Further Investigation of AHTR (Immune)

For an immune-mediated AHTR, the expected results are a misidentification error resulting in transfusion of ABO-incompatible RBC.

Clerical or Systems Error

If a clerical or systems error is found that indicates the patient has received a blood product that was not intended for the patient (such as an ABO-incompatible blood product):

• Immediately notify the
  • Patient's physician
  • transfusion service
  • MD responsible for the blood bank (or designate)
• Search records to determine if misidentification or incorrect issue of other blood components has put other patients at risk
• Document and report findings according to laboratory policies

Visible Hemolysis 

If visible hemolysis is present in the patient's post-transfusion blood sample:

• Compare with pre-transfusion blood specimen
• Investigate if the blood collection was a difficult draw that may have produced hemolysis and, if so, recollect
• Document and report findings according to laboratory policies

NOTE: The presence of methemalbumin can result in plasma having a brownish colour. When intravascular hemolysis occurs, methemalbumin is formed after the haptoglobin-binding capacity for free hemoglobin is exceeded and the free hemoglobin binds to albumin. If the post-transfusion specimen was drawn hours after the suspected reaction began, hemoglobin degradation products, such as bilirubin, may be in the bloodstream and cause icteric plasma (yellow discoloration).

Positive Direct Antiglobulin Test (DAT)

To be valid, a DAT should be performed on an EDTA specimen. An EDTA specimen will prevent complement from binding in vitro due to a harmless cold autoantibody such as autoanti-I, which many people have. If the DAT done on the patient's post-transfusion EDTA blood sample is positive:

• Perform a DAT on the pre-transfusion blood sample for comparison (unless already done). If the DAT on the pre-transfusion specimen is also positive, the positive DAT on the post-transfusion specimen is not suggestive of an immune-mediated hemolytic transfusion reaction.
• If the DAT on the pre-transfusion specimen is negative, a more complete investigation may be done, an example of which follows.

NOTE: The DAT on the patient's post-transfusion specimen may be negative -- even though a hemolytic transfusion reaction has occurred – if at the time of testing most or all transfused donor red cells have been removed by rapid intravascular hemolysis (IVH).

If none of the initial tests are positive, but evidence of hemolysis is present post-transfusion, suspect a non-immune cause such as transfusing a hemolysed unit or drug-blood incompatibilities.

Evidence of Hemolysis

Several laboratory tests performed outside the transfusion service in other sections of the clinical laboratory can confirm or suggest that hemolysis is occurring.

Test results most associated with IVH include hemoglobinemia, hemoglobinuria, and increased Lactate Dehydrogenase (LD) levels. Test results occurring with both IVH and EVH include unexplained decreased hemoglobin and hematocrit levels, decreased serum haptoglobin, and hyperbilirubinemia.

These laboratory tests can indicate that red cells are being destroyed but do not reveal why.

Additional Serologic Tests

If any of the initial observations and/or test results are positive, further investigation is warranted. Examples of follow-up tests that may be done include:

ABO and Rh(D) typing of patient's pre and post-transfusion specimens and implicated donor units.

Antibody screen on patient's pre and post-transfusion specimens and implicated donor units (if plasma is available).

NOTE: The antibody screen may be falsely negative if at the time of testing most of the patient's antibody has adsorbed to transfused donor cells. In such cases the DAT will be positive and the antibody can be identified in an eluate prepared from the patient's post-transfusion red cells.

Antibody identification. If a new or unexpected antibody is found in the antibody screen, it should be identified with subsequent antigen phenotyping of patient's pre-transfusion red cells and donor red cells (if available). If the antibody appeared post-transfusion, suspect a delayed hemolytic transfusion reaction due to an anamnestic antibody response following transfusion of antigen-positive red cells. If the patient was transfused with a product, such as Intravenous Immune Globulin (IVIG) or a large dose of Rh immune globulin (RhIG), e.g., to treat immune thrombocytopenia purpura, suspect passive antibodies.

Monospecific DATs. If the post-transfusion DAT is positive with polyspecific antiglobulin serum, the DAT can be repeated with monospecific anti-IgG and anti-C3b/-d to determine the substances sensitizing the patient's red cells. The major purpose is to assess if an elution should be performed to identify antibodies that may be sensitizing the patient's cells.

Elution. If IgG is sensitizing the patient's red cells, an eluate may be prepared from the DAT-positive red cells and tested with a panel to identify the antibodies involved.