G6PD Activity Testing in RBCs
G6PD Activity Testing in RBCs
G6PD activity testing is crucial for diagnosing G6PD deficiency, the most common enzymatic disorder of red blood cells, affecting approximately 400 million people worldwide.
Key Points
- Essential enzyme in RBC metabolism
- X-linked inherited disorder
- Critical for oxidative stress protection
- Variable expression in females due to X-inactivation
Biochemical Basis
Enzyme Function
- Primary Role:
- Catalyzes first step of pentose phosphate pathway
- Generates NADPH for redox homeostasis
- Protects against oxidative stress
- Maintains RBC membrane integrity
- Molecular Characteristics:
- Gene location: Xq28
- Multiple variants identified (>400)
- Variable enzyme activity levels
- Age-dependent expression
Pathophysiology
- Reduced NADPH production
- Decreased glutathione regeneration
- Increased oxidative vulnerability
- RBC membrane damage and hemolysis
Testing Methods
Screening Tests
- Fluorescent Spot Test:
- Rapid qualitative assessment
- Based on NADPH fluorescence
- Suitable for mass screening
- Results within 10 minutes
- Methemoglobin Reduction Test:
- Visual colorimetric method
- Semi-quantitative results
- Less sensitive than other methods
Quantitative Methods
- Spectrophotometric Assay:
- Gold standard method
- Measures NADPH production rate
- Temperature-controlled conditions
- High precision and accuracy
- Cytochemical Assay:
- Individual cell analysis
- Useful for heterozygote detection
- Labor-intensive procedure
Clinical Applications
Indications for Testing
- Primary Screening:
- Neonatal screening programs
- Family history of G6PD deficiency
- High-risk ethnic groups
- Pre-medication screening
- Diagnostic Workup:
- Unexplained hemolysis
- Severe neonatal jaundice
- Drug-induced hemolysis
- Chronic non-spherocytic hemolytic anemia
Special Considerations
- Testing during acute hemolysis may be misleading
- Recent transfusion affects results
- Age-specific reference ranges needed
- Gender differences in manifestation
Result Interpretation
Reference Ranges
- Normal Values:
- Adults: 7-20.5 U/g Hb
- Newborns: 10-23 U/g Hb
- Variations by methodology and laboratory
Result Categories
- Class I (Severe):
- <10% of normal activity
- Chronic non-spherocytic hemolytic anemia
- Class II (Intermediate):
- 10-60% of normal activity
- Intermittent hemolysis
- Class III (Mild):
- 60-90% of normal activity
- Hemolysis with severe oxidant stress
Clinical Management
Preventive Measures
- Avoid triggering factors
- Medication review and adjustment
- Dietary recommendations
- Genetic counseling
Acute Management
- Hemolytic Crisis:
- Remove triggering factors
- Supportive care
- Transfusion if needed
- Monitor hemoglobin levels
- Neonatal Care:
- Close monitoring of bilirubin
- Phototherapy as needed
- Exchange transfusion protocols
- Follow-up planning
