Anemia

Anemia is a blood disorder in which the blood has a reduced ability to carry oxygen. This can be due to a lower than normal number of red blood cells, a reduction in the amount of hemoglobin available for oxygen transport, or abnormalities in hemoglobin that impair its function. The name is derived.
When anemia comes on slowly, the symptoms are often vague, such as tiredness, weakness, shortness of breath, headaches, and a reduced ability to exercise. When anemia is acute, symptoms may include confusion, feeling like one is going to pass out, loss of consciousness, and increased thirst. Anemia must be significant before a person becomes noticeably pale. Additional symptoms may occur depending on the underlying cause. Anemia can be temporary or long-term and can range from mild to severe.
Anemia can be caused by blood loss, decreased red blood cell production, and increased red blood cell breakdown. Causes of blood loss include menstruation, bleeding due to inflammation of the stomach or intestines, bleeding from surgery, serious injury, or blood donation. Causes of decreased production include iron deficiency, folate deficiency, vitamin B₁₂ deficiency, thalassemia and a number of bone marrow tumors. Causes of increased breakdown include genetic disorders such as sickle cell anemia, infections such as malaria, and certain autoimmune diseases like autoimmune hemolytic anemia.
Anemia can also be classified based on the size of the red blood cells and amount of hemoglobin in each cell. If the cells are small, it is called microcytic anemia; if they are large, it is called macrocytic anemia; and if they are normal sized, it is called normocytic anemia. The diagnosis of anemia in men is based on a hemoglobin of less than 130 g/L; in non-pregnant women, it is less than 120 g/L, while in pregnant women it is less than 105–110. Further testing is then required to determine the cause.
Treatment depends on the specific cause. Certain groups of individuals, such as pregnant women, can benefit from the use of iron pills for prevention. Dietary supplementation, without determining the specific cause, is not recommended. The use of blood transfusions is typically based on a person's signs and symptoms. In those without symptoms, they are not recommended unless hemoglobin levels are less than 60 to 80 g/L. These recommendations may also apply to some people with acute bleeding. Erythropoiesis-stimulating agents are only recommended in those with severe anemia.
Anemia is the most common blood disorder, affecting about a fifth to a third of the global population. Iron-deficiency anemia is the most common cause of anemia worldwide, and affects nearly one billion people. In 2013, anemia due to iron deficiency resulted in about 183,000 deaths – down from 213,000 deaths in 1990. This condition is most prevalent in children with also an above average prevalence in elderly and women of reproductive age. Anemia is one of the six WHO global nutrition targets for 2025 and for diet-related global targets endorsed by World Health Assembly in 2012 and 2013. Efforts to reach global targets contribute to reaching Sustainable Development Goals, with anemia as one of the targets in SDG 2 for achieving zero world hunger.

Signs and symptoms

Symptoms of anemia can come on quickly or slowly. Early on there may be few or no symptoms. If the anemia continues slowly, the body may adapt and compensate for this change. In this case, no symptoms may appear until the anemia becomes more severe. Symptoms can include feeling tired, weak, dizziness, headaches, shortness of breath, difficulty concentrating, irregular or rapid heartbeat, easy bleeding or bruising, cold hands and feet, pale or yellow skin, and muscle weakness.
Anemia that develops quickly, often, has more severe symptoms, including, feeling faint, chest pain, sweating, increased thirst, and confusion. There may be also additional symptoms depending on the underlying cause.
In more severe anemia, the body may compensate for the lack of oxygen-carrying capability of the blood by increasing cardiac output. The person may have symptoms related to this, such as palpitations, angina, intermittent claudication of the legs, and symptoms of heart failure.
Severe anemia can cause pallor, such as pale skin or other parts of the body. Pale skin may be visible in hand palms and fingernails beds. Other locations to detect pallor are the inner lining of the lower eyelid and the tongue. Many people with mild anemia do not show pallor.
Iron-deficiency anemia may give symptoms that can include spoon-shaped nails, restless legs syndrome, and pica. A blue coloration of the sclera may be noticed in some cases of iron-deficiency anemia. Vitamin B₁₂ deficiency anemia may result in decreased ability to think, memory loss, confusion, personality or mood changes, depression, difficulty walking, blurred vision, and irreversible nerve damage. Other specific causes of anemia may have signs and/or complications such as, jaundice with the rapid break down of red blood cells as with hemolytic anemia, bone abnormalities with thalassemia major, or leg ulcers as seen in sickle cell disease.
In severe anemia, there may be signs of a hyperdynamic circulation: tachycardia, bounding pulse, flow murmurs, and cardiac ventricular hypertrophy. There may be signs of heart failure.
Pica, the consumption of non-food items such as ice, paper, wax, grass, hair or dirt, may be a symptom of iron deficiency; although it occurs often in those who have normal levels of hemoglobin. Chronic anemia may result in behavioral disturbances in children as a direct result of impaired neurological development in infants, and reduced academic performance in children of school age. Restless legs syndrome is more common in people with iron-deficiency anemia than in the general population.

