Hemoglobin is a protein attached to red blood cells that transports oxygen from the lungs to other organs and tissues of the body. The hemoglobin (Hb) molecule consists of 4 polypeptide chains, each with an oxygen-binding site. There are several types of hemoglobin, which differ in the structure of their polypeptide chains.
Types of Hemoglobin:
HbA (Hemoglobin A):
- Composed of two α-chains and two β-chains.
- The predominant form in healthy adults, accounting for over 96% of total hemoglobin.
HbA2 (Hemoglobin A2):
- Composed of two α-chains and two δ-chains.
- Normally comprises 2.5–3.0% of total hemoglobin.
HbF (Fetal Hemoglobin):
- Composed of two α-chains and two γ-chains.
- Predominates during fetal development but rapidly decreases in the first year of life, accounting for less than 2% in adults.
- Avoid alcohol consumption 24 hours before the test.
- Refrain from eating for 4 hours before the test; plain, non-carbonated water is allowed. For infants, the test should be done before their next feeding.
- Minimize physical and emotional stress for 30 minutes prior to the test.
Hemoglobin electrophoresis is performed in the following cases:
- Investigation of hemoglobinopathies.
- Screening for thalassemia.
- Congenital hemoglobin disorders, such as sickle cell anemia.
- Diagnosis of causes for microspherocytosis, sickle-shaped red blood cells, or hemolytic anemia.
- Symptoms such as fatigue, weakness, pallor, jaundice, growth delay in children, or painful cramps (indicative of sickle cell anemia).
- History of miscarriages.
Hemoglobinopathies and/or most thalassemias are associated with changes in the proportions of normal hemoglobin fractions such as HbA, HbA2, and HbF. In hemoglobinopathies, pathological fractions representing abnormal protein types may also be detected. The most commonly encountered structurally altered hemoglobin variants are HbS, HbD, HbE, and HbC. The HbS variant holds the greatest clinical significance as it leads to the manifestations of sickle cell anemia.
Conditions Associated with Hemoglobin Changes:
Increased HbF Levels:
- Observed during pregnancy (beyond neonates).
- Associated with hereditary hemoglobin disorders:
- Beta-thalassemia.
- Hereditary persistence of fetal hemoglobin (HPFH).
- Sickle cell anemia.
Acquired Disorders:
- Megaloblastic anemia (e.g., pernicious anemia).
- Sideroblastic anemia.
- Aplastic anemia.
- Myelofibrosis.
- Leukemia.
- Benign monoclonal gammopathies.
- Chronic kidney disease (CKD).
- Hyperthyroidism.
- Cancer with bone marrow metastases.