Appendix 2: Calculation of blood and plasma dilution

The following algorithm is used for determining the suitability of post-transfusion/infusion samples for mandatory screening for transmissible infections. It is based on the algorithm developed by the Food and Drug Administration (FDA).

Step 1: Determine which sample is suitable for testing

Figure 1: Decision process

Use this flow chart to determine whether a blood sample or a pre-transfusion/infusion sample should be tested, or whether the algorithm (Step 2) should be applied.

A flow chart showing the process to determine the suitability of post-transfusion or post-infusion samples for mandatory screening for transmissible infections. A description of the process is provided below the diagram. Following the flow chart is the procedure for applying the suitability algorithm.

Description of Figure 1: Decision process
  1. Has the donor been transfused?
    1. If No, test a blood sample.
    2. If Yes, continue to number 2.
  2. Is the donor an adult (12 years old or above)?
    1. If No, continue to number 3.
    2. If Yes, continue to number 4.
  3. Is there a recent pre-transfusion or pre-infusion sample available?
    1. If No, apply the algorithm for assessing dilution. See Step 2 on the page below.
    2. If Yes, test the pre-transfusion or pre-infusion sample.
  4. Is there a recent pre-transfusion or pre-infusion sample available?
    1. If No, continue to number 5.
    2. If Yes, test the pre-transfusion or pre-infusion sample.
  5. Has blood loss occurred?
    1. If No, test a blood sample.
    2. If Yes, continue to number 6.
  6. Has the donor received 2000 mL of blood or colloids within 48 hours, or received 2000 mL of crystalloids within 1 hour, or received 2000 mL of a combination of blood, colloids and crystalloids?
    1. If No, test a blood sample.
    2. If Yes, apply the algorithm for assessing dilution. See Step 2 on the page below.

Step 2: Algorithm to assess dilution

Step 2a: Calculate volumes

1. Calculate donor plasma volume

Donor weight (kg) ÷ 0.025 = donor plasma volume (mL)

2. Calculate donor blood volume

Donor weight (kg) ÷ 0.015 = donor blood volume (mL)

3. Record volume of blood transfused

(in the 48 hours prior to death or sample collection, whichever comes first)

Add the following to calculate the volume of blood transfused (mL):

  • Red blood cells in 48 hours (mL)
  • Whole blood in 48 hours (mL)
  • Reconstituted blood in 48 hours (mL)

The volume of blood transfused (mL) is Sum A.

4. Record volume of colloid infused

(in the 48 hours prior to death or sample collection, whichever comes first)

Add the following to calculate the volume of colloids transfused (mL):

  • Plasma in 48 hours (mL)
  • Platelets in 48 hours (mL)
  • Albumin in 48 hours (mL)
  • Hydroxyethyl starch (HES) or other colloids in 48 hours (mL)

The volume of colloids transfused (mL) is Sum B.

5. Record volume of crystalloid infused

(in the 1 hour prior to death or sample collection, whichever comes first)

The volume of crystalloid infused (mL) is Sum C.

Step 2b: Assess dilution

1. Calculate volume of plasma transfused

Sum B + Sum C = volume of plasma transfused (mL)

2. Calculate total volume transfused

Sum A + Sum B + Sum C = total volume transfused (mL)

3. Calculate plasma dilution

Is the volume of plasma transfused greater than the donor plasma volume?

  • Yes
  • No

4. Calculate blood dilution

Is the total volume transfused greater than donor blood volume?

  • Yes
  • No

5. Determine sample suitability

If the answers to both questions above are 'No', the post-transfusion/infusion sample is acceptable.

If the answer to either question above is 'Yes', use a pre-transfusion/infusion sample. If a suitable sample is not available, seek expert advice and inform transplant centre, testing laboratory, tissue bank as necessary.

Last updated in TD-DSG Edition 203 Release 32 (26 July 2018)