hemoglobin

Hemoglobin (Hb)
Hemoglobin (Hb) is the standard abbreviation for hemoglobin, the oxygen-carrying pigment and predominant protein in the red blood cells.

Hemoglobin carries oxygen from places of high oxygen pressure (lungs) to places of low oxygen pressure (tissues), where it readily releases the oxygen. Hemoglobin also returns CO2 from the tissues to the lungs.
A hemoglobin molecule consists of 1 molecule of globin and 4 molecules of heme (each containing 1 molecule of iron in the ferrous state).
“Globin" consists of four polypeptide chains: two alpha chains, each with 141 amino acids and two beta chains, each with 146 amino acids.

The ? and ? globin chains are very similar in structure and each one of them is linked with a heme molecule. Each heme group can combine with 1 molecule of oxygen or CO2.
A heme group is a flat ring molecule containing carbon, nitrogen and hydrogen atoms, with a single Fe2+ ion at the center. Without the iron, the ring is called a porphyrin.
Normal Ranges
In the very common laboratory tests for hemoglobin (Hb), it is measured as total hemoglobin and the result is expressed as the amount of hemoglobin in grams (gm) per deciliter (dl) of whole blood, a deciliter being 100 milliliters.
The Normal Ranges For Hemoglobin Depend On:
The age.
Altitude
The sex of the person.
Normal values in an adult are 12 to 18 grams per deciliter (100 milliliters) of blood.

Secondary polycythemia which is may be due to:
Dehydration (sever burns, diarrhea, vomitting, …etc.).
Severe lung or heart disease.
Living at high altitudes.
Heavy smoking.
Primary polycythemia which is due malignant variation in blood cells production in bone marrow
Iron deficiency or deficiencies in essential vitamins of other elements, such as B12, folate, B6.
Inherited hemoglobin defects, such as sickle cell anemia or Thalassemia.
Other inherited defects affecting the red blood cells.
Excessive bleeding.
Excessive destruction of red blood cells.
Kidney disease.
Bone marrow failure or aplastic anemia.
Cancers that affect the bone marrow.