There are 3 varieties of normal haemoglobins:
1. Haemoglobin A — Here the molecule of Hb contains two different pairs of polypeptide chains. The ones in each chain are similar to each other but varies with the chains of the other pair. The pairs of chains are known as α and β chains.
2. Haemoglobin A2— The Hb contains 2α polypeptide chains and two other polypeptide chains which are different from β chains and are termed as δ chains. Its normal presence is in 2% of the total haemoglobin.
3. Haemoglobin F — Hb F or foetal haemoglobin is present in newborn foetus upto the extent of 80% (maximum), the rest being adult Hb. As the infant grows in age the percentage of Hb F decreases and that of the adult variety increases. By two years of age, blood will not have any Hb F. In foetal Hb, two of the polypeptide chains are of α variety and two are different and are termed as ϒ type.
1. In haemoglobin H (β4) and haemoglobin Barts (ϒ4), the normal polypeptide chains are abnormally conjugated.
2. In haemoglobin S, haemoglobin C, haemoglobin E and haemoglobin Dpunjab there are substitution of some amino acids at some points by some others which are not there in normal haemoglobin.
The abnormal haemoglobins are variants of adult haemoglobin. Hence they become conspicuous only after about 6 months of birth. ABNORMAL HAEMOGLOBINS CAN BE DETECTED BY PAPER ELECTROPHORESIS. The foetal Hb can be differentiated by its property of : 1. Alkali resistance and by 2. Ultra-violet absorption curve. Sickled cells can be demonstrated under the microscope by reducing the Hb by addition of 2% solution of sodium metabisulphite and incubating the mixture on a glass slide, in a moist chamber, at 37°C for 1/2 hour. Crescent or sickle shaped R.B.C.s will be seen, when the slide is examined under a microscope after this time.
Medico-legal aspects of abnormal haemoglobins —
1. Haemoglobin A1 and A2 are normal varieties, in adults and children above 2 years of age.
2. Haemoglobin F is normal in new-borns and in decreasing rates, up to the age of 2 years, by which time it is totally removed. This point may be helpful also to determine the age of infants and young children.
3. Abnormal haemoglobins have importance as being natural cause of death.
4. Inheritance of abnormal haemoglobins have importance in deciding of paternity and maternity disputes.
5. Abnormal haemoglobins have also importance for identification of a person in other circumstances.