- Author: Christopher D Braden, DO; Chief Editor: Barry E Brenner, MD, PhD, FACEP more...
Anemia is defined as an absolute reduction in the quantity of the oxygen-carrying pigment hemoglobin (Hgb) in the circulating blood. Anemia is further broadly subcategorized into acute and chronic. (See Etiology.)
Anemia usually is grouped into 3 etiologic categories: decreased red blood cell (RBC) production, increased RBC destruction, and blood loss.
Anemia is a manifestation of an underlying disease process and is not a diagnosis in itself. A wide array of diseases, including inflammations, infections, and malignancies, may at some point be associated with anemia. Common conditions associated with anemia include the following:
Gastric or duodenal ulcer
Liver or renal disease
Sickle cell disease
Previous history of anemia or blood transfusions
Thrombocytopenia or blood coagulation disorders
Cancer or other chronic illness (eg, rheumatic disease)
Poor diet, especially iron deficiency
A disease may lead to anemia through a combination of mechanisms. For example, a GI malignancy may cause anemia through blood loss, as well as lead to anemia of chronic disease. (See Etiology.)
For patient education information, see Anemia.
Microcytic hypochromic anemia
Possible causes of this condition include iron deficiency, thalassemia, sideroblasts, and lead poisoning.
Anemia of chronic disease commonly is manifested by normocytic normochromic indices; however, microcytic hypochromic indices also can be associated with anemia of chronic disease.
Possible causes of macrocytic anemia include vitamin B-12 deficiency, folate deficiency, liver disease, and hypothyroidism.
Normocytic anemia is further divided into 2 broad categories: anemia with primary bone marrow involvement and anemia secondary to underlying disease.
The etiology of myelophthisic anemia involves interruption of normal hematopoiesis due to the accumulation of malignant or reactive cells or cell products. It is characterized by the appearance of immature myeloid cells and nucleated RBCs in the peripheral blood. The 3 major classes of disorders that can produce myelophthisic anemia are intrinsic bone marrow malignancies (eg, leukemia, lymphoma, myeloma), metastatic tumors (eg, neuroblastoma, melanoma), cancers that are more prone to bone marrow metastasis (eg, prostate, breast, lung, stomach, renal carcinomas), and granulomatous disease (eg, tuberculosis, sarcoidosis).
Agnogenic myeloid metaplasia, which is characterized by anemia with primary bone marrow involvement, involves gradual bone marrow fibrosis, extramedullary hematopoiesis, and splenomegaly with no known underlying systemic disorder.
Most cases of anemia in the world are secondary to an underlying disease. The marrow does not respond appropriately to microcytic anemia, leading to decreased production of RBCs. This type of anemia includes that associated with liver cirrhosis, uremia, chronic inflammation, and hypoendocrine conditions (eg, thyroid, adrenal, pituitary disorders).
This type of anemia includes sickle cell anemia, thrombotic thrombocytopenic purpura (TTP), hemolytic uremic syndrome, aortic valve prosthesis, disseminated intravascular coagulation (DIC), cold agglutinin disease, and paroxysmal cold hemoglobinuria (PCH).
Occurrence in the United States and internationally
The incidence of anemia mirrors the incidence of the underlying cause. Some published studies report the incidence of anemia to be 2-15% in the United States and Great Britain.
Anemia is far more common in underdeveloped countries than in the United States. The true incidence of anemia is difficult to define because of multiple factors (eg, patient population, geographic location, normal range reference, ability to adequately screen for the disease).
Among 292 children in a low-income community in the Dominican Republic, 69.9% were found to be anemic using the World Health Organization (WHO)–recommended hemoglobin cut point of <11.0 g/dl, and 34.6% were classified as anemic using a cut point of <10.0 g/dl. The prevalence of microcytosis in anemic children ranged from 23.5% to 80.2%, depending on the hemoglobin and age-based mean corpuscular volume cut points used.
Race-, sex-, and age-related demographics
African Americans have a higher incidence of sickle cell anemia and glucose-6-phosphate dehydrogenase (G-6-PD) deficiency. G-6-PD is essential for RBC protection from oxidative insults and for approximately 10% of RBC energy production.
Mediterranean populations show a higher incidence of beta thalassemia.
Sex distribution varies based on the underlying cause. Overall, females have approximately twice the incidence of males of anemia.
Anemia is prevalent in all age groups. Some younger patients may have a better ability to compensate for anemia, which may delay initial diagnosis.
Prognosis is dependent on several factors. The underlying medical condition usually dictates the prognosis, but comorbid conditions, the chronicity of the disease, and the patient’s diet, age, and access to medical care are contributing factors.
The majority of complications in chronic anemia arise from chronic or persistent tissue hypoxia.
Pediatric patients, elderly patients, and patients who are immunocompromised are at the highest risk for complications, since they have less physiologic reserve.
Failure to comply with follow-up and treatment regimens predisposes patients with chronic anemia to complications.
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