What is anemia?

Understanding Anemia: Definition, Classification, Causes, and Management

Definition and Classification of Anemia

Anemia is defined as a reduction of the hemoglobin (Hb) concentration, red-cell count, or packed cell volume below normal levels. 1

• Anemia is diagnosed when hemoglobin levels fall below:

  • <13.5 g/dL in adult males 1
  • <12.0 g/dL in adult females 1
  • These thresholds may vary slightly according to different guidelines, with some defining anemia as <13.0 g/dL in men and <12.0 g/dL in women 2

• Anemia severity is classified as 1:

  • Mild: Hb ≥10 g/dL and ≤11.9 g/dL
  • Moderate: Hb ≥8.0 g/dL and ≤9.9 g/dL
  • Severe: Hb <8.0 g/dL

Epidemiology of Anemia

• Anemia affects approximately one-third of the world's population 3
• In cancer patients, anemia of chronic disease is present in about 40% of cases 1
• In heart failure patients, anemia prevalence increases with disease severity, affecting 25-40% of patients 1
• Anemia is more common in women, elderly people, and patients with chronic diseases 1, 3
• In children, iron deficiency anemia has an incidence of 20.1% between 0-4 years in industrialized countries 4

Etiology and Pathophysiology

Anemia can result from three main mechanisms 5:

1. Blood loss (acute or chronic) 4, 5:

   • Gastrointestinal bleeding
   • Heavy menstrual bleeding
   • Trauma
   • Surgical procedures

2. Decreased red blood cell production 5:

   • Iron deficiency (most common cause worldwide) 4, 3
   • Vitamin B12 or folate deficiency 1
   • Chronic kidney disease 1
   • Bone marrow disorders
   • Chronic inflammation

3. Increased red blood cell destruction 5:

   • Hemolytic anemias
   • Genetic disorders (thalassemia, sickle cell disease)
   • Autoimmune conditions

Specific Types of Anemia

Iron Deficiency Anemia (IDA)

• Most common type of anemia worldwide 4, 3
• Caused by inadequate iron intake, poor absorption, or blood loss 4
• Diagnosis confirmed by 1:
  • Low serum ferritin (<30 μg/L without inflammation)
  • Low transferrin saturation (<16%)
  • In presence of inflammation, ferritin <100 μg/L suggests iron deficiency

Anemia of Chronic Disease (ACD)

• Second most common cause of anemia 1
• Associated with chronic inflammatory conditions, infections, cancer 1
• Diagnostic criteria include 1:
  • Serum ferritin >100 μg/L
  • Transferrin saturation <16%
  • Evidence of underlying chronic disease

Anemia in Heart Failure

• Present in 25-40% of heart failure patients 1
• Associated with increased mortality risk (approximately doubled) 1
• Causes include iron deficiency, renal dysfunction, and chronic inflammation 1
• Negatively impacts exercise capacity and quality of life 1

Anemia in Cancer

• Prevalence varies by cancer type (highest in lung and gynecological cancers) 1
• Causes include chemotherapy-induced bone marrow suppression, bleeding, nutritional deficiencies, and chronic inflammation 1
• Significantly impacts quality of life and may affect treatment outcomes 1

Diagnostic Approach

Initial Evaluation

• Complete blood count (CBC) with red cell indices 1
• Reticulocyte count to assess bone marrow response 1
• Iron studies (serum iron, ferritin, transferrin saturation) 1
• Vitamin B12 and folate levels 1
• Inflammatory markers (C-reactive protein) 1
• Renal function tests 1
• Peripheral blood smear examination 1

Additional Testing Based on Clinical Suspicion

• Bone marrow examination when indicated 1
• Assessment for occult blood loss in stool and urine 1
• Coombs testing in suspected hemolytic anemia 1
• Hemoglobin electrophoresis for suspected hemoglobinopathies 5
• Endogenous erythropoietin levels in suspected myelodysplasia 1

Management Principles

Iron Deficiency Anemia

• Oral iron supplementation is first-line therapy 1, 4
• Intravenous iron may be necessary in cases of poor absorption, intolerance to oral iron, or when rapid correction is needed 1
• In patients with iron deficiency anemia having elective non-cardiac surgery, preoperative iron therapy (oral or IV) is reasonable to reduce blood transfusions and increase hemoglobin 1
• Identify and treat the underlying cause (e.g., GI bleeding, heavy menstrual bleeding) 4

Anemia in Heart Failure

• Treatment of anemia in heart failure patients may improve quality of life and functional capacity 1
• Iron deficiency should be corrected even in the absence of anemia 1
• Consider erythropoiesis-stimulating agents in selected cases 1

Anemia in Cancer

• Erythropoiesis-stimulating agents (ESAs) may be considered in chemotherapy-induced anemia 1
• Blood transfusions for severe symptomatic anemia 1
• Iron supplementation when iron deficiency is present 1

Blood Transfusions

• Generally reserved for severe symptomatic anemia or acute blood loss 1
• Restrictive transfusion threshold (Hb <8 g/dL) is recommended for most patients 1
• Transfusion threshold of 7 g/dL may be appropriate in stable patients 1
• Higher thresholds may be considered in patients with acute coronary syndrome 1

Prevention Strategies

• Regular screening for high-risk populations 1
• Iron supplementation during pregnancy 1
• Nutritional education and iron-rich diet promotion 1
• Prompt treatment of conditions that may lead to blood loss 4
• Regular monitoring of hemoglobin levels in patients with chronic diseases 1

Special Considerations

Anemia in Pregnancy

• Physiologic hemodilution causes a natural decline in hemoglobin during pregnancy 1
• Iron requirements increase significantly during pregnancy 1
• High hemoglobin (>15.0 g/dL) in the second trimester may indicate poor blood volume expansion and is associated with adverse outcomes 1

Anemia in the Elderly

• Often multifactorial (nutritional deficiencies, chronic disease, unexplained anemia) 2
• Associated with increased morbidity and mortality 2
• Unexplained anemia accounts for approximately one-third of cases in the elderly 2

Anemia in Chronic Kidney Disease

• Prevalence increases with declining kidney function 1
• Regular surveillance of hemoglobin levels is recommended 1
• Treatment may include iron supplementation and erythropoiesis-stimulating agents 1