Bendamustine and Rituximab Treatment, Chronic Lymphocytic Leukemia, Direct Antiglobulin Test, and False Negatives

To the Editor,

We read “Early Direct Antiglobulin Test Negativity After Bendamustine and Rituximab Treatment in Chronic Lymphocytic Leukemia: Two Cases” [1]. Eren and Suyanı noted that “BR seems to be an important treatment of choice in terms of eliminating the poor prognostic factor of direct antiglobulin test (DAT) positivity and assuring safe cessation of steroid treatment due to rapid achievement of DAT negativity” [1]. The interesting observation of a negative DAT test should be discussed. There is another possibility that Eren and Suyanı did not mention. In their report, Eren and Suyanı noted that no titer was provided [1]. Whether the negative result is a false negative result should be discussed. For DAT testing, the prozone phenomenon is observable and it is important to consider this phenomenon in the interpretation of unexpected false negative DAT tests [2,3,4].

Dear Editor,

In their comments, Won Sriwijitalai and Viroj Wiwanitkit pointed out that the possibility of false negative direct antiglobulin test (DAT) was not denoted in our paper in which we shared our experience about the achievement of early DAT negativity in patients receiving bendamustine and rituximab treatment for chronic lymphocytic leukemia [1,2]. Along with the prozone phenomenon that the authors mentioned, there are other causes of a false negative DAT, including poor washing technique, improper agitation of specimen during reaction strength determination, failure to add or delayed addition of antihuman globulin reagent, inactive antihuman globulin reagent, inappropriately concentrated red blood cell suspension, and delay in testing [3]. However, we used an automated gel centrifugation method sytem to detect DAT which ensured quite accurate results. Also, the reported patients had normal hemoglobin, haptoglobulin, LDH, and indirect bilirubin levels during DAT negativity, suggesting that the existence of a high titer of antibody, the reason of prozone affect, was unfeasible. Additionally, sustained DAT negativity during follow-up led to the consideration that DAT negativity was accurate and false negative DAT was unlikely.

Best Regards,