Hemoglobin variants are abnormal forms of hemoglobin. Normal hemoglobin types in human blood include:

-           HbA makes up about 95% - 98% of Hb found in adults

-           HbA2 makes up about 2% - 3% of Hb found in adults

-           HbF makes up about 2% of Hb found in adults

Hemoglobin variants occur when genetic changes in the globin genes cause alterations in the amino acids that make up the globin protein. These changes may affect the structure of the hemoglobin. There are four genes that code for alpha globin chains and two genes that code for the beta globin chains. The most common alpha-chain-related condition is alpha thalassemia and most common beta-chain-related condition is beta thalassemia.

In thalassemia diseases, mutations of one or more globin genes cause reduction of globin chain production. As a result of this situation the percentage of minor hemoglobins (HbA2 and HbF) increases.

Hemoglobin E is one of the most common beta chain hemoglobin variants. People who are homozygous for HbE generally have a mild hemolytic anemia and a mild enlargement of the spleen.

HbC disease is rare and relatively mild. It usually causes a minor amount of hemolytic anemia and a mild to moderate enlargement of the spleen.

HbS is the primary hemoglobin in people with sickle cell disease.