Practice Essentials
Anemia is defined as an absolute reduction in the quantity of the oxygen-carrying pigment hemoglobin (Hgb) in the circulating blood. Normal Hgb concentration varies by age and sex, as follows [1] :
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6 to 59 months: ≥ 11.0 g/dL
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5-11 years: ≥ 11.5 g/dL
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12-14 years: ≥ 12.0 g/dL
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Females 15 years and older: ≥ 12.0 g/dL
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Pregnant females: ≥ 11.0 g/dL
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Males 15 years and older: ≥ 13.0 g/dL
Anemia is further broadly subcategorized into acute and chronic. (See Etiology.)
Anemia usually is grouped into 3 etiologic categories:
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Decreased red blood cell (RBC) production
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Increased RBC destruction
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Blood loss
Anemia is a manifestation of an underlying disease process and is not a diagnosis in itself. A wide array of diseases, including inflammatory, infectious, and malignant disorders, may at some point be associated with anemia. Common conditions associated with anemia include the following:
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Gastritis
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Gastric or duodenal ulcer
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Liver or kidney disease
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Hypothyroidism
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Sickle
Etiology
Microcytic hypochromic anemia
Possible causes of this condition include the following:
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Iron deficiency
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Thalassemia
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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.
Macrocytic anemia
Possible causes of macrocytic anemia include the following:
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Vitamin B12 deficiency
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Folate deficiency
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Liver disease
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Hypothyroidism
Normocytic anemia
Normocytic anemia is further divided into 2 broad categories: anemia with primary bone marrow involvement and anemia secondary to underlying disease.
Anemias with primary bone involvement include aplastic anemia and myelophthisic anemia.
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 as follows:
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Intrinsic bone marrow malignancies (eg, leukemia, lymphoma, myeloma)
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Cancers that have metastasized to bone (eg, prostate, breast, lung, stomach, renal carcinoma, neuroblastoma, melanoma)
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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).
Hemolytic anemia
This type of anemia includes the following:
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Sickle cell anemia
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Thrombotic thrombocytopenic purpura (TTP)
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Hemolytic-uremic syndrome
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Aortic valve prosthesis
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Disseminated intravascular coagulation (DIC)
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Cold agglutinin disease
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Paroxysmal cold hemoglobinuria (PCH)
Epidemiology
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. [2]
Race-, sex-, and age-related demographics
African Americans have a higher incidence of sickle cell anemia and glucose-6-phosphate dehydrogenase (G6PD) deficiency. G6PD 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 anemia compared with males.
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
Prognosis depends on several factors. The underlying medical condition usually dictates the prognosis, but contribuing factors include the following:
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Comorbid conditions
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The chronicity of the disease
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The patient’s diet, age, and access to medical care
Surgical patients with anemia, even if mild, are at increased risk for RBC transfusion and poor clinical outcomes after surgery. The International Consensus Conference on Anemia Management in Surgical Patients (ICCAMS) recommends that all patients except those undergoing minor elective procedures should be screened for anemia preoperatively. [3]
Complications
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.
