Hemoglobin: – Part 1 – Hemoglobin (Hb) structure and Functions

Hemoglobin (Hb)

Sample for Hemoglobin (Hb)

1. The blood sample is taken in EDTA.
   1. EDTA salt of sodium or potassium is the preferred sample.
2. The blood sample is stable for 48 hours at 4°C and 24 hours at 23 °C.

Precautions for Hemoglobin (Hb)

1. Avoid clotting (micro-clots may form), which will lower the Hb.
2. Falsely high results may occur due to prolonged venous stasis during venipuncture.
3. Increased turbidity, the presence of paraproteins, and nucleated RBCs give high values.
4. Lipemic blood also gives high values.
5. There is a false low Hb in pregnancy due to increased blood volume.
6. In the high altitude area, the Hb will be high.
7. Gentamicin and methyldopa may increase Hb value.
8. Antibiotics, chemotherapy, aspirin, and sulphonamide gives low values.

Purpose of the test (Indications) for Hemoglobin (Hb):

1. It is done to diagnose anemia.
2. It tells the severity of anemia.
3. It will monitor the effectiveness of the treatment of anemia.
4. This is done to evaluate polycythemia.
5. This is a part of the complete blood examination.

Definition of the Hemoglobin (Hb):

1. Hemoglobin is an oxygen-carrying compound present in the RBCs.
2. Total hemoglobin depends upon the number of RBCs in the blood.
3. RBCs are the hemoglobin carriers.
4. Hemoglobin is a hemoprotein whose primary function is to transport oxygen from the lungs to the body tissues.
5. It was first isolated in 1849.

Pathophysiology for Hemoglobin (Hb):

1. Hb is a globular protein with a diameter of 6.4 nm in diameter.
2. Hb A has a molecular weight of 68,000, and one RBC contains 640 million Hb molecules.
   1. Hb consists of four polypeptide chains, 2α and 2β, and heme groups. The 4 iron atoms are in the ferrous state (Fe++).
   2. Heme synthesis takes place in the mitochondria.
   3. The blood sample contains 96% of the Hb.

Age or stage of the fetus	Hb type	Structure
In early embryonic life	Gower 1 Gower 2 Portland 1 Portland 2	ζ2 ε2  (zeta + epsilon) α2 ε2  (alpha + epsilon) ζ2γ2 (zeta + gamma) ζ2β2 (zeta + beta)
At the 6th week of gestation	Fetal Hb HbF in adults (<1.0%)	α2 γ2  (alpha + gamma)
At 28, the week of gestation	Hb A1 Hb A2 (2.5% to 3.0%)	α2 β2  (alpha and beta) α2δ2  (alpha + delta)

3. Zeta (ζ) chain production ceases at the gestational age of around 4 months.
4. Production of α-chain and β-chain starts at about the 6th week of gestation. Hb F  (α2 γ2) increases in concentration, becoming the main hemoglobin in the fetus.
5. Hb A (α2β2) starts at the gestational age of 28the weeks and, at birth, can form up to 15% of the total hemoglobin. Rest mainly HbF and a very small amount of Hb A2.
6. Production of the γ-chain decreases after birth, and normal adult Hb F values are obtained by one year of infants. In some cases, it may be raised for 2 years.
7. The environment and chemicals modify a hemoglobin molecule, and the types are:
   3. Carboxyhemoglobin.
   4. Methemoglobin.
   5. Sulfhemoglobin.

Globin gene location on the chromosomes:

1. The gene that controls α-like and ζ-globin chains are located in a cluster of chromosome 16 at position 16p 13.3 near the chromosome 16 telomere.
2. The β, γ, and δ globins genes are clustered closely on chromosome 11.

Globin Genes location

Globin gene location

Synthesis of hemoglobin:

1. The biosynthesis of hemoglobin requires the synthesis of heme and globin polypeptide chains.
2. Hb consists of protein portions as Globin and iron part as heme.
3. Hemoglobin synthesis is a complicated process. This takes place in the red blood cells.
   1. Amino acids are assembled in the ribosomes and give rise to α2 β2 globulin.
   2. Transferrin gives Iron which will combine with the haem molecule.
   3. Heme molecule will have protoporphyrin by the chemical combination of glycine and succinyl CoA in the presence of Vitamin B6 and form heme.
      1. Heme molecule consists of protoporphyrin IX protein and iron (Fe⁺⁺).
      2. Protoporphyrin IX + Fe⁺⁺ = Heme.

Hemoglobin synthesis in RBC

4. Hb is the iron-containing pigment of the RBCs, carrying oxygen to various body parts.
   1. A central part of the Heme (iron-porphyrin)  group is the site of Oxygen uptake and release.

