Contributed by Lara Berklite, MDFINAL DIAGNOSIS
Most likely drug-induced hemolytic anemia due to bendamustine.
DISCUSSION
Overall, the patient's clinical symptoms, pink plasma, low haptoglobin, elevated LDH, and elevated plasma free hemoglobin were consistent with an acute hemolytic process. The differential diagnosis included non-immune causes and immune causes. Non-immune causes such as heat induced hemolysis by the blood warmer, incompatible solutions, dysfunctional or inappropriate gauge of the infusion needle/catheter were excluded. An extensive laboratory work up with enhanced indirect Coombs techniques, with "super" Coombs, flow cytometry studies, eluate and multiple crossmatches didn't yield a positive result. Drug study by immune-complex mechanism was also negative. Study for PNH was negative. The red cell membrane sequencing is still pending. Although drug induced hemolytic anemia to Bendamustine is a possibility, a temporal association of the hemolytic episode with the transfusion is somewhat hard to explain by bendamustine-related process alone. G6PD study of the patient and the donor could be considered.
Bendamustine is an alkylating drug indicated for the treatment of indolent B-cell non-Hodgkin's lymphoma (NHL) that has progressed despite treatment with rituximab as well as chronic lymphocytic leukemia (CLL) [1]. Bendamustine acts via electrophilic alkyl groups to crosslink DNA, but also contains a purine-like benzimidazole that makes it similar in structure to fludarabine [1]. Fludarabine is known to cause severe hemolytic anemia [2-4]. There have been case reports of hemolytic anemia in patients who received bendamustine [5-7]. Glance et al reported a case of a 64 year old female with stage III follicular lymphoma who had hemolytic anemia one month after her 4th cycle of bendamustine [6]. Goldschmidt et al reported five cases of hemolytic in CLL patients treated with bendamustine, two of which were DAT negative like our case [5].
Drug-induced hemolytic anemia can be a result of drug-induced antibodies or nonimmunologic protein adsorption (NIPA) [8-9] (Table 21-18). NIPA occurs when a drug induces RBC membrane changes that causes plasma proteins to be adsorbed onto the RBCs resulting in a positive DAT. Drug-induced antibodies can be further subdivided into drug-dependent antibodies and drug-independent antibodies. Drug-independent antibodies are serologically indistinguishable from other warm IgG antibodies. Drug-dependent antibodies on the other hand will react with drug-treated RBCs, untreated RBCs in the presence of a solution of the drug or both [8]. There are several different theories of how drug-dependent antibodies function. One is that drug-antibody immune complexes form in circulation and are adsorbed onto RBC membranes and subsequently activate complement resulting in hemolysis [10]. Alternatively, an antibody may form to a combination of drug and RBC membrane antigens or to a neoantigen that is created as a result of drug exposure [10]. Two different testing methods can be used to detect drug-dependent antibodies, the drug solution addition method or immune complexing mechanism and the drug adsorption method.
The drug solution addition method or immune-complexing mechanism tests the patient's serum against RBCs in the presence of a solution drug. The sensitivity of this testing method can be enhanced by adding a source of complement such as normal sera. The results needed to determine that a drug-induced antibody is present by this testing method are illustrated in Table 21-19 [9]. If complement plus drug without patient serum is positive, NIPA may be present. In the drug adsorption method the patient's serum as well as the eluate from the patient's RBCs are tested for agglutination or hemolysis against drug-treated cells. Necessary testing results to determine that a drug-induced antibody is present by this method is illustrated in Table 21-20 [9]. If normal sera reacts with drug-treated but not un-treated RBCs, this may be explained by nonimmunologic protein adsorption (NIPA). To confirm NIPA, dilutions of patient's serum can be tested. The diluted sera will not react with the cells if NIPA is present. Alternatively, with this pattern of results a low-titer antibody to drug may be present in the normal sera as a result of environmental exposure.
In our case, the reason for the patient's acute hemolytic reaction is still not completely clear. Our work up ruled out non-immune causes as well as RBC alloantibodies as a cause of immune mediated hemolysis. Bendamustine remains a potential culprit, although testing by the drug solution addition method for the most common immune-complex mechanism and DAT were negative. As mentioned above, in the case reports of bendamustine associated hemolysis DAT can be negative. Unfortunately, in those cases no drug studies were performed to confirm the presence of drug-induced antibodies. Although initial testing for drug-induced antibodies results in our case was negative, a drug-induced antibody may still be detected via the drug adsorption method. Additionally, there are other modifications that can reveal a drug-induced antibody even when both testing methods fail. These include testing with a different concentration of drug, washing prior to the antiglobulin test with drug solution, and testing drug metabolites [8]. Our patient was taken off bendamustine given concerns for another hemolytic reaction. Unfortunately, in some clinical situations when laboratory testing is negative, the only way to determine if hemolysis is caused by a drug, especially when it is the treatment of choice, is to put the patient back on the treatment and observe the patient closely for hemolysis.
REFERENCES
Contributed by Lara Berklite, MD
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