Anemia: General Considerations

How to Cite This Chapter: Crowther M, Podolak-Dawidziak M. Anemia: General Considerations. McMaster Textbook of Internal Medicine. Kraków: Medycyna Praktyczna. Accessed July 07, 2020.
Last Updated: May 8, 2019
Last Reviewed: May 8, 2019
Chapter Information


Anemia is defined as a decrease in hemoglobin levels (Hb), hematocrit values (Ht), and red blood cell (RBC) counts.

Classification based on the severity of anemia:

1) Mild anemia: Hb 10 to 12 g/dL in women and to 13.5 g/dL in men.

2) Moderate anemia: Hb 8 to 9.9 g/dL.

3) Severe anemia: Hb 6.5 to 7.9 g/dL.

4) Life-threatening anemia: Hb <6.5 g/dL.

Causes: Loss of RBCs due to hemorrhage (acute or chronic), hemolysis, sequestration, or impaired erythropoiesis.

Systemic manifestations are independent of the cause and type of anemia. They include weakness, fatigue, concentration and attention deficits, headache, dizziness/vertigo, tachycardia and dyspnea (in severe anemia), and pallor of the skin and mucous membranes (or jaundice in hemolytic anemia). In severe cases manifestations of systemic hypoxia lead to cardiovascular collapse, acidosis, and death.

RBC parameters (Table 7.1-1) may be used for the initial differentiation between the causes of anemia.


Table 7.1-1. Classification of anemias based on the reticulocyte count, mean corpuscular volume, and red cell distribution width



RC ≥100,000/microL

RC <100,000/microL

Microcytic MCV ↓


Beta thalassemia

Anemia of chronic disease (some cases)

Beta thalassemia

– Iron deficiency anemia

– Inherited sideroblastic anemia (some cases)

Normocytic MCV (N)


– Anemia of chronic disease (most cases)

– Anemia in chronic kidney disease

– Aplastic anemia

– Anemia due to acute blood loss

– Most of hemolytic anemias

– Early stage of iron deficiency anemia

– Cobalamin or folate deficiency

– Mixed-type anemia (eg, combined iron and cobalamin deficiency)

– Myelodysplastic syndrome

Macrocytic MCV ↑


Chronic liver disease

– Chemotherapy

– Alcohol dependency

– Aplastic anemia

– Some autoimmune hemolytic anemias (due to reticulocytosis)

– Chronic liver disease

– Cobalamin or folate deficiency

– Myelodysplastic syndrome

↑, increased; ↓, decreased; MCV, mean corpuscular volume; N, normal; RC, reticulocyte count; RDW, red cell distribution width.

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