RBC function to carry O2

Hemoglobin normal structure

Hemoglobin types

Hemoglobin functions:

1. Hb, serve as the main vehicle for the transportation of oxygen and carbon dioxide.
   1. It carries oxygen from the lung to tissues.
      1. CO2 from the tissue to the lung.

The main role of hemoglobin is to supply O2 to the tissues

Hemoglobin’s role in Oxygen and CO2

2. Iron combines with oxygen and gives it a red color.
   1. The oxygen combining capacity is directly related to Hb concentration, not the number of RBCs.
   2. The iron of heme is in Fe⁺⁺ form, and it can combine irreversibly with oxygen and has a major role as an oxygen carrier.

Hemoglobin’s role in carrying oxygen to various tissues

3. Hb acts as a buffer in the extracellular fluid (acid-base buffer system).
   1. In tissues, the oxygen concentration is lower, and CO2 and H⁺ ions concentration is higher.
   2. When the pH is lower, then oxygen dissociates from Hb.
   3. Now deoxygenated Hb will bind to H ions and then raise the pH.
   4. CO2 diffuses into  RBCs and forms carbonic anhydrase, converting CO2 to  HCO3¯ and protons.
   5. Protons are bound to Hb  HCO3¯ ions and leave the cell.
   6. Every HCO3¯ ion leaving the cell will lead to the entry of a chloride ion.
   7. This buffer system depends on the lungs and kidneys to eliminate CO2 and HCO3¯.
4. Abnormalities in the globin structure lead to hemoglobinopathies like Sickle cell anemia and Hb C disease.
   1. In thalassemia, the globin chain synthesis is abnormal.
5. Hb closely reflects the hematocrit and RBC count.
6. Hb at birth is usually lower in premature infants.
7. There is no significant change in Hb concentration after 85 years.
8. The main function of hemoglobin is transporting oxygen to the tissues and removing carbon dioxide.

Signs and symptoms due to Hb level:

1. There are >800 variants of hemoglobin. Only 9 variants and thalassemia have significance.
2. Low Hb:
   1. It puts a strain on the cardiopulmonary system to maintain the oxygen level.
   2. There is a risk of angina, heart attack, and congestive heart failure.
   3. Stroke.
3. High Hb:
   1. The chances for intravascular settling.
   2. Stroke.
   3. Infarction in other organs.

Normal values of Hemoglobin

Source 1

• To convert into SI units x 10 = g/L

Another source

1. Women = 12 to 16 g/dl
2. Men = 14 to 17.4 g/dl
   1. Pregnant women = > 11 g/dl.

Another source

Normal values in Infants and Children

Normal value in Cord blood

• 9 month = 11.4 to 14 g/dl
• The normal values should be decided according to the population of various countries.

Normal values of a different fraction of Hb in the adult:

• Hemoglobin A 2  =  1.5 to 3.5 % of the total Hb.
• Hemoglobin F  = < 1% of total Hb.
• Hemoglobin in plasma  = 0.5 to 5.0 mg/dL.
• Methemoglobin  = < 1% of total Hb.

Critical values of Hemoglobin (Hb):

1. Blood transfusion is not recommended as long as the Hb is above 8 g/dl. and Hct is above 24 %.
2. Hb < 5 g/dl is critical and needs a blood transfusion.
3. In older patients, blood transfusion is recommended when the Hb level is below 10 g/dl.
4. Hemoglobin <7 g/dL.
   1. >20 g/dL.

Increased Hemoglobin (Hb) is seen in:

1. Polycythemia.
   1. Polycythemia vera.
   2. Congestive heart failure.
   3. Chronic obstructive pulmonary disease (COPD).
2. After vigorous exercise.
3. Hemoconcentration, like dehydration, burns, and severe vomiting.
4. Intestinal obstruction.
5. Severe dehydration like diarrhea and burns.

Decreased Hemoglobin (Hb) is seen in:

1. Anemia.
2. Drugs that cause aplastic anemia.
3. Drugs that cause hemolysis ( G6PD deficiency ).
4. Immune hemolytic anemia.
5. Iron deficiency anemia.
6. Thalassemia.
7. Pernicious anemia.
8. Hemoglobinopathies.
9. Liver diseases and Cirrhosis.
10. Hypothyroidism.
11. The hemorrhage is acute or chronic, like bleeding hemorrhoids or ulcers.
12. Malignancies:
    1. Hodgkin’s disease.
    2. Leukemia.
    3. Lymphomas.
    4. Carcinomatosis.
    5. Multiple myelomas.
13. Autoimmune diseases.
    1. SLE.
    2. Sarcoidosis.
    3. Rheumatoid arthritis.
14. Dietary deficiency.
    1. Deficiency of iron.
    2. Deficiency of vitamin B12 and folic acid.
    3. Malabsorption syndrome.

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