Hemoglobin: – Part 1 – Hemoglobin (Hb) structure and Functions
Sample for Hemoglobin (Hb)
- The blood sample is taken in EDTA.
- EDTA salt of sodium or potassium is the preferred sample.
- The blood sample is stable for 48 hours at 4°C and 24 hours at 23 °C.
Precautions for Hemoglobin (Hb)
- Avoid clotting (micro-clots may form), which will lower the Hb.
- Falsely high results may occur due to prolonged venous stasis during venipuncture.
- Increased turbidity, the presence of paraproteins, and nucleated RBCs give high values.
- Lipemic blood also gives high values.
- There is a false low Hb in pregnancy due to increased blood volume.
- In the high altitude area, the Hb will be high.
- Gentamicin and methyldopa may increase Hb value.
- Antibiotics, chemotherapy, aspirin, and sulphonamide gives low values.
Purpose of the test (Indications) for Hemoglobin (Hb):
- It is done to diagnose anemia.
- It tells the severity of anemia.
- It will monitor the effectiveness of the treatment of anemia.
- This is done to evaluate polycythemia.
- This is a part of the complete blood examination.
Definition of the Hemoglobin (Hb):
- Hemoglobin is an oxygen-carrying compound present in the RBCs.
- Total hemoglobin depends upon the number of RBCs in the blood.
- RBCs are the hemoglobin carriers.
- Hemoglobin is a hemoprotein whose primary function is to transport oxygen from the lungs to the body tissues.
- It was first isolated in 1849.
Pathophysiology for Hemoglobin (Hb):
- Hb is a globular protein with a diameter of 6.4 nm in diameter.
- Hb A has a molecular weight of 68,000, and one RBC contains 640 million Hb molecules.
- Hb consists of four polypeptide chains, 2α and 2β, and heme groups. The 4 iron atoms are in the ferrous state (Fe++).
- Heme synthesis takes place in the mitochondria.
- The blood sample contains 96% of the Hb.
|Age or stage of the fetus||Hb type||Structure|
|In early embryonic life||
|At the 6th week of gestation||
|At 28, the week of gestation||
- Zeta (ζ) chain production ceases at the gestational age of around 4 months.
- 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.
- 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.
- 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.
- The environment and chemicals modify a hemoglobin molecule, and the types are:
Globin gene location on the chromosomes:
- 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.
- The β, γ, and δ globins genes are clustered closely on chromosome 11.
Synthesis of hemoglobin:
- The biosynthesis of hemoglobin requires the synthesis of heme and globin polypeptide chains.
- Hb consists of protein portions as Globin and iron part as heme.
- Hemoglobin synthesis is a complicated process. This takes place in the red blood cells.
- Amino acids are assembled in the ribosomes and give rise to α2 β2 globulin.
- Transferrin gives Iron which will combine with the haem molecule.
- Heme molecule will have protoporphyrin by the chemical combination of glycine and succinyl CoA in the presence of Vitamin B6 and form heme.
- Heme molecule consists of protoporphyrin IX protein and iron (Fe++).
- Protoporphyrin IX + Fe++ = Heme.
- Hb is the iron-containing pigment of the RBCs, carrying oxygen to various body parts.
- A central part of the Heme (iron-porphyrin) group is the site of Oxygen uptake and release.
- Hb, serve as the main vehicle for the transportation of oxygen and carbon dioxide.
- It carries oxygen from the lung to tissues.
- CO2 from the tissue to the lung.
- It carries oxygen from the lung to tissues.
- Iron combines with oxygen and gives it a red color.
- The oxygen combining capacity is directly related to Hb concentration, not the number of RBCs.
- The iron of heme is in Fe++ form, and it can combine irreversibly with oxygen and has a major role as an oxygen carrier.
- Hb acts as a buffer in the extracellular fluid (acid-base buffer system).
- In tissues, the oxygen concentration is lower, and CO2 and H+ ions concentration is higher.
- When the pH is lower, then oxygen dissociates from Hb.
- Now deoxygenated Hb will bind to H ions and then raise the pH.
- CO2 diffuses into RBCs and forms carbonic anhydrase, converting CO2 to HCO3¯ and protons.
- Protons are bound to Hb HCO3¯ ions and leave the cell.
