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An Introduction to Hemoglobinopathies

An educational introduction to hemoglobin variants and thalassemias and the general laboratory approach to their investigation.

7 min read Hematology #rbc-indices #hematology #hemoglobinopathy #thalassemia
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Learning Objectives

By the end of this resource you should be able to:

- Distinguish structural hemoglobin variants from thalassemias at a general level.
- Identify common examples of structural hemoglobin variants.
- Describe the general laboratory approach to investigating a suspected hemoglobinopathy.
- Explain why iron studies are relevant when investigating microcytic anemia.

An Introduction to Hemoglobinopathies

Overview

Hemoglobinopathies are inherited disorders affecting the structure or production of hemoglobin. They are broadly divided into structural hemoglobin variants (such as hemoglobin S, C, and E) and thalassemias, which involve reduced production of one or more normal globin chains. This is a general educational overview; specific diagnosis and management require specialized clinical and laboratory expertise.

Normal hemoglobin background

Adult hemoglobin (HbA) is composed of two alpha and two beta globin chains. Smaller amounts of HbA2 (two alpha and two delta chains) and HbF (fetal hemoglobin, two alpha and two gamma chains) are normally present in adults in defined proportions. Hemoglobinopathies can affect the structure of these chains (variants) or their rate of production (thalassemias).

Structural hemoglobin variants

Structural variants result from a change in the amino acid sequence of a globin chain. Common examples include:

  • Hemoglobin S: associated with sickle cell disease and sickle cell trait, depending on whether one or two abnormal genes are inherited.
  • Hemoglobin C: associated with a generally milder condition, which can also interact with hemoglobin S when co-inherited.
  • Hemoglobin E: common in certain populations, can present with mild microcytosis and, when co-inherited with beta thalassemia, a more significant clinical picture.

Thalassemias

Thalassemias involve reduced or absent production of a normal globin chain:

  • Alpha thalassemia: results from deletion or, less commonly, mutation of one or more of the four alpha-globin genes, with clinical severity generally related to the number of affected genes.
  • Beta thalassemia: results from mutations affecting beta-globin gene expression, with clinical severity ranging from a mild trait to a more significant condition, depending on the specific mutations inherited.

General laboratory approach

Investigation of a suspected hemoglobinopathy commonly involves a combination of:

  • CBC and red-cell indices: thalassemias classically show microcytosis, often with a disproportionately low MCV relative to the degree of anemia, and can show a normal or elevated RBC count relative to the hemoglobin level.
  • Peripheral blood film examination: may show target cells, and other specific morphological features depending on the condition.
  • Hemoglobin electrophoresis or high-performance liquid chromatography (HPLC): separates hemoglobin fractions based on charge or other physicochemical properties, allowing quantification of HbA, HbA2, HbF, and detection of abnormal variants.
  • Solubility testing: a rapid screening test historically used to detect hemoglobin S, generally followed by a confirmatory method.
  • Molecular/genetic testing: used to characterize specific mutations, particularly relevant for alpha thalassemia (often not fully characterized by electrophoresis alone) and for definitive diagnosis or genetic counseling purposes.

Why iron studies matter in the differential

Because both iron deficiency and thalassemia trait can cause microcytic anemia, iron studies are commonly performed alongside hemoglobinopathy investigation to help distinguish between these possibilities, since the two conditions require different management approaches and can, in some cases, coexist.

Clinical relevance

Hemoglobinopathies are relevant to screening programs in some populations, genetic counseling, antenatal care, and the diagnosis and monitoring of affected individuals. Specific testing algorithms, interpretation, and counseling should follow recognized clinical and laboratory guidance and involve appropriately qualified professionals.

Key points

  • Hemoglobinopathies include structural variants (such as HbS, HbC, HbE) and thalassemias (reduced globin chain production).
  • Thalassemias classically cause microcytosis, sometimes disproportionate to the degree of anemia.
  • Hemoglobin electrophoresis or HPLC is a central technique for identifying and quantifying hemoglobin fractions.
  • Molecular testing is particularly important for characterizing alpha thalassemia.
  • Iron studies help distinguish thalassemia trait from iron deficiency, since both cause microcytic anemia.

References

  • NCBI. MeSH: Hemoglobinopathies; MeSH: Thalassemia.
  • World Health Organization. Laboratory Quality Management System: Handbook.
  • ISO 15189:2022. Medical laboratories — Requirements for quality and competence.