What does an elevated Red Blood Cell (RBC) count mean?

Understanding Elevated Red Blood Cell Count

An elevated red blood cell (RBC) count typically indicates a condition called polycythemia, which can be either primary (due to bone marrow disorders) or secondary (due to physiological adaptations), and requires further evaluation to determine the underlying cause and appropriate management. 1

Causes of Elevated RBC Count

Elevated RBC counts can result from several underlying conditions:

Primary Causes (Bone Marrow Disorders)

• Polycythemia vera (a myeloproliferative neoplasm)
• Other myeloproliferative disorders

Secondary Causes (Physiological Adaptations)

• Chronic hypoxemia (low oxygen states)
• High altitude exposure 2
• Chronic lung disease
• Congenital heart disease
• Sleep apnea
• Smoking
• Dehydration (relative polycythemia)
• Inappropriate erythropoietin production (e.g., from kidney tumors)

Clinical Significance

An elevated RBC count has important clinical implications:

1. Increased blood viscosity: Higher RBC counts increase blood thickness, which can impair microcirculation and tissue perfusion

2. Thrombotic risk: Elevated RBC counts are associated with increased risk of venous and arterial thrombosis 3

3. Tissue hypoxia: Despite increased oxygen-carrying capacity, the increased viscosity may paradoxically reduce oxygen delivery to tissues

4. Cardiovascular strain: The heart must work harder to pump more viscous blood

Diagnostic Approach

When an elevated RBC count is identified, further evaluation should include:

• Complete blood count with differential to assess other cell lines
• Arterial blood gas analysis to evaluate oxygenation
• Erythropoietin levels
• JAK2 mutation testing (if polycythemia vera is suspected)
• Evaluation for hypoxic conditions (pulmonary function tests, sleep studies)
• Abdominal imaging to rule out renal or hepatic causes

Management Considerations

Management depends on the underlying cause:

• For secondary polycythemia: Treat the underlying condition (e.g., oxygen therapy for hypoxic conditions)
• For dehydration: Fluid rehydration
• For polycythemia vera: Therapeutic phlebotomy to maintain hematocrit <45% in men and <42% in women
• For severe cases: Consider cytoreductive therapy in consultation with hematology

Clinical Pitfalls and Caveats

• Don't assume all elevated RBC counts require intervention: Some elevations may be physiological adaptations (e.g., high altitude dwellers)
• Don't miss underlying malignancies: Elevated RBC count can be a paraneoplastic phenomenon
• Consider relative vs. absolute polycythemia: Dehydration can cause a relative increase in RBC concentration without true overproduction
• Monitor for thrombotic complications: Patients with elevated RBC counts are at higher risk for thrombosis 3
• Assess transfusion needs carefully: In patients requiring transfusion for other reasons, elevated baseline RBC counts may affect transfusion thresholds 1

Special Considerations in Trauma and Critical Care

In trauma and critical care settings, RBC transfusion decisions should be guided by:

• Hemodynamic stability rather than absolute RBC count 1
• Evidence of inadequate oxygen delivery
• Presence of active bleeding
• Underlying cardiovascular reserve

The AAGBI guidelines recommend maintaining hemoglobin above 70 g/L in most patients, with higher thresholds (80 g/L) for patients with ischemic heart disease 1.