Mlab 1415 hematology keri brophy martinez
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MLAB 1415:Hematology Keri Brophy -Martinez. Chapter 10: The Hemoglobinopathies Part Two. Hemoglobin C Disease. Introduction. Amino acid substitution of lysine for glutamic acid at sixth position of Beta chain ( α 2 β 2 6Glu-Lys ) Is homozygous CC 

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MLAB 1415:Hematology Keri Brophy -Martinez

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MLAB 1415:HematologyKeri Brophy-Martinez

Chapter 10:

The Hemoglobinopathies

Part Two


Hemoglobin C Disease


Introduction

  • Amino acid substitution of lysine for glutamic acid at sixth position of Beta chain

    • (α2β26Glu-Lys)

  • Is homozygous CC 

  • Chronic hemolytic anemia with associated splenomegaly and abdominal discomfort


Laboratory Findings:Hb C Disease

  • Mild to moderate anemia (8-12 g/dL)

  • Retic count 4-8% (slightly increased)

  • Electrophoresis

    • Most hemoglobin is HbC

    • no HbA present

    • may or may not have increase in Hb F.


Peripheral Smear

  • Numerous target cells, few microspherocytes, schistocytes, and folded cells

  • May see hexagonal or rod-shaped crystals ("bar of gold”). 

    • Usually intracellular. Are elongated with blunt ends and parallel sides.


Hemoglobin C Trait (AC)

  • No symptoms – no anemia. 

  • Target cells frequent finding.


Treatment for Hb C

  • Splenectomy may be beneficial for symptomatic CC homozygous persons.

  • AC heterozygous persons are usually asymptomatic, so no treatment required.


Hemoglobin SC Disease

  • HbS gene is inherited from one parent and HbC gene is inherited from the other parent

    • so both β- chains are abnormal

  • Splenomegaly

  • Patients can develop vaso-occlusive crisis


Peripheral Smear

  • target cells

  • folded red cells

  • occasional glove-shaped intracellular crystals.


Hemoglobin E Disease


Hb E Disease

  • β chain variant – lysine substituted for glutamic acid in 26th position in beta chain

    • (α2β226Glu-Lys)

  • Heterozygous and homozygous forms.

  • Frequently occurs with Beta thalassemia

  • No clinical symptoms


Laboratory Findings:Hb E Disease

Similar to Hb D

Mild, microcytic, hypochromic hemolytic anemia

Many target cells

Electrophoresis shows E band. Normal Hb F, no Hb A

May protect against malaria


Unstable Hemoglobin Variants


Overview

Unstable hemoglobins are hemoglobin variants in which amino acid substitutions or deletions have weakened the binding forces that maintain the structure of the molecule.

Instability may cause Hb to denature and precipitate in the red cells as Heinz bodies.


Overview con’t

  • Most inherited as autosomal dominant disorders.

  • When anemia is present, degree of hemolysis varies considerably:

    • Most have mild compensated anemia with mild reticulocytosis

    • Some have severe, chronic hemolysis with splenomegaly and jaundice.

  • Hb electrophoresis usually not very helpful in diagnosis.


Hemoglobin Variants with Altered Oxygen Affinity


Methemoglobinemia (Hemoglobin M)


Overview

  • HbM contains ferric iron (Fe3+); Can’t carry oxygen and results in cyanosis.

  • Three causes of methemoglobinemia:

    • Methemoglobin reductase system

      • Overwhelmed

      • Deficient

      • Molecule is resistant to methemoglobin reductase


Hb M

5 variants of Hb M which result from single amino acid substitution in the globin chain that stabilizes iron in the ferric form.

Patients have cyanosis, but are otherwise asymptomatic and no treatment is given.


Laboratory Findings in Hb M

Blood is chocolate brown.

Mild hemolytic anemia.

Heinz bodies.

M band on electrophoresis.


Hemoglobinswith Increased Oxygen Affinity

Decreased delivery of oxygen to tissues.

Hb values from normal to 20 g/dL.

Leukocytes and platelets normal.

Normal life span.

No treatment.

Often results in polycythemia.


Hemoglobins with Decreased Oxygen Affinity

Increased release of oxygen to tissues.

Patient may become anemic.


Referenes

  • Harmening, D. M. (2009). Clinical Hematology and Fundamentals of hemostasis (5th ed.). Philadelphia, PA: F.A. Davis Company.

  • McKenzie, S. B. (2010). Clinical Laboratory Hematology (2nd ed.). Upper Saddle River, NJ: Pearson Education, Inc.

  • Rodak, B. F. (2002). Hematology Clinical Principles and Applications (3rd ed.). St. Louis: Saunders Elsevier.


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