Hematocrit and hemoglobin, referred to as HCT and HGB, are components of red blood cells. The Mayo Clinic defines hematocrit as the number of red blood cells in a specified amount of blood. The Mayo Clinic defines hemoglobin as a protein molecule in red blood cells that, along with iron, transports oxygen to body tissues. The causes of low hemoglobin and hematocrit, called anemia, include blood loss, dietary deficiencies and genetic disease.
Acute or chronic blood loss lowers the hematocrit and hemoglobin according to the Mayo Clinic. Acute blood loss can occur from trauma with lacerations, open wounds and fractures. It also includes surgical procedures where blood loss is expected for the procedure. Chronic blood loss may not be readily visible as in gastrointestinal bleeding from cancer of the colon or internal injuries from trauma. Chronic blood loss is also associated with the menstrual cycle for women and blood loss from stomach ulcers.
Iron Deficiency Anemia
The hematocrit and hemoglobin can decrease with iron deficiency anemia. Frequently the result of a nutritional deficit, iron deficiency leads to a decrease in red blood cells according to The National Institute of Health. A decrease in red blood cells results in less oxygen carried to body tissues. Hemoglobin relies on iron intake from dietary sources and the absorption of iron from old red blood cells. A decrease in hematocrit and hemoglobin can be a result of less iron in the diet, less iron for re-absorption or blood loss. Decreased iron absorption can occur as a result of the inappropriate use of antacids and as a result of gastric bypass surgery.
Sickle Cell Disease
Sickle cell anemia, a genetic disease, causes a defect in hemoglobin according to the Mayo Clinic. The defect causes abnormal red blood cells to have a sickle shape. The sickle shaped cells do not readily move through small vessels and can block blood flow. The result is a decrease in blood and oxygen delivered to vital organs. The consequence of less oxygen to the body causes acute pain referred to as a sickle cell crisis. Normally, red blood cells have a life span of 120 days but the life span of sickled cells is 10 to 20 days. The resulting rapid loss of red blood cells lowers the hematocrit and hemoglobin, causing anemia.