Causes

The causes of anemia may be classified as impaired red blood cell production, increased RBC destruction, blood loss, and fluid overload. Several of these may interplay to cause anemia. The most common cause of anemia is blood loss, but this usually does not cause any lasting symptoms unless a relatively impaired RBC production develops, in turn, most commonly by iron deficiency.

Impaired production

Disturbance of proliferation and differentiation of stem cells
* Pure red cell aplasia
* Aplastic anemia affects all kinds of blood cells. Fanconi anemia is a hereditary disorder or defect featuring aplastic anemia and various other abnormalities, including malformation of the extremities.
* Anemia of kidney failure due to insufficient production of the hormone erythropoietin
* Anemia of endocrine disease
Disturbance of proliferation and maturation of erythroblasts
* Pernicious anemia is a form of megaloblastic anemia due to vitamin B₁₂ deficiency dependent on impaired absorption of vitamin B₁₂. Lack of dietary B₁₂ causes non-pernicious megaloblastic anemia.
* Anemia of folate deficiency, as with vitamin B₁₂, causes megaloblastic anemia
* Anemia of prematurity, by diminished erythropoietin response to declining hematocrit levels, combined with blood loss from laboratory testing, generally occurs in premature infants at two to six weeks of age.
* Iron-deficiency anemia, resulting in deficient heme synthesis. In anemia among older patients, diet alone is rarely the issue; iron loss from the gastrointestinal tract, impaired absorption, chronic inflammation and kidney disease often coexist. Excessive cow milk consumption is a common cause of iron deficiemcy anemia in young children.
* Thalassemias, causing deficient globin synthesis
* Congenital dyserythropoietic anemias, causing ineffective erythropoiesis
* Anemia of kidney failure
Other mechanisms of impaired RBC production
* Myelophthisic anemia or myelophthisis is a severe type of anemia resulting from the replacement of bone marrow by other materials, such as malignant tumors, fibrosis, or granulomas.
* Myelodysplastic syndrome
* anemia of chronic inflammation
* Leukoerythroblastic anemia is caused by space-occupying lesions in the bone marrow that prevent normal production of blood cells.
General Global contributors
*In many regions, nutritional deficiencies are major drivers of reduced RBC production. Poor intake of iron, folate, and vitamin B₁₂ can significantly impair hemoglobin synthesis and erythropoiesis. This is especially common in low-income populations, areas with limited food diversity, and communities experiencing famine.
*Pregnancy greatly increases iron requirements, and inadequate dietary intake during pregnancy is one of the leading causes of anemia among reproductive-age women worldwide.
*Chronic infections common in developing countries, such as malaria and hookworm disease, impair erythropoiesis either through inflammatory suppression or recurrent blood loss leading to iron depletion.
*Socioeconomic factors such as poverty, limited access to nutrient-rich foods, and high rates of parasitic exposure increase the risk of iron-deficiency anemia in women and children.
Anemia of chronic disease
*Chronic inflammatory conditions can inhibit iron mobilization and impair the bone marrow's ability to produce RBC count. This mechanism is a major cause of anemia in developed countries and frequently coexists with other types of anemia.

Chronic inflammation can disrupt iron handling limiting its availability for red blood cell formation. During inflammatory states, the liver produces high levels of hepcidin, a hormone that blocks iron release from intestinal cells and macrophages. This leads to high ferritin levels and low transferrin saturation, a pattern known as "functional iron deficiency." This mechanism is commonly seen in older hospitalized patients with long-standing illnesses such as infections, heart failure or autoimmune conditions.