What is considered an elevated red blood cell (RBC) count in adults?

Elevated Red Blood Cell Count: Diagnostic Thresholds

An elevated red blood cell count (erythrocytosis) is defined as a hemoglobin level above 16.5 g/dL in adult males or above 16.0 g/dL in adult females, or when the red cell mass exceeds 125% of the predicted value for sex and body mass. 1, 2

Sex-Specific Diagnostic Thresholds

Males

• Hemoglobin >16.5 g/dL indicates erythrocytosis and warrants investigation 1, 3
• Normal hemoglobin range: 13.5-16.5 g/dL 4, 3
• Red cell mass >125% of predicted value confirms absolute erythrocytosis 1, 2

Females

• Hemoglobin >16.0 g/dL indicates erythrocytosis 3
• Normal ranges differ significantly from males for all erythrocyte parameters 3
• Sex-specific thresholds are essential because haematological indices vary substantially between men and women 3

Clinical Context Modifiers

The standard thresholds may require adjustment in specific populations 4:

• High altitude residents - physiologic erythrocytosis occurs as an adaptive response, though excessive elevation can lead to chronic mountain sickness 5
• Active smokers - may have elevated baseline hemoglobin 4
• Chronic lung disease patients - secondary erythrocytosis from chronic hypoxemia 4
• Age ≥70 years - though mean hemoglobin decreases with age in males, lower levels often indicate pathological conditions rather than normal aging 4

Initial Diagnostic Approach

When erythrocytosis is suspected based on elevated hemoglobin:

1. Confirm with repeat testing - verify the elevated hemoglobin is persistent, not transient 2

2. Measure erythropoietin (EPO) level - this is the critical first step in determining etiology 1, 2:

   • Low EPO → indicates primary erythrocytosis (e.g., polycythemia vera with JAK2 mutation) 6, 1
   • Normal or elevated EPO → indicates secondary erythrocytosis from hypoxemia, EPO-secreting tumors, or congenital causes 6, 1

3. Consider patient age and family history 1:

   • Young patients with family history → suspect congenital causes (familial erythrocytosis types 1-8) 6
   • Older patients without family history → more likely acquired causes 1

Common Pitfalls to Avoid

• Do not ignore sex-specific reference ranges - using male thresholds for females or vice versa will lead to missed diagnoses or false positives 3
• Do not assume elevated hemoglobin always represents pathology in high-altitude residents - modest erythrocytosis is adaptive, though excessive elevation (chronic mountain sickness) requires intervention 5
• Do not skip EPO measurement - this single test efficiently directs the entire subsequent workup toward primary versus secondary causes 1, 2
• Do not attribute low hemoglobin to normal aging in elderly males - values below 13.5 g/dL warrant investigation even in older men 4