Diagnostic Hemoglobin Thresholds for Anemia
Anemia is diagnosed when hemoglobin falls below 130 g/L in adult men and below 120 g/L in non-pregnant adult women, with pregnant women in the second and third trimester diagnosed at <110 g/L. 1
Standard Diagnostic Thresholds
The World Health Organization criteria, endorsed by the British Society of Gastroenterology (2021), establish the following hemoglobin cutoffs for anemia diagnosis:
- Adult men (>15 years): <130 g/L 1
- Non-pregnant adult women (>15 years): <120 g/L 1
- Pregnant women (2nd and 3rd trimester): <110 g/L 1
Important Clinical Considerations
Laboratory-Specific Reference Ranges
While WHO thresholds provide standardized criteria, anemia should be defined as hemoglobin below the lower limit of normal for your specific laboratory performing the test, provided these align with WHO-defined lower limits. 1 This accounts for population-specific variations in normal hemoglobin ranges. 1
Alternative Thresholds in Specific Guidelines
Some guidelines use slightly different cutoffs:
- The American Society of Hematology and chronic kidney disease guidelines define anemia as hemoglobin <135 g/L in adult males and <120 g/L in adult females 1, 2, 3
- Older British Society of Gastroenterology guidelines (2000) used variable thresholds (Hb <125-138 g/dL for men, <100-115 g/dL for women) 1
The 2021 BSG guidelines with WHO thresholds (130/120 g/L) represent the most current, consensus-based standard and should be used in clinical practice. 1
Critical Pitfalls to Avoid
Investigation Threshold vs. Diagnostic Threshold
Any level of anemia warrants investigation when iron deficiency is present, not just severe anemia. 1 The NICE fast-track referral thresholds for suspected GI malignancy (<110 g/L in men, <100 g/L in non-menstruating women) will miss cases of colorectal cancer, particularly in men. 1
Populations Requiring Modified Interpretation
Standard definitions may not apply to:
- Elderly individuals (≥70 years) 2, 3
- Pregnant or menstruating women 2
- Smokers 2
- Those at high altitude 2, 3
- Non-Caucasian populations 2
- Patients with chronic lung disease or hemoglobinopathy 2
Plasma Volume Expansion Masquerading as Anemia
In heart failure and chronic liver disease, low hemoglobin concentration may reflect expanded plasma volume rather than reduced total hemoglobin mass. 4 This represents true anemia requiring different management than hemoglobin deficiency. 4
Age-Related Considerations
Do not adjust hemoglobin thresholds downward for age in males, despite lower mean values in men >60 years. 1 Concurrent pathological conditions frequently explain lower hemoglobin in older males, and assuming age-related decline is normal may miss treatable disease. 1