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Dilutions and dilution factors
Parts, volumes, serial steps, and the reported result
Adding diluent lowers concentration. The dilution factor (DF) is the final volume divided by the specimen volume. A DF of 5 gives one fifth of the original concentration.1
Example: 1:5 dilution
Here, 1:5 means one specimen part in five final parts. Mix one specimen part with four diluent parts. A written 1 + 5 means one specimen part plus five diluent parts, which gives a DF of 6.1
Specimen
100 µL
Diluent
100 µL
Diluent
100 µL
Diluent
100 µL
Diluent
100 µL
Equal-volume schematic. µL = microliter.
Calculating the dilution factor
DF = final volume ÷ specimen volume
Final volume = 500 µL
Specimen volume = 100 µL
DF = 500 ÷ 100 = 5
Volumes and factor
- Specimen volume
Final volume ÷ DF - Diluent volume
Final − specimen volume
Prepare a 1:10 dilution with a final volume of 1.0 mL.
Specimen = 1.0 ÷ 10 = 0.10 mL.
Diluent = 1.0 − 0.10 = 0.90 mL.
mL = milliliter. 1 mL = 1,000 µL.
Concentration and result
- Diluted concentration
Original concentration ÷ DF - Original concentration
Diluted concentration × DF
A 1:5 aliquot measures 84 U/L.
84 × 5 = 420 U/L in the original specimen. U/L = units per liter.
Apply the factor only once. Report an analyzer-corrected result of 420 U/L as 420 U/L. Use the method's diluent and validated measuring range.2
Cumulative dilution factor
Original specimen
1:5 step
Total DF = 5
1:4 step from that mixture
Total DF = 5 × 4 = 20
Each step dilutes the well-mixed solution from the preceding tube, so the cumulative dilution factor is the product of the step factors. A result of 12 mg/dL in the second tube gives 12 × 20 = 240 mg/dL in the original specimen. mg/dL = milligrams per deciliter.1