deficiency: ↑ RDW

D. Characteristics of mature RBCs

1. Lack mitochondria; therefore:

a. No citric acid cycle

b. No β-oxidation of fatty acids

c. No ketone body synthesis

2. Anaerobic glycolysis

a. Main source of adenosine triphosphate (ATP).

Mature RBC: anaerobic glycolysis; lactic acid end-product

b. Lactic acid is the end-product of RBC metabolism.

(1) Converted by the liver into glucose via gluconeogenesis

(2) Glucose is utilized by RBCs for synthesizing ATP.

• This is called the Cori cycle.

Cori cycle: lactic acid converted to glucose in liver→ glucose to RBC

3. Pentose phosphate pathway

a. Synthesizes glutathione (GSH)

• Antioxidant that neutralizes hydrogen peroxide (refer to Chapter 2)

b. Hydrogen peroxide is a product of oxidative metabolism.

GSH: neutralizes peroxide and other free radicals

4. Methemoglobin reductase pathway (refer to Chapter 1)

a. Methemoglobin (metHb) refers to heme iron that is oxidized (Fe⁺³).

• MetHb cannot bind O₂.

b. Reductase system converts iron to ferrous (Fe⁺²) so that the RBCs can bind O₂.

MetHb reductase: reduces Fe⁺³ to Fe+²

5. Luebering-Rapaport pathway

a. Synthesizes 2,3-BPG

b. Required to right-shift the OBC (i.e., release O₂ to tissue; refer to Chapter 1)

2,3-BPG: product of the glycolytic cycle

6. Senescent RBCs

a. Phagocytosed in the cords of Billroth by splenic macrophages

b. Heme degradation by macrophages produces unconjugated bilirubin.

7. Lack human leukocyte antigens on their membranes (refer to Chapter 3)

Unconjugated bilirubin: end-product of heme degradation in macrophages

E. WBC count and differential

A 100 cell differential count divides leukocytes by percentage (neutrophils, lymphocytes, etc.) and further subdivides neutrophils into segmented and band neutrophils. Multiplication of the percentage times the total white blood cell count gives the absolute number of a particular leukocyte. Example—lymphocytes 30%, total WBC count 10,000/mm³. Absolute lymphocyte count is 0.30 × 10,000 = 3000/mm³.

F. Platelet count

1. Platelets are anucleate cells.

2. They are derived from cytoplasmic budding of megakaryocytes.

3. Platelets and their disorders are discussed in Chapter 14.

G. Iron studies (Fig. 11-7)

1. Serum ferritin

a. Ferritin is a soluble iron-binding storage protein.

11-7 Iron studies in normal people (A) and those with iron deficiency (B), anemia of chronic disease (C), and iron-overload diseases (D). See text for discussion.

Ferritin: synthesized in bone marrow macrophages

(1) Primary storage site is in bone marrow macrophages.

• See shaded area in the small box in Figure 11-7A.

(2) Serum levels directly correlate with ferritin stores in the macrophages.

(3) Synthesis of ferritin in macrophages increases in inflammation.

• Due to release of interleukin 1 and tumor necrosis factor-α

b. Decreased serum ferritin

• Diagnostic of iron deficiency (see Fig. 11-7B)

c. Increased serum ferritin

(1) Anemia of chronic disease (ACD) (Fig. 11-7C)

(2) Iron overload disease (Fig. 11-7D)

Serum ferritin: ↓ iron deficiency; ↑ ACD, iron overload disease

d. Hemosiderin

(1) Insoluble degradation product of ferritin

(2) Decreased and increased levels correlate with changes in ferritin stores.

2. Serum iron

a. Represents iron bound to transferrin

(1) Binding protein of iron

(2) Synthesized in the liver

b. Serum iron is the shaded area of the column in Figure 11-7A.

• Note that the normal serum iron level is ∼︀100 μg/dL.

c. Decreased serum iron

(1) Iron deficiency (see Fig. 11-7B)

(2) ACD (see Fig. 11-7C).

d. Increased serum iron

(1) Iron overload diseases (see Fig. 11-7D)

(2) Examples—sideroblastic anemia, hemochromatosis

Serum iron: ↓ iron deficiency, ACD; ↑ iron overload disease

3. Serum total iron-binding capacity (TIBC)

a. Serum TIBC correlates with the concentration of transferrin.

↓ TIBC = ↓ transferrin; ↑ TIBC = ↑ transferrin

(1) Height of the column in Figure 11-7A correlates with serum transferrin and TIBC.

(2) Note that the normal TIBC is ∼︀300 μg/dL.

b. Relationship of transferrin synthesis with ferritin stores in macrophages

(1) Decreased ferritin stores cause increased liver synthesis of transferrin (see Fig. 11-7B).

• Increase in transferrin and TIBC is present in iron deficiency.

(2) Increased ferritin stores causes decreased liver synthesis of transferrin (see Fig. 11-7C and D).

• Decrease in transferrin and TIBC occurs in ACD (see Fig. 11-7C) and iron overload disease (see Fig. 11-7D).

