Anemia

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Anemia (anaemia and anæmia; from ancient Greek, meaning lack of blood) is a decrease in number of Red Blood Cell (RBCs) or less than the Normal Quantity of hemoglobin in the blood.  However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of Hemoglobin Deficiency.
Because hemoglobin (found inside RBCs) normally carries Oxygen from the lungs to the tissues, Anemia leads to hypoxia (lack of oxygen) in organs. Since all human cells depend on Oxygen for survival, varying degrees of anemia can have a wide range of clinical consequences.
Anemia is the most common disorder of the blood.
The three main classes include excessive blood loss (acutely such as a hemorrhage or chronically through low-volume loss), excessive blood cell destruction (hemolysis) or deficient red blood cell production (ineffective hematopoiesis).

WHO's Hemoglobin thresholds used to define ANEMIA (1 g/dL = 0.6206 mmol/L)
Age or gender group	Hb threshold (g/dl)	Hb threshold (mmol/l)
Children (0.5–5.0 yrs)	11.0	6.8
Children (5–12 yrs)	11.5	7.1
Teens (12–15 yrs)	12.0	7.4
Women, non-pregnant (>15yrs)	12.0	7.4
Women, pregnant	11.0	6.8
Men (>15yrs)	13.0	8.1

Treatments

Treatments for anemia depend on severity and cause.

Oral Iron :          Iron deficiency from nutritional causes is rare in men and postmenopausal women. The diagnosis of iron deficiency mandates a search for potential sources of loss, such as gastrointestinal bleeding from ulcers or colon cancer. Mild to moderate iron-deficiency anemia is treated by oral iron supplementation with ferrous sulfate, ferrous fumarate, or ferrous gluconate. When taking iron supplements, stomach upset and/or darkening of the feces are commonly experienced. The stomach upset can be alleviated by taking the iron with food; however, this decreases the amount of iron absorbed. Vitamin C aids in the body's ability to absorb iron, so taking oral iron supplements with orange juice is of benefit.

Parenteral Iron : In cases where oral iron has either proven ineffective, would be too slow (for example, pre-operatively) or where absorption is impeded (for example in cases of inflammation), parenteral iron can be used. The body can absorb up to 6 mg iron daily from the gastrointestinal tract. In many cases the patient has a deficit of over 1,000 mg of iron which would require several months to replace. This can be given concurrently with erythropoietin to ensure sufficient iron for increased rates of Erythropoiesis.

Transfusions :    Doctors attempt to avoid blood transfusion in general, since multiple lines of evidence point to increased adverse patient clinical outcomes with more intensive transfusion strategies. The physiological principle that reduction of oxygen delivery associated with anemia leads to adverse clinical outcomes is balanced by the finding that transfusion does not necessarily mitigate these adverse clinical outcomes. Blood does have risks associated, such as disease transmission and host incompatibility, even in cases where crossmatching was correctly undertaken. Each unit of blood is only equivalent to 200–250 mg iron, thus requiring several units per patient to replete iron stores. Increasingly, physicians are using parenteral iron both to conserve a finite resource, for improved patient outcomes but also to reduce costs to the hospital.

Hyperbaric O_{2 :}    Treatment of exceptional blood loss (anemia) is recognized as an indication for hyperbaric oxygen (HBO) by the Undersea and Hyperbaric Medical Society.^[31][32] The use of HBO is indicated when oxygen delivery to tissue is not sufficient in patients who cannot be given blood transfusions for medical or religious reasons. HBO may be used for medical reasons when threat of blood product incompatibility or concern for transmissible disease are factors. The beliefs of some religions (ex: Jehovah's Witnesses) may require they use the HBO method.

Vitamin supplements given orally (folic acid) or intramuscularly (vitamin B₁₂) will replace specific deficiencies.