Hemoglobin (Hb) is a protein found in erythrocytes in the blood. Hemoglobin is a tetrameric molecule consisting of "heme" groups and four linked "globin" chains.

Hemoglobin (Hb) is a protein found in erythrocytes in the blood. Hemoglobin is a tetrameric molecule consisting of “heme” groups and four linked “globin” chains.

Functions of hemoglobin in the blood:

  • Transport of oxygen from the lungs to the tissues
  • Transport of carbon dioxide and protons from the tissues to the lungs
  • Keeping the pH of blood and indirectly other body fluids constant

Hemoglobins do their job by being inside erythrocytes. The average lifespan of the hemoglobin molecule is 120 days. At the end of this period, the destruction of hemoglobin begins with the breakdown of erythrocytes in the liver, bone marrow and spleen. In the molecule of Hemoglobin, which is released after destruction, first the “heme” and “globin” parts are separated from each other. The “heme” group is also divided into the iron and porphyrin parts. While the released iron is stored for reuse, porphyrin is oxidized to “biliverdin” and biliverdin to “bilirubin”. Polypeptide chains are broken down into amino acids and these amino acids are stored. In other words, iron and bilirubin are released as a result of hemoglobin breakdown.



Normally, about 2.3 cm3 of oxygen can be dissolved in 100cm3 of human blood. However, the need for oxygen in daily life is much more than that. For this reason, the needed blood is stored by binding with hemoglobins and used when needed. Hemoglobin molecules, which are on average 15 g in 100 ml of blood, can bind and store up to 65 times the amount of oxygen that can be dissolved in the same amount of blood. In this way, 97% of the oxygen amount in the blood is transported depending on Hemoglobins, and the body’s oxygen need is compensated.

Normal hemoglobin concentration in blood is approximately:

  • 14-18% for adult male
  • 12-15% gr for adult woman
  • 12-13% for child
  • 21% g for newborn

Hemoglobins are classified in many different ways. For example, according to their affinity for oxygen, hemoglobins are:

  • tense -tense) hemoglobins with low affinity for oxygen
  • R ( relaxed ) hemoglobins with high affinity for oxygen

There are factors that affect the affinity of hemoglobin for oxygen. Some of those:

  • 2,3-diphosphoglycerate (DPG) in the environment reduces the affinity of hemoglobin for oxygen.
  • When the ambient temperature increases, the affinity of hemoglobin for oxygen increases to some extent.
  • Changes in the amino acid sequences of hemoglobin can change the type of hemoglobin, reducing or increasing its affinity for oxygen.

All normal hemoglobins function in a quaternary structure with contributions from two alpha (α) and two beta (β) globin chains. The amino acid contents in the alpha and beta globin chains cause the formation of hemoglobins of different types and abilities.



Hemoglobin structure has structural differences in the same person in the womb (embryonic and fetal period) and adulthood. These differences are due to the different types of protein chain in the hemoglobin structure. These chains differ according to the needs at different stages of the life cycle. For example:

  • In the embryonic period; Alpha globin-like chains (ζ, zeta chains) coordinated with the alpha gene family on chromosome 16 and gamma (Hb Portland, ζ2γ2) or epsilon globin chains (Hb Gower 1, ζ2ε2), (Hb Gower 2, α2ε2) form the quaternary structure is occurring.
  • During fetal and adulthood: In addition to the alpha globin chain, which is coordinated with the beta gene family in the 11th chromosome, beta (Hb A, α2β2), delta (Hb A2, α2δ2) or gamma globin chain (Hb F, α2γ2) occurs.
  • HbF occurring in the fetal period decreases over time and leaves its place to HbA and HgbA2 hemoglobins.

Due to gene mutations in alpha and beta globin chains in hemoglobin, differences in amino acid sequences may occur. The alpha chain consists of 141 amino acids and the beta chain consists of 146 amino acids, and the combinations of changes in these sequences cause the formation of different hemoglobins. Because of these changes, hundreds of different types of abnormal hemoglobin have been identified.

Hgb levels are measured to assess the hemoglobin content in the blood. This can also be done to help screen for and diagnose conditions affecting erythrocytes. If there is low or high hemoglobin, it is evaluated and medical intervention plans are made. If there is a hemoglobin test, it is used together with other tests (hematocrit, RBC, MCV levels, etc.) to check for anemia. Decreased hemoglobin levels may indicate anemia. It can also decrease in case of any bleeding or in cases of hemolysis in which the cells are broken down in the vessel. High hemoglobin levels can also be detected in diseases such as polycythemia vera, in which cell numbers increase abnormally. In such cases, additional tests and examinations may be required to determine the cause.

The most common causes of decrease in Hgb levels are:

  • Deficiencies in erythrocyte production
    • Inadequacy of essential nutrients
      • Vitamin B12
      • Folic acid
      • Iron
    • Bone marrow damage
      • Radiation
    • suppression of the bone marrow
      • Medicines
      • Immunological agents
      • Radiation
    • Invasion of the bone marrow
      • Cancers
      • Fibrosis
    • Hereditary defects
    • Endocrine problems
      • Hypothyroidism
      • Hypopituitarism
      • Kidney failure
    • Idiopathic causes
  • Defects in erythrocytes
    • Abnormal hemoglobins
      • Hemoglobin S
      • Hemoglobin C
      • Hemoglobin D
      • Hemoglobin E
      • Hemoglobin Gun Hill
      • Hemoglobin H
      • Hemoglobin Bart
      • Hemoglobin M
    • Defects in globin synthesis
      • Thalassemia
    • Defects in heme synthesis
      • Porphyria
    • Attachment of another molecule instead of oxygen
      • Carbaminohemoglobin (CO2 binding)
      • Carboxyhemoglobin (Hb⋅CO)
      • Methemoglobin (Inability of O2 or CO to bind as a result of oxidation of Fe+2 in hemoglobin to Fe+3)
      • Sulfhemoglobin (H2S binding)
      • Nitrogen monoxide hemoglobin (breathing nitric fumes)
      • Cyanhemoglobin (HCN inhalation)
      • Cyanmethemoglobin (removal of inorganic cyanide)
    • Carbohydrate enzyme defect
      • G-6-PD deficiency
      • Pyruvar Kinase deficiency
    • Membrane defect
      • Hereditary spherocytosis
      • Elliptocytosis
    • Paroxysmal nocturnal hemoglobinuria
  • Causes other than erythrocytes
    • Secondary causes
      • Physical agents
      • This
      • Thermal damage
      • Microangiopathy
    • Chemical agents
      • Poisons and toxins
      • Medicines
    • Infections
      • Malaria
      • Septicemia
    • Neoplasms
      • lymphoma
      • Other neoplasms
    • Connective tissue diseases
      • Systemic Lupus Erythematosus
      • Other connective tissue diseases
    • Splenomegaly
    • Acute blood loss
    • Uremia
    • Chronic diseases
    • Alcoholism
    • Liver diseases
    • Conditions that cause hemolysis
    • Isoimmunization
      • Newborn
      • blood transfusion
    • Paroxysmal cold hemoglobinuria
  • Primary causes
    • Idiopathic causes (usually autoimmune causes)



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