Types of hemoglobin

What is hemoglobin?

The hemoglobin (Hb) is a globular protein containing iron majority in red blood cells . It is of enormous importance for the normal functioning of the human body, since it is responsible for the transport of oxygen through the blood from the lungs to all tissues. It also carries the carbon dioxide that is generated in the energy production process, to be removed later by exhalation.

Hemoglobin classification

Five classes of normal hemoglobin are recognized, which are those of healthy individuals, and numerous abnormal variants associated with the presence of genetic alterations. Such congenital defects lead to the synthesis of hemoglobins with defects in the structure of their polypeptide chains or in their three-dimensional conformation, which result in functional failures.

Normal hemoglobins are as follows:


  • Gower 1 (ξ 2 ε 2 )
  • Gower 2 (α 2 ε 2 )
  • Portland hemoglobin (ξ 2 γ 2 )


  • Hemoglobin F (α 2 γ 2 )


  • Hemoglobin A (α 2 β 2 ) – is the one found in the highest proportion
  • Hemoglobin A2 (α 2 δ 2 ) – in low percentage in healthy individuals (2.5%)
  • Hemoglobin F (α 2 γ 2 ) – limited to a fraction of erythrocytes (F cells).

Among the abnormal variants we can mention hemoglobins C, D, E, G, H, I, J, K, L, M, N, and S. S and C are the most prevalent abnormal variants and those responsible of the highest number of congenital hemoglobinopathies. Hematology studies these defects in detail.

Oxidation states

In its normal functioning, hemoglobin is in two possible oxidation states, in a harmonic balance:

-Hemoglobin (reduced state) – venous blood

-Oxyhemoglobin (oxidized state) – bound to oxygen, typical of arterial blood. This fraction can increase excessively due to heart disease, height effect, etc.

-Carbaminohemoglobin: formed when hemoglobin binds CO 2 after gas exchange between red blood cells and tissues. It is a normal form of transport and disposal of carbon dioxide.

Other classes of hemoglobins

Other forms of hemoglobin appear in particular conditions. They are types that must be in minimal proportions or they must not exist directly, and in disease conditions they appear (hemoglobinopathies). The main types are mentioned below:

-Metahemoglobin : is one in which the heme group has iron in a ferric state or Fe (III) , that is, oxidized, instead of being as Fe (II). This type of hemoglobin has too high an affinity for oxygen, which reduces its ability to release it to the tissues, which thus suffer from hypoxia. The presence of methemoglobin in proportions that exceed normal values ​​(1%) may be due to congenital defects or exposure to certain substances (toxic, certain drugs, etc.).

-Sulfohemoglobin : it is formed by the reaction of hemoglobin with inorganic sulfides and peroxide . It is generally due to the consumption of certain sulfur drugs (for example, sulfonamides). This irreversible change alters the oxygen transport capacity.

-Carboxyhemoglobin: arises from the binding of carbon monoxide to the hemoglobin molecule. It is one of the most serious forms of poisoning (for example, gas leaks in homes)

-Glycated hemoglobin : it is normally found in low quantity, but in diseases such as diabetes this type of hemoglobin increases drastically.

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