Question

A 42 year old woman was introduced to the Emergency Room with complaints of abdominal pain for the past few days. She was also reported her stools have been black and sticky. She suspected to have GI (gastro-intestinal) bleeding. According to her medical history, she was transfused with 2 units washed packed RBCs 6 months ago for the same symptoms. The CBC results were:

WBCs: 5.7 X 10³/µl

RBCs: 2.95 X 10⁶/µl

HGB: 6.3g/dL

Hematocrit: 19.8%

According to her anemic condition, she was admitted to the hospital for treatment and given 3 units of packed RBCs (each blood unit should increase hemoglobin level by 1g/dL, but she was given 3 units since she had an active GI bleeding). She is type B positive with a negative antibody screening {1} which means no antibodies were observed in her plasma. The 3 units were cross-matched and transfused without adverse reactions. One day later, she was discharged. Two days after discharge, she returned to the Emergency Room with yellowish eyes and skin (jaundice). The CBC at this time showed HGB = 5.8g/dL and elevated bilirubin level indicated hemolysis of RBCs. She was ordered with 2 units of packed red blood cells. At this time, the antibody screen was now positive {2}. Anti-JK^b was found in her plasma and positive DAT was observed.

She was diagnosed with a delayed hemolytic transfusion reaction (DHTR) due to anti-JK^b

1.       Discuss this condition DHTR?

2.       Why the first antibody screening {1} was negative? (Knowing that anti-JK^b was present in her plasma from exposure of JK^b positive blood via previous blood transfusion according to her medical history)? However, it is really negative since no immediate HTR was observed

3.       Why the second antibody screening{2} becomes positive after blood transfusion?

4.       If DAT was performed by gel-method, and positive mixed field result was observed. What does this mean?

Answer 1

1.Delayed hemolytic transfusion reactions (DHTRs) occur in patients who have received transfusions in the past. These patients have very low antibody titers that are undetectable on pretransfusion testing, so that seemingly compatible units of red blood cells (RBCs) are transfused.

2. Why the first antibody screening {1} was negative? (Knowing that anti-JKb was present in her plasma from exposure of JKb positive blood via previous blood transfusion according to her medical history)? However, it is really negative since no immediate HTR was observed

These reactions occur in patients who have been alloimmunized to minor RBC antigens during previous transfusions or pregnancies; pretransfusion testing fails to detect these alloantibodies due to their low titer

3. Why the second antibody screening{2} becomes positive after blood transfusion?

After reexposure to antigen-positive RBCs, an antibody response occurs, with a rapid rise in antibody titer. Decreased survival of the transfused RBCs may result, primarily due to extravascular hemolysis. In the majority of cases, however, antibody production does not cause detectable hemolysis. The term delayed serologic transfusion reaction (DSTR) defines reactions in which an anamnestic antibody is identified serologically, in the absence of clinical evidence of accelerated RBC destruction. Antigens implicated most often in DHTRs are in the Kidd, Duffy, Kell, and MNS systems, in order of decreasing frequency.

4. If DAT was performed by gel-method, and positive mixed field result was observed. What does this mean?

A positive DAT means that there are antibodies attached to the RBCs. In general, the stronger the DAT reaction (the more positive the test), the greater the amount of antibody bound to the RBCs, but this does not always equate to the severity of symptoms, especially if the RBCs have already been destroyed.