Question

What is haemoglobin? What happens when haemoglobin levels decrease?

Answer 1

Haemoglobin (Hb or Hgb) is the protein molecule in red blood cells that carries oxygen from the lungs to the body's tissues and returns carbon dioxide from the tissues back to the lungs. Hemoglobin is made up of four protein molecules (globulin chains) that are connected together.
If haemoglobin level decreases, the oxygen carrying capacity of blood decreases which leads to hypoxia, anemia etc.