- Every HCO3¯ ion leaving the cell will lead to the entry of a chloride ion.
- This buffer system depends on the lungs and kidneys to eliminate CO2 and HCO3¯.
- Abnormalities in the globin structure lead to hemoglobinopathies like Sickle cell anemia and Hb C disease.
- In thalassemia, the globin chain synthesis is abnormal.
- Hb closely reflects the hematocrit and RBC count.
- Hb at birth is usually lower in premature infants.
- There is no significant change in Hb concentration after 85 years.
- The main function of hemoglobin is transporting oxygen to the tissues and removing carbon dioxide.
Signs and symptoms due to Hb level:
- There are >800 variants of hemoglobin. Only 9 variants and thalassemia have significance.
- Low Hb:
- It puts a strain on the cardiopulmonary system to maintain the oxygen level.
- There is a risk of angina, heart attack, and congestive heart failure.
- High Hb:
- The chances for intravascular settling.
- Infarction in other organs.
Normal values of Hemoglobin
|18 to 20 weeks||11.7 ± 0.78|
|21 to 22 weeks||12.28 ± 0.89|
|23 to 25 weeks||12.40 ± 0.77|
|26 to 30 weeks||13.35 ± 1.17|
|Cord blood||13.5 to 20.5|
|0.5 month||13.4 to 19.8|
|1 month||10.7 to 17.1|
|2 month||9.4 to 13.0|
|4 month||10.3 to 14.1|
|6 month||11.1 to 14.1|
|9 month||11.4 to 14.0|
|one year||11.3 to 14.1|
|0.5 to 2 years||11.0 to 14.0|
|2 to 5 years||11.0 to 14.0|
|5 to 9 years||11.5 to 14.5|
|9 to 12 years||12.0 to 15.0|
|12 to 14 years||12.0 to 16.0||11.5 to 15.0|
|15 to 17 years||11.7 to 16.6||11.7 to 15.3|
|18 to 44 years||13.2 to 17.2||11.7 to15.5|
|45 to 64 years||13.1 to 17.2||11.7 to 16.0|
|65 to 74 years||12.6 to 17.4||11.7 to 16.1|
- To convert into SI units x 10 = g/L
- Women = 12 to 16 g/dl
- Men = 14 to 17.4 g/dl
- Pregnant women = > 11 g/dl.
Normal values in Infants and Children
|0 to 2 weeks||14 to 24.5 g/dl|
|2 to 8 weeks||12.5 to 20.5 g/dl|
|2 to 6 months||10.7 to 17.3 g/dl|
|1 to 6 years||9.5 to 14.1 g/dl|
|6 to 16 years||10.3 to 14.9 g/dl|
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):
- Blood transfusion is not recommended as long as the Hb is above 8 g/dl. and Hct is above 24 %.
- Hb < 5 g/dl is critical and needs a blood transfusion.
- In older patients, blood transfusion is recommended when the Hb level is below 10 g/dl.
- Hemoglobin <7 g/dL.
- >20 g/dL.
Increased Hemoglobin (Hb) is seen in:
- Polycythemia vera.
- Congestive heart failure.
- Chronic obstructive pulmonary disease (COPD).
- After vigorous exercise.
- Hemoconcentration, like dehydration, burns, and severe vomiting.
- Intestinal obstruction.
- Severe dehydration like diarrhea and burns.
Decreased Hemoglobin (Hb) is seen in:
- Drugs that cause aplastic anemia.
- Drugs that cause hemolysis ( G6PD deficiency ).
- Immune hemolytic anemia.
- Iron deficiency anemia.
- Pernicious anemia.
- Liver diseases and Cirrhosis.
- The hemorrhage is acute or chronic, like bleeding hemorrhoids or ulcers.
- Hodgkin’s disease.
- Multiple myelomas.
- Autoimmune diseases.
- Rheumatoid arthritis.
- Dietary deficiency.
- Deficiency of iron.
- Deficiency of vitamin B12 and folic acid.
- Malabsorption syndrome.
Questions and answers:
Question 1: What is the main function of the hemoglobin?
Main function of the hemoglobin is to carry oxygen to tissues and bring CO2 to lungs.
Question 2: What is the role of hemoglobin in the extracellular space?
In the extracellular space, hemoglobin acts a s a buffer.