What is the difference between HbA, HbS, HBA and HBB?

HbA, HbS, HBA and HBB are the terms that confuse us when we learn about genetic diseases like sickle cell anemia and thalassemia. Let's understand the difference between them through this article.

There are several variants of hemoglobin that can exist in humans. For example:

  • Hemoglobin F (HbF): This is fetal hemoglobin, which is the dominant type of hemoglobin during fetal development. It is gradually replaced by HbA after birth.
  • Hemoglobin A (HbA): This is Adult hemoglobin. "A" stands for "adult" or "normal."
  • Hemoglobin A2 (HbA2): This is a minor form of adult hemoglobin, typically making up a small percentage of the total hemoglobin in adults.
  • Hemoglobin S (HbS): This is the abnormal hemoglobin associated with sickle cell anemia.


In the context of thalassemia, HBA and HBB are used to denote different types of hemoglobin chains:

HBA (Alpha Globin): 

HBA refers to the alpha globin chains. Alpha globin is one of the two types of protein chains that make up adult hemoglobin, with the other type being beta globin. Normal adults typically have two copies of the alpha globin gene (HBA) on each chromosome 16, for a total of four alpha globin genes.

HBB (Beta Globin): 

HBB refers to the beta globin chains. Beta globin is the other type of protein chain that makes up adult hemoglobin. Normal adults typically have two copies of the beta globin gene (HBB) on each chromosome 11, for a total of four beta globin genes.

In thalassemia, there can be mutations or deletions in either the alpha globin (HBA) or beta globin (HBB) genes, which lead to abnormalities in hemoglobin production. The specific type and severity of thalassemia depend on which globin chain is affected and to what extent.

So, HbA is the complete hemoglobin molecule that consists of both alpha and beta globin chains, while HBA and HBB refer to the individual globin chains that make up hemoglobin.

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