Chapter 7: haemodilution, transfusion and donor testing
Updated 21 May 2024
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Large volume blood loss requiring intravenous fluid replacement therapy has the potential to lead to false negative screening test results owing to dilution of specific antibody or antigen below the lower limit of detection of the test.
The volume of fluid that may be infused before false negative results may occur depends on the size of the individual, amount of blood loss and the nature of the infused fluid, as well as the initial concentration of the analyte being tested for and the diagnostic test characteristics. A number of algorithms exist that allow for the estimation of haemodilution. Estimated haemodilution greater than 50% indicates that testing of pre-infusion samples should be undertaken for greater accuracy.
If the donor has been transfused with blood or blood products in the immediate pre-donation period (within 48 hours of donation) then the sample obtained prior to transfusion should be sought and tested. If a pre-transfusion sample is not available for testing, then this should be recorded and reported to clinicians responsible for transplantation.
Where a donor has received blood products or components in the preceding 3 months, the interpretation of serological results should take into account the possibility of the individual having acquired antibody passively from the blood product or component.
Consideration may be given to nucleic acid testing (NAT) where concern exists regarding haemodilution affecting serology-based tests, although the precise role of these tests is not yet known.