Calculating Serum Dilution
When 0.5 mL of serum is added to 1.5 mL of saline, the serum dilution is 1:4.
Understanding Dilution Calculations
When calculating dilution factors in laboratory settings, we need to consider the total volume and the volume of the original sample. The dilution is expressed as a ratio of the original sample to the total volume.
Step-by-Step Calculation:
- Volume of serum = 0.5 mL
- Volume of saline = 1.5 mL
- Total volume = 0.5 mL + 1.5 mL = 2.0 mL
The dilution factor is calculated as:
- Total volume ÷ Volume of serum = 2.0 mL ÷ 0.5 mL = 4
Therefore, the serum dilution is 1:4 (one part serum to four parts total volume).
Verification Using Laboratory Standards
This calculation method is consistent with standard laboratory practices for preparing dilutions as outlined in clinical microbiology guidelines 1. When preparing dilutions, the ratio represents how many times more dilute the final solution is compared to the original sample.
Clinical Relevance of Proper Dilution Calculations
Accurate dilution calculations are critical in laboratory medicine for:
- Antimicrobial susceptibility testing where precise concentrations are needed 1
- Preparation of potassium solutions where exact dilutions affect patient safety 2
- Intralesional injections where dilution factors can minimize medication side effects 3
Common Pitfalls in Dilution Calculations
Confusing dilution ratio with dilution factor: The dilution ratio (1:4) indicates one part serum to three parts diluent, while the dilution factor (4) indicates how many times more dilute the solution is.
Ignoring the original sample volume in total volume: Always remember that the total volume includes both the sample and the diluent.
Misinterpreting the ratio: A 1:4 dilution means the original sample is diluted 4-fold, not that 1 part is mixed with 4 parts diluent.
Alternative Expression Methods
The same dilution can be expressed in different ways:
- As a fraction: 1/4 or 0.25
- As a percentage: 25% (of the original concentration)
- As parts: 1 part serum to 3 parts saline
Understanding these different expressions is important when following laboratory protocols that may use varying terminology.