Haemoglobin

Function

Haemoglobin (Hb) is the iron-containing protein found within red blood cells (RBCs). Its primary function is the transport of oxygen from the lungs to the body's tissues and the transport of carbon dioxide from the tissues back to the lungs. Each haemoglobin molecule can bind four oxygen molecules, a process facilitated by the presence of heme groups.

Why it is Ordered

The haemoglobin test is one of the most common medical tests, usually performed as part of a Complete Blood Count (CBC). It is ordered to:

• Screen for Anemia: Detecting a low oxygen-carrying capacity.
• Evaluate Fatigue: Investigating symptoms of weakness or shortness of breath.
• Monitor Chronic Disease: Checking patients with kidney disease or inflammatory conditions.
• Assess Blood Loss: Monitoring patients after surgery or trauma.
• Check Polycythemia: Screening for overproduction of RBCs.

Associated Conditions

• Iron Deficiency Anemia: The most common cause of low Hb globally.
• Vitamin B12/Folate Deficiency: Leads to megaloblastic anemia.
• Chronic Kidney Disease: Reduced erythropoietin production.
• Sickle Cell Disease and Thalassemia: Genetic disorders affecting Hb structure or production.
• Polycythemia Vera: A bone marrow disorder causing excess RBC production.

Interpretation

Low haemoglobin levels (anemia) indicate that the body's tissues may not be receiving adequate oxygen, leading to clinical symptoms like pallor and tachycardia. High levels (polycythemia) can increase blood viscosity, raising the risk of clots and strokes. Interpreting Hb requires looking at other indices like MCV (Mean Corpuscular Volume) to determine the 'type' of anemia present.