Hemoglobin is the red blood cell protein that carries oxygen to the tissues and is responsible for the red colour of blood. A deficiency in hemoglobin and in red blood cells (anemia) is manifested by weakness or fatigue, lack of energy, fainting, paleness and shortness of breath. Conversely, excess hemoglobin and red blood cells (polyglobulia) can manifest as vision problems, dizziness, headache, flushing, etc. People who live in higher altitudes generally have higher hemoglobin levels, whereas levels tend to be slightly lower in older men, women, children and pregnant women.
Hemoglobin is a complex protein normally composed of four subunits or chains (hemoglobin A) in adults: a pair of “alpha” chains and a pair of “beta” chains. The composition of each type of chain is programmed by the DNA of the chromosomes. Some people carry mutations that can either change the structure of hemoglobin and limit its capacity to carry oxygen, or unbalance the production of one type of chain and affect the total amount of hemoglobin available.
Hemoglobin results are interpreted in light of other blood count parameters (see sections on red blood cells, platelets, MCV).