↓ Ferritin stores = ↑ TIBC; iron deficiency; ↑ ferritin stores = ↓ TIBC; ACD, iron overload

4. Iron saturation (%)

a. Percentage of binding sites on transferrin occupied by iron

(1) Iron saturation (%) = serum iron/TIBC × 100

(2) In Figure 11-7A, the normal % saturation is 100/300 × 100, or 33%.

b. Decreased iron saturation

(1) Iron deficiency (see Fig. 11-7B)

↓ Iron saturation: iron deficiency, ACD; ↑ iron saturation: iron overload disease

(2) ACD (see Fig. 11-7C)

c. Increased iron saturation

• Iron overload disease (see Fig. 11-7D)

H. Hb electrophoresis

1. Used to detect hemoglobinopathies (Fig. 11-8).

a. Abnormality in globin chain structure (e.g., sickle cell disease)

b. Abnormality in globin chain synthesis (e.g., thalassemia)

2. Types of normal Hb detected (Fig. 11-8A)

a. HbA has 2α/2β globin chains (97% in adults).

b. HbA₂ has 2α/2δ globin chains (2% in adults).

c. HbF has 2α/2γ globin chains (1% in adults).

11-8 Hemoglobin electrophoresis in various hemoglobinopathies. See text for discussion.

(From Goljan EF, Sloka KI: Rapid Review Laboratory Testing in Clinical Medicine. St. Louis, Mosby Elsevier, 2008, p 159, Fig. 5-12.)

HbA: 2α/2β HbA₂: 2α/2δ HbF: 2α/2γ

3. Examples of abnormal Hb detected

• Sickle Hb, HbH, Hb Bart

III. Microcytic Anemias

A. Types of microcytic anemias

1. Iron deficiency (most common)

2. Anemia of chronic disease (ACD)

3. Thalassemia (α and β)

4. Sideroblastic anemias (least common)

B. Pathogenesis (Fig. 11-9)

1. Defects in the synthesis of Hb

• Hb =heme + globin chains

11-9 Pathophysiology of microcytic anemias. See text for discussion. ALA, aminolevulinic acid.

Microcytic anemias: defects in the synthesis of Hb (heme + globin chains)

2. Defects in the synthesis of heme (i.e., iron + protoporphyrin)

• Iron deficiency, ACD, sideroblastic anemias

3. Defects in the synthesis of globin chains (i.e., α or β)

• α-Thalassemia, β-thalassemia (thal)

C. Iron deficiency anemia

1. Iron reabsorption

a. Approximately 10% of dietary iron (1–2 mg/day) is reabsorbed in the duodenum.

Types of iron: reduced Fe⁺² (heme iron in meat), oxidized Fe⁺³ (nonheme iron in plants)

(1) Iron from plants is in a nonheme, oxidized form (ferric, Fe⁺³).

• Oxidized form cannot be reabsorbed in the duodenum.

(2) Iron from meat is in a heme, reduced form (ferrous, Fe⁺²)

• Reduced form is directly reabsorbed in the duodenum.

Oxidized Fe⁺³ must be reduced to Fe⁺² for reabsorption in duodenum

b. Percentage of iron reabsorbed from the diet is increased in the following:

(1) Normal women who have cyclic bleeding

(2) Pregnancy and lactation

(3) Any anemia, regardless of type

• Danger of iron overload, if iron supplements are improperly prescribed

c. Most of the iron is attached to the four heme groups in Hb; the remainder is stored in the following:

(1) Marrow macrophages

Iron: majority stored in marrow macrophages

• Approximately 1000 mg in men and 400 mg in women

(2) Myoglobin

• Contains one heme group

(3) Enzymes, as a cofactor

d. Gastric acid frees elemental iron from heme and nonheme products.

• Underscores why achlorhydria (absent stomach acid) decreases availability of iron for reabsorption

e. Ascorbic acid is important in iron reabsorption.

Ascorbic acid: reduces nonheme iron to Fe+²

(1) Reduces Fe⁺³ in nonheme foods to the absorbable Fe⁺²

(2) Maintenance of iron homeostasis

f. Regulation of the amount of iron reabsorbed

(1) HFE (hemochromatosis) gene product facilitates binding of plasma transferrin with its mucosal cell transferrin receptor.

• This allows transferrin to be endocytosed (reabsorbed) by intestinal cells.

(2) Amount of endocytosed transferrin determines how much mucosal cell iron is released into the plasma to bind with transferrin.

2. Epidemiology of iron deficiency

a. It is the most common anemia.

Iron deficiency: most common overall anemia

b. Most common nutritional deficiency worldwide

c. Greatest prevalence

(1) Toddlers ages 1 to 2 years old

• Due to inadequate intake

(2) Females ages 12 to 49 years old

• Due to menstrual loss

d. Causes of iron deficiency (Table 11-1)

Table 11-1 Causes of Iron Deficiency Anemia

Iron deficiency: most commonly caused by bleeding

3. Pathogenesis

• Decreased synthesis of heme (see Fig. 11-9)

4. Clinical and laboratory findings

a. Plummer-Vinson syndrome

(1) Caused by chronic iron deficiency

(2) Esophageal web

• Dysphagia for solids but not liquids

Koilonychia: spoon nails; sign of iron deficiency

(3) Achlorhydria

• Absent acid in the stomach

(4) Glossitis

• Inflammation of the tongue

(5) Spoon nails (koilonychia; Fig. 11-10)

b. Some patients have a craving (pica) for ice.

c. Laboratory findings

(1) Decreased MCV

(2) Decreased serum iron, iron saturation

(3) Decreased serum ferritin (<30 ng/mL)

(4) Increased TIBC, RDW

11-10 Koilonychia. Note the spoon shape of the nail bed.

