Laboratory Procedure for 1/10 Dilution of Serum Sample for CK Assay
To make a 1/10 dilution of a serum sample with saline for CK assay, use 0.05 mL of sample and 0.45 mL of saline diluent. 1
Rationale and Procedure
The dilution ratio of 1/10 means that the sample represents 1 part out of a total of 10 parts in the final solution. Since the analyzer requires a minimum volume of 0.5 mL, the calculation is:
- Sample volume: 0.05 mL (1 part)
- Diluent volume: 0.45 mL (9 parts)
- Total volume: 0.5 mL (10 parts)
This ensures that the sample is properly diluted while meeting the minimum volume requirement of the analyzer.
Step-by-Step Protocol
- Obtain a clean test tube or appropriate container
- Using a calibrated pipette, add 0.05 mL (50 μL) of the serum sample
- Add 0.45 mL (450 μL) of sterile 0.9% saline using a calibrated pipette
- Mix thoroughly but gently to ensure homogeneity without causing hemolysis
- Process the diluted sample according to standard laboratory procedures
- When reporting results, multiply the measured value by 10 to account for the dilution factor
Important Considerations
- Use calibrated pipettes to ensure precise measurement of both sample and diluent volumes
- Ensure proper mixing to achieve a homogeneous solution
- Document the dilution factor (1:10) for proper result interpretation
- Avoid using saline-filled needles for initial sample collection as this would pre-dilute the sample
- Use only sterile 0.9% saline as the diluent, as recommended by standard laboratory practices
Common Pitfalls to Avoid
- Inadequate mixing leading to non-uniform distribution of the analyte
- Calculation errors when applying the dilution factor to the final result
- Using inappropriate diluent other than normal saline
- Failing to document the dilution factor for proper result interpretation
Following this standardized procedure ensures accurate quantification of high CK levels that are outside the instrument's measurement range.