Anemia in Clinical Practice—Definition and Classification: Does Hemoglobin Change With Aging?

Anemia is a global public health problem affecting both developing and developed countries at all ages. According to the World Health Organization (WHO), anemia is defined as hemoglobin (Hb) levels <12.0 g/dL in women and <13.0 g/dL in men. However, normal Hb distribution varies not only with sex but also with ethnicity and physiological status. New lower limits of normal Hb values have been proposed, according to ethnicity, gender, and age. Anemia is often multifactorial and is not an independent phenomenon. For the classification and diagnosis the hematologic parameters, the underlying pathological mechanism and patient history should be taken into account. The aging of population, especially in Western countries, causes an increase of anemia in elderly people. In this population, anemia, recently defined by levels of Hb <12 g/dL in both sexes, is mostly of mild degree (10–12 g/dL). Understanding the pathophysiology of anemia in this population is important because it contributes to morbidity and mortality. In one third of the patients, anemia is due to nutritional deficiency, including iron, folate, or vitamin B12 deficiency; moreover, anemia of chronic disease accounts for about another third of the cases. However, in one third of patients anemia cannot be explained by an underlying disease or by a specific pathological process, and for this reason it is defined “unexplained anemia”. Unexplained anemia might be due to the progressive resistance of bone marrow erythroid progenitors to erythropoietin, and a chronic subclinical pro-inflammatory state.