Sickle Cell Solubility Test
Sickle Cell Solubility Test
Key Points
- Rapid screening test for hemoglobin S
- Based on reduced solubility of HbS in high molarity phosphate buffer
- Results available within 5-10 minutes
- Suitable for emergency screening
Introduction
The Sickle Cell Solubility Test (SCST), also known as Sickling Test or Solubility Test, is a rapid diagnostic screening method for detecting the presence of hemoglobin S (HbS). This test exploits the unique property of HbS to form tactoids in deoxygenated, concentrated phosphate buffer solutions.
Testing Procedure
Required Materials
- 2.3M phosphate buffer solution
- Sodium dithionite (reducing agent)
- Test tubes
- Whole blood sample
- Positive and negative controls
Step-by-Step Procedure
- Sample Preparation:
- Collect 2ml fresh whole blood in EDTA tube
- Centrifuge if needed (for packed cells)
- Maintain sample at room temperature
- Reagent Preparation:
- Add sodium dithionite to phosphate buffer
- Mix until completely dissolved
- Prepare fresh for each batch
- Testing Steps:
- Add 2ml buffer solution to test tube
- Add 50μL of patient blood
- Mix gently but thoroughly
- Incubate at room temperature for 5 minutes
- Place tube against lined paper or text
Quality Control Measures
- Run positive and negative controls with each batch
- Check reagent expiration dates
- Monitor room temperature (20-25°C)
- Verify buffer concentration
Result Analysis
Visual Assessment
- Positive Result:
- Turbid or cloudy appearance
- Lines behind tube not visible
- Indicates presence of HbS
- Negative Result:
- Clear solution
- Lines behind tube clearly visible
- No HbS present
Critical Considerations
- False Positives:
- High protein concentrations
- Multiple myeloma
- Severe hyperglobulinemia
- False Negatives:
- Severe anemia (Hb <7 g/dL)
- Recent transfusion
- Neonates (high HbF)
Clinical Applications
Primary Indications
- Emergency screening before surgery
- Rapid assessment in acute pain crisis
- Initial screening in outpatient settings
- Population screening programs
Advantages
- Rapid results (5-10 minutes)
- Cost-effective
- Minimal equipment needed
- Simple to perform
- High sensitivity for HbS
Limitations and Precautions
- Test Limitations:
- Cannot differentiate trait from disease
- Not reliable in infants <6 months
- Cannot detect other hemoglobinopathies
- Requires confirmation by electrophoresis
- Safety Precautions:
- Use fresh reagents
- Proper sample handling
- Universal precautions for blood samples
- Proper disposal of materials
Follow-up Testing
- Hemoglobin electrophoresis
- High-performance liquid chromatography (HPLC)
- Genetic testing when indicated
- Family screening recommendations
