How does the World Health Organization (WHO) classify anemia severity in adult men, non-pregnant women, and pregnant women based on hemoglobin levels?

WHO Classification of Anemia Severity

The World Health Organization defines anemia as hemoglobin <13.0 g/dL in adult men, <12.0 g/dL in non-pregnant women, and <11.0 g/dL in pregnant women. 1

Diagnostic Thresholds by Population

Adult Men

• Anemia is defined as hemoglobin <13.0 g/dL 2, 1

Non-Pregnant Women (≥15 years)

• Anemia is defined as hemoglobin <12.0 g/dL 2, 1

Pregnant Women

• Anemia is defined as hemoglobin <11.0 g/dL 2, 1

Severity Classification for Women

The WHO establishes specific severity categories for women aged ≥15 years based on hemoglobin concentrations: 1

• Mild anemia: 11.0-11.9 g/dL 1
• Moderate anemia: 8.0-10.9 g/dL 1
• Severe anemia: <8.0 g/dL 1

Clinical Thresholds for Investigation

Men with hemoglobin <12 g/dL and postmenopausal women with hemoglobin <10 g/dL should be investigated more urgently, as lower hemoglobin levels suggest more serious underlying disease. 2

The lower limit of the normal range for the laboratory performing the test is reasonable to define anemia, as normal hemoglobin distribution varies between different populations. 2

Important Clinical Caveats

• These WHO thresholds were established in 1968 based on predominantly Caucasian populations in Europe and North America, and normal hemoglobin distribution varies with sex, ethnicity, and physiological status 1, 3
• Even mild anemia according to WHO criteria is associated with increased perioperative morbidity and mortality, respiratory complications, septic complications, thromboembolic events, myocardial injury, and cognitive decline in elderly individuals 1
• Any level of anemia should be investigated in the presence of iron deficiency markers 2