Comparison of Polybrene DAT and Conventional DAT in Cases of Suspected DAT Negative Autoimmune Hemolytic Anemia (AIHA)

Introduction/Objective A negative Direct Antiglobulin Test (DAT) is seen in approximately 1-5% of patients presenting with signs and symptoms of immune hemolysis. A well-performed ‘standard’ DAT detects ~100-500 molecules of bound IgG per red cell. A more sensitive polybrene DAT may be helpful in order to confirm a diagnosis of AIHA in patients whose samples have tested negative via standard DAT. However, there has been little reported on utility of the polybrene DAT in evaluating such cases with modern DAT reagents. We hypothesized that the polybrene DAT would not contribute substantially to the analysis of Coombs-negative hemolytic anemia (C-NHA), based primarily on our anecdotal observation. As such, we undertook a study to assess results of polybrene DAT in cases evaluated for possible (C-NHA). Methods/Case Report Two study sites were used for data analysis (Yale-New Haven Hospital, Site A, and VA Connecticut, Site B) over a five year period (2016-2021). During this time, standard DATs were performed at both study sites by the tube method using polyspecific antiglobulin and, if positive, reflex to anti-IgG and -C3. For cases of suspected C-NHA (which are reported to Blood Bank via a consult mechanism), conventioned DAT- samples are referred to our regional immunohematology laboratory (American Red Cross, Farmington, CT) for manual hexadimethrine bromide (Polybrene) DAT. Polybrene DAT is reported as negative with two sources of polyspecific AHG. Subsets of patients also underwent acid elution studies (Gamma ELU-KITII) as part of a C-NHA algorithm developed during the study period. Results of standard DAT, acId elution, and polybrene DAT were extracted from Blood Bank electronic records at both study sites. Results (if a Case Study enter NA) Evaluation for C-NHA was performed in 32 patients/cases over the study period. Amongst these individuals, 96.8% (31/32) underwent polybrene DAT assessment and none (0%; 0/31) demonstrated a positive polybrene DAT result. Notably, acid elution studies were performed in 90.6% (29/32) of traditional DAT negative cases. Of these, 10.3% (3/29) had reactive eluates. Conclusion Performance of the polybrene DAT appeared to be of no value in the assessment of suspected C-NHA. Given that nearly 10% of individuals with a negative conventional DAT had a positive acid elution, this testing step appears to be of greater value in potentially identifying an autoantibody in suspected cases of C-NHA.