Question

An 18-year-old man was admitted with multiple injuries after he and a passenger, another 18-year-old man, were in a motor vehicle accident. After receiving 50 mL of the first unit of blood, the patient developed shaking chills and became hypotensive. The unit of blood was immediately discontinued and the blood bank was asked to recheck the crossmatch STAT.

Laboratory Testing:

Clerical Check                          No evidence of blood bank clerical errors.

Hemoglobinemia                      Slight hemolysis observed

Pre-transfusion DAT                 Negative

Post-transfusion DAT               Weakly positive (mixed field)

Recheck of blood grouping

Recheck of Crossmatching       Patient pre-transfusion specimen and donor segment = compatible (IS)

                                               Patient post-transfusion specimen and donor segment = incompatible (IS)

Interpretation

What info do you gather from the test results and info given?

Answer 1

Hemolysis in the post-transfusion sample, but not the pre-transfusion sample is suspicious of a hemolytic transfusion reaction. As little as 20 mg/dL of hemoglobin will make the plasma appear pink, while 50 mg/dL or more will make it appear red. This degree of hemoglobinemia corresponds to the hemolysis of 4 to 10 mL of RBCs. Hemolysis in both samples suggests that some other explanation must be sought.If the DAT is positive on the post-reaction specimen, a pre-transfusion reaction sample should be tested for comparison. If the post transfusion DAT is positive, but the pre-transfusion DAT is negative a hemolytic transfusion reaction is possible. Since circulating antibody or complement coated red cells may be rapidly cleared, the DAT may be negative especially if the specimen was drawn several hours after the suspected reaction. If incompatible transfused cells have been partially destroyed, the DAT may have a mixed field appearance. The DAT will be positive if at least 10% of a patient’s red cells are coated with IgG.

Pre and post crossmatches should be performed, including the antiglobulin phase, to detect an antibody to a low frequency antigen or an error in pretransfusion testing. Whenever possible, the pre-transfusion crossmatch should be repeated with cells from a retained segment. If an incompatibility is found, a second crossmatch should be performed with the pre-transfusion serum and donor unit red cells to see if incompatibility was present prior to transfusion.

1. If both pre and post-reaction crossmatches are incompatible, an error was almost certainly made during pre-transfusion testing. The donor specimen used for the original crossmatch may have been taken from a different unit or the patient’s antibody screen was incorrectly read as negative.
2. If the crossmatch is incompatible with the post-reaction specimen but compatible with the pre-reaction specimen, anamnestic recall of antibody may have occurred. Antibody may have developed to red cells transfused in the preceding few days. Less likely, antibody may have been present in the transfused blood component and passively transfused.

Once an antibody has been identified, it is helpful to antigen type red cells from the transfused units to determine how many units were incompatible. The potential severity of hemolysis can be estimated from the number of antigen positive units transfused.

Acute hemolytic transfusion reaction

An acute hemolytic transfusion reaction (AHTR), also called immediate hemolytic transfusion reaction, is a life-threatening reaction to receiving a blood transfusion. AHTRs occur within 24 hours of the transfusion and can be triggered by a few milliliters of blood. The reaction is triggered by pre-formed host antibodies destroying donor red blood cells. AHTR typically occurs when there is an ABO blood group incompatibility, and is most severe when type A donor blood is given to a type O recipient

Signs and symptoms

Early acute hemolytic transfusion reactions are typically characterized by fever, which may be accompanied by rigors (chills). Mild cases are also typically characterized by abdominal, back, flank, or chest pain. More severe cases may be characterized by shortness of breath, low blood pressure, hemoglobinuria, and may progress to shock and disseminated intravascular coagulation. In anesthetized or unconscious patients, hematuria (blood in the urine) may be the first sign of AHTR. Other symptoms include nausea, vomiting, and wheezing.

Causes

The most common cause of acute hemolytic transfusion reaction is ABO incompatibility, which is typically due to human error that results in a recipient receiving the incorrect blood product. Rarely, other blood type incompatibilities can cause AHTR, the most common of which is Kidd antigen incompatibility. Rh, Kell, and Duffy antigen incompatibility have also been implicated in AHTR.