What is the operational definition of anemia?

Operational Definition of Anemia

Anemia is operationally defined as hemoglobin (Hb) levels below 12.0 g/dL in women and below 13.0 g/dL in men, based on the longstanding WHO criteria, though recent evidence suggests these thresholds may need refinement based on age and clinical context. 1

Standard Hemoglobin Thresholds

The traditional WHO definition established in 1968 remains the most widely used operational standard in clinical practice and public health:

• Non-pregnant women: Hb <12.0 g/dL 1
• Men: Hb <13.0 g/dL 1
• Pregnant women: Hb <11.0 g/dL 1

These thresholds were originally based predominantly on Caucasian adult populations in Europe and North America. 2

Updated Evidence-Based Thresholds

The most recent and highest quality evidence from 2024 provides refined statistical thresholds (5th centiles) based on international healthy reference populations: 3

Pediatric Populations

• Ages 6-23 months: 104.4 g/L (10.4 g/dL) 3
• Ages 24-59 months: 110.2 g/L (11.0 g/dL) 3
• Ages 5-11 years: 114.4 g/L (11.4 g/dL) 3

Adolescents (12-17 years)

• Females: 122.2 g/L (12.2 g/dL) 3
• Males: 128.2 g/L (12.8 g/dL) 3

Adults (18-65 years)

• Non-pregnant females: 119.7 g/L (12.0 g/dL) 3
• Males: 134.9 g/L (13.5 g/dL) 3

Pregnancy-Specific Thresholds

• First trimester: 110.3 g/L (11.0 g/dL) 3
• Second trimester: 105.9 g/L (10.6 g/dL) 3

Critical Considerations for Elderly Patients

For patients over 70 years, the standard WHO criteria may overdiagnose anemia, as average hemoglobin levels naturally decline with age. 4

• In individuals over 70 years (men) and over 80 years (women), average hemoglobin levels fall below traditional WHO thresholds even in otherwise healthy individuals 4
• Some experts propose age-adjusted criteria: Hb <12 g/dL for both sexes in elderly populations 1
• Between 60-69 years, approximately 20% meet WHO criteria for anemia, increasing to 63% of females and 76% of males beyond age 90 4

Common pitfall: Applying standard adult thresholds to elderly patients may lead to unnecessary investigations and treatment in individuals with physiologically normal age-related hemoglobin decline. 4

Ethnicity Considerations

Current evidence does not support ancestry-specific hemoglobin thresholds. 3

• The 2024 international analysis found no evidence that thresholds should differ between people of different ancestries 3
• Previous suggestions of ethnicity-based variations were not supported by genetic studies examining variants affecting hemoglobin concentrations 3

Operational Classification Beyond Hemoglobin Level

Anemia diagnosis requires more than just hemoglobin measurement—the underlying mechanism and clinical context must be considered. 1

The operational approach includes:

• Severity grading: Mild (10-12 g/dL), moderate, or severe based on hemoglobin level 1
• Mechanism identification: Loss, destruction, or decreased production of red blood cells 5
• Morphological classification: Using additional hematologic parameters (MCV, RDW, reticulocyte count) 1
• Etiological classification: Nutritional deficiency (iron, folate, B12), chronic disease, or unexplained (particularly in elderly) 1