ANEMIA

Epidemiology

Occurrence in the United States

The prevalence of anemia in population studies of healthy, nonpregnant people depends on the Hb concentration chosen for the lower limit of normal values. The World Health Organization (WHO) chose 12.5 g/dL for both adult males and females. In the United States, limits of 13.5 g/dL for men and 12.5 g/dL for women are probably more realistic. Using these values, approximately 4% of men and 8% of women have values lower than those cited. A significantly greater prevalence is observed in patient populations. Less information is available regarding studies using RBC or Hct.

International occurrence

The prevalence of anemia in Canada and northern Europe is believed to be similar to that in the United States. In underprivileged countries, limited studies of purportedly healthy subjects show the prevalence of anemia to be 2-5 times greater than that in the United States. Although geographic diseases, such as sickle cell anemia, thalassemia, malaria, hookworm, and chronic infections, are responsible for a portion of the increase, nutritional factors with iron deficiency and, to a lesser extent, folic acid deficiency play major roles in the increased prevalence of anemia. Populations with little meat in the diet have a high incidence of iron deficiency anemia, because heme iron is better absorbed from food than inorganic iron.

Sickle cell disease is common in regions of Africa, India, Saudi Arabia, and the Mediterranean basin. The thalassemias are the most common genetic blood diseases and are found in Southeast Asia and in areas where sickle cell disease is common.

Race-related demographics

Certain races and ethnic groups have an increased prevalence of genetic factors associated with certain anemias. Diseases such as the hemoglobinopathies, thalassemia, and G-6-PD deficiency have different morbidity and mortality in different populations due to differences in the genetic abnormality producing the disorder. For example, G-6-PD deficiency and thalassemia have less morbidity in African Americans than in Sicilians because of differences in the genetic fault. Conversely, sickle cell anemia has greater morbidity and mortality in African Americans than in Saudi Arabians.

Race is a factor in nutritional anemias and anemia associated with untreated chronic illnesses to the extent that socioeconomic advantages are distributed along racial lines in a given area;  socioeconomic advantages that positively affect diet and the availability of health care lead to a decreased prevalence of these types of anemia. For instance, iron deficiency anemia is much more prevalent in the populations of developing nations, who tend to have little meat in their diets, than it is in populations of the United States and northern Europe.

Similarly, anemia of chronic disorders is commonplace in populations with a high incidence of chronic infectious disease (eg, malaria, tuberculosis, acquired immunodeficiency syndrome [AIDS]), and this is at least in part worsened by the socioeconomic status of these populations and their limited access to adequate health care.

Sex-related demographics

Overall, anemia is twice as prevalent in females as in males. This difference is significantly greater during the childbearing years due to pregnancies and menses.

Approximately 65% of body iron is incorporated into circulating Hb. One gram of Hb contains 3.46 mg of iron (1 mL of blood with an Hb concentration of 15 g/dL = 0.5 mg of iron). Each healthy pregnancy depletes the mother of approximately 500 mg of iron. While a man must absorb about 1 mg of iron to maintain equilibrium, a premenopausal woman must absorb an average of 2 mg daily. Further, because women eat less food than men, they must be more than twice as efficient as men in the absorption of iron to avoid iron deficiency.

Women have a markedly lower incidence of X-linked anemias, such as G-6-PD deficiency and sex-linked sideroblastic anemias, than men do. In addition, in the younger age groups, males have a higher incidence of acute anemia from traumatic causes.

Age-related demographics

Previously, severe, genetically acquired anemias (eg, sickle cell disease, thalassemia, Fanconi syndrome) were more commonly found in children because they did not survive to adulthood. However, with improvement in medical care and breakthroughs in transfusion and iron chelation therapy, in addition to fetal hemoglobin modifiers, the life expectancy of persons with these diseases has been significantly prolonged. 

Acute anemia has a bimodal frequency distribution, affecting mostly young adults and persons in their late fifties. Causes among young adults include trauma, menstrual and ectopic bleeding, and problems of acute hemolysis. During their childbearing years, women are more likely to become iron deficient.

In people aged 50-65 years, acute anemia is usually the result of acute blood loss in addition to a chronic anemic state. This is the case in uterine and GI bleeding.

Neoplasia increases in prevalence with each decade of life and can produce anemia from bleeding, from the invasion of bone marrow with tumor, or from the development of anemia associated with chronic disorders. The use of aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), and warfarin also increases with age and can produce GI bleeding.