(From Savin JAA, Hunter JAA, Hepburn NC: Diagnosis in Color: Skin Signs in Clinical Medicine. London, Mosby-Wolfe, 1997, p 118, Fig. 4.60.)

Iron deficiency: ↓ iron, % saturation, ferritin; ↑ TIBC, RDW

The stages of iron deficiency in sequence are as follows: absent iron stores; decreased serum ferritin; decreased serum iron, increased TIBC, decreased iron saturation; normocytic normochromic anemia; microcytic hypochromic anemia.

Stages of iron deficiency: all lab studies abnormal before anemia is present

(5) Microcytic and normocytic cells with increased central area of pallor (Fig. 11-11)

(6) Increased serum free erythrocyte protoporphyrin (FEP)

• Less iron combines with protoporphyrin.

(7) Thrombocytosis

(a) Common finding in chronic iron deficiency

11-11 Peripheral blood smear in iron deficiency anemia. The enlarged central area of pallor in the red blood cell (arrows) indicates a decrease in hemoglobin synthesis, which is characteristic of the microcytic anemias. The mean corpuscular hemoglobin concentration is decreased.

(From Wickramasinghe SE, McCullough J: Blood and Bone Marrow Pathology. Philadelphia, Churchill Livingstone, 2003, Fig. 11-6.)

Thrombocytosis: common finding in chronic iron deficiency

(b) Reactive phenomenon to increase blood viscosity

(8) Leukocyte count is usually normal.

• Eosinophilia occurs in hookworm infestations.

5. Treatment

a. Ferrous sulfate, given orally

Rx iron deficiency: ferrous sulfate

b. Hct should increase ∼︀0.5% to 1%/day after the initial lag period.

c. Lack of response

(1) Noncompliance

(2) Continued blood loss

(3) Iron is not being reabsorbed.

D. Anemia of chronic disease (ACD)

1. Epidemiology

a. Most common anemia in hospitalized patients

ACD: most common anemia in hospitalized patients

b. Common causes

(1) Chronic inflammation

• Examples—rheumatoid arthritis, tuberculosis

ACD: most common anemia in malignancy, alcohol excess

(2) Alcoholism

• Most common overall anemia

(3) Malignancy

• Most common overall anemia

2. Pathogenesis

a. Decreased synthesis of heme (see Fig. 11-9)

b. Decrease renal production of EPO (some cases)

c. Liver synthesis and release of hepcidin

Hepcidin: antimicrobial peptide synthesized/released by liver

(1) Antimicrobial peptide released by the liver in response to inflammation

• Acute phase reactant (refer to Chapter 2)

(2) Enters macrophages in the bone marrow

• Prevents the release of iron to transferrin

Hepcidin: ↑ macrophage iron stores; “reticuloendothelial cell block”

(3) Ferritin synthesis and iron stores increase in bone marrow macrophages.

• Iron comes into the macrophage but only a little goes out.

3. Laboratory findings

a. Decreased MCV

b. Decreased serum iron, TIBC, iron saturation

ACD: ↓ iron, TIBC, % saturation; ↑ ferritin

c. Increased serum ferritin (>100 ng/mL)

d. Increased serum FEP

• Less iron combines with protoporphyrin.

e. Anemia rarely <9 g/dL.

4. Treatment

a. Treat the underlying disease causing the inflammation.

b. In some cases, giving EPO increases the Hb concentration.

E. Thalassemia (thal; α and β)

1. Epidemiology

a. Autosomal recessive disorders

Blacks: can have α- or β-thalassemia

b. α-Thal is common in Southeast Asians and in blacks.

c. β-Thal is common in blacks, Greeks, and Italians.

2. Pathogenesis of α-thal

a. Decrease in α-globin chain synthesis due to gene deletions (see Fig. 11-9)

α-Thal: due to gene deletions

• Four genes control α-globin chain synthesis.

b. One gene deletion produces a silent carrier.

• Not associated with anemia

c. The combination of two gene deletions is called α-thal trait (Fig. 11-12).

11-12 Gene deletions in α-thalassemia in the black population (A) and Asian population (B). Four α-genes are involved in α-globin chain synthesis. The black population type is associated with a loss of one gene on each chromosome (trans configuration: α/− α/−; schematic A). In the Asian type, there is a loss of both genes on the same chromosome (cis configuration: −/− α/α, B).

(From Goljan EF, Sloka KI: Rapid Review Laboratory Testing in Clinical Medicine. St. Louis, Mosby Elsevier, 2008, p 158, Fig. 5-11.)

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Jun 25, 2017 | Posted by admin in PATHOLOGY & LABORATORY MEDICINE | Comments Off

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