Plasma Erythropoietin (EPO) Levels
Introduction
- Glycoprotein hormone crucial for erythropoiesis
- Primary regulator of red blood cell production
- Produced mainly by peritubular interstitial cells of the kidney
- Small amounts produced by hepatocytes
Basic Characteristics
- Molecular weight: 30.4 kDa
- Half-life: 2-13 hours
- Primary stimulus: Tissue hypoxia
- Major target: Erythroid progenitor cells
Physiology & Regulation
Production Mechanism
- Oxygen-dependent regulation
- HIF-1α pathway activation
- Increased transcription under hypoxic conditions
- Negative feedback through increased RBC mass
- Non-oxygen dependent factors
- Iron status
- Inflammatory cytokines
- Hormonal influences
Biological Actions
- Promotion of erythroid progenitor survival
- Stimulation of erythroid differentiation
- Prevention of apoptosis in erythroid precursors
- Enhancement of iron uptake and utilization
- Non-erythropoietic effects:
- Tissue protection
- Angiogenesis
- Wound healing
Clinical Applications
Indications for Testing
- Primary Indications:
- Unexplained anemia
- Polycythemia evaluation
- Chronic kidney disease
- Suspected EPO-producing tumors
- Secondary Indications:
- Response monitoring to anemia treatment
- Assessment of bone marrow failure
- Investigation of congenital erythrocytosis
- Evaluation of EPO resistance
Specimen Requirements
- Sample type: Serum or EDTA plasma
- Collection timing: Morning preferred
- Processing: Separate and freeze within 4 hours
- Storage: -20°C for extended periods
Interpretation & Analysis
Reference Ranges
- Neonates: 15-100 mU/mL
- Infants (1-6 months): 11-45 mU/mL
- Children: 5-34 mU/mL
- Adolescents: 4-27 mU/mL
Clinical Correlation
- Appropriate EPO Response:
- Inversely proportional to hemoglobin level
- Exponential increase with decreasing hematocrit
- Normal response: Log(EPO) = 4.7 - (0.13 × Hct)
- Inappropriate Response:
- High EPO with normal/high Hct: EPO-producing tumors
- Low EPO with anemia: CKD, inflammatory conditions
- Normal EPO with severe anemia: Relative EPO deficiency
Special Considerations
Disease-Specific Patterns
- Chronic Kidney Disease:
- Reduced EPO production
- Target range: 10-30 times normal
- Monitoring for EPO resistance
- Thalassemia:
- Inappropriately low EPO levels
- Correlation with transfusion dependency
- Impact on chelation therapy
- Diamond-Blackfan Anemia:
- Elevated EPO levels
- Poor response to EPO therapy
- Diagnostic significance
Therapeutic Implications
- EPO Replacement Therapy:
- Starting dose calculation
- Response monitoring
- Resistance evaluation
- Monitoring Parameters:
- Hemoglobin response
- Iron status
- Blood pressure
- Adverse effects
Further Reading
