Anemia – colloquially called anemia – (synonyms: Blood deficiency; from Greek αν- an- for negation: “un-“, “without” and αἷμα haíma “blood”; ICD-10-GM D64.9: Anemia, unspecified) is an excessively low proportion of erythrocytes (red blood cells) in the blood volume (hematocrit) below specified reference values. This is associated with a reduction in the hemoglobin content of the blood below the age- and sex-specific norm.
For standard values of erythrocytes and hemoglobin, see the topics of the same name.
WHO definition of anemia:
- Hb < 13.0 g/dl in men > 15 years and postmenopausal women* .
- Hb < 12.0 g/dl in females of fertile age > 15 years*
- Hb < 11.0 g/dl in pregnant women
* also applies to geriatric patients
Degree of anemia:
- Low-grade anemia: Hb between 10 g/dL and the lower value of the normal range.
- Moderate-grade anemia: Hb 8-10 g/dl.
- High-grade anemia: Hb < 8 g/dl.
Anemias are classified by:
- Hemoglobin content (MCH) per erythrocyte: hyper-, normo-, hypochromic anemia.
- Red blood cell size (MCV): macro-, normo-, microcytic anemia.
- Shape of the erythrocytes (eg, spherocytic anemia, sickle cell anemia).
- Appearance of erythrocyte precursors in the peripheral blood (megaloblastic anemia).
For details, see classification.
Pathophysiologic differentiation of anemias:
- Hyporegeneration
- Disturbed maturation
- Hemolysis
- Hemorrhage*
* Note: In acute bleeding anemia, Hb concentration is initially normal and only drops significantly after volume replacement therapy.
Classification of anemias by etiology (causes):
- Bleeding (chronic, acute).
- Erythropoiesis disorders
- Substrate or cofactor deficiency (e.g., iron deficiency anemia, vitamin B12 deficiency anemia, folic acid deficiency anemia).
- Chronic diseases (anemia associated with chronic disease).
- Renal failure (renal anemia)
- Infections (infectious anemia)
- Tumors (tumor anemia)
- Anemia due to metastatic malignancies (tumor disease with daughter tumors).
- Anemia due to bone marrow infiltration (e.g., leukemias/blood cancers).
- Anemia as a result of increased degradation of erythrocytes – hemolytic anemia (see below hemolytic anemia).
Anemia can be a symptom of many diseases (see under “Differential diagnoses”).
The prevalence (disease frequency) of anemia is 25% of the population worldwide.
Course and prognosis: course and prognosis depends on the diagnosis or underlying disease. Note: In old age, anemia is never physiologic (“natural,” “healthy”)!
