Easy Pediatrics

Hemoglobin is a iron containing protein in the red blood cells that carries oxygen in the blood from the lungs to the rest of the body tissues. A normal hemoglobin level is necessary for the normal function of  the body. If there is decreased or abnormal hemoglobin synthesis it results in number of different diseases.

Here we will discuss the brief physiology of hemoglobin in the human body which helps in understanding the diseases related to abnormal hemoglobin.

Hemoglobin Synthesis

• Erythropoietic activity is regulated by erythropoietin.
• The mitochondria of the developing erythroblast are the main sites for the sythesis of haem.
• The globin protein part is synthesized in the ribosomes .
• There are number of complex series of steps for the synthesis of hemoglobin.
• The Vitamin B6 acts as a cofactor in the process of synthesis.
• The Fe is supplied by the circulating transferrin.
• A tetramer of four globin chains, each with its own haem group attached, is formed to make a molecule of hemoglobin.

Structure and Different Types of hemoglobin

Hemoglobin has a quaternary structure characteristic of many multi-subunit globular proteins. This structure comes from its four subunits arranged roughly in a tetrahedral pattern.

HbA: In adult humans, the most common hemoglobin type is a tetramer (which contains 4 subunit proteins) called hemoglobin A, consisting of two alpha and beta subunits non-covalently bound, each made of 141 and 146 amino acid residues, respectively. This is denoted as alpha_2beta2. The subunits are structurally similar and about the same size. Hemoglobin A is the most intensively studied of the hemoglobin molecules.

HbF: In human infants, the hemoglobin molecule is made up of 2 alpha chains and 2 gamma chains. The gamma chains are gradually replaced by beta chains as the infant grows. Hemoglobin F has a higher oxygen affinity and in normal adults  it is restricted to a limited population of red cells called F-cells. However, the level of Hb F can be elevated in certain diseases like sickle cell or thalassaemia.

HbA2: (alpha_2delta2) – delta chain synthesis begins late in the third trimester and in adults, it has a normal range of 1.5-3.5%.

Hb in the Embryo: 

• Gower 1
• Gower 2
• Hemoglobin Portland

Hemoglobin Variant that cause disease:

• Hemoglobin H (beta₄) – A variant form of hemoglobin, formed by a tetramer of beta chains, which may be present in variants of alpha thalassemia. Continue reading »

Many blood products are available but they have never been safe as they can transmit diseases. For this reason children should only recieve blood products when othe conservative measures have failed.

Red Blood Cells ( RBCs )

Indicated in cases of severe anemia usually when Hb is < 7  gm%. or when there is acute , severe, traumatic blood loss.

Different types include:

• Whole Blood ( rarely used )
• Packed RBCs = whole blood less 70% of plasma , most commonly used
• Leukocyte poor RBCs= for pateints with history of febrile reaction to blood products or who will recieve many transfusions
• Washed RBCs = to prevent host-versus graft disease in Ig A deficient recepients

Platelets

Used when there is a potential for a clotting disorder due to thrombocytopenia ( platelets<10,000 or < 20,000 when surgery is planned ). indicated also in cases of clinically significant quantitative platelet defect.

Plasma

Available products include:

• Fresh frozen plsma (FFP )
• Single donor palsma

Indicated when there is an intravascular fluid depletion, not responsive to crystalloid or bleeding due to depletion of clotting factors.

Clotting Factor Concentrate

• Cryoprecipitate has high levels of factor VIII, von willebrand factor and fibrinogen Continue reading »