(P-TS-103) The Utility Of An Acid Elution When A Direct Antiglobulin Test Is Positive Due To Complement Alone.

The intent of an acid elution is to recover immunoglobulin G (IgG) antibodies from the red blood cell (RBC) surface of a recently transfused patient. Most eluates prepared from samples direct antiglobulin test (DAT) positive for complement (C3) alone are expected to be nonreactive. However, it is possible to obtain clinically significant results from acid elution studies performed on these RBCs. This study examines how often clinically relevant information is obtained when an acid elution is performed on a sample that is positive for C3 DAT alone. In addition, this study intends to develop guidelines directing the performance of an acid elution on C3 DAT positive samples to reduce elution performance when clinically relevant information is unlikely to be obtained.

Study

Design/Methods:

An 11.5-month retrospective data analysis was performed on results obtained from a blood center’s immunohematology reference laboratories (IRLs). All patient samples with a negative IgG DAT and positive C3 DAT were identified. Acid eluate results from samples DAT positive for C3 alone were analyzed further. The eluate and serum results, transfusion history, and patient diagnosis of these samples were categorized. Clinically informative eluate results were defined as identification of an alloantibody or panagglutination/autoantibody in the acid eluate but not in the patient's serum.

Results/Findings:

Variations existed in elution performance between individual IRLs within the blood center’s system. In total 1171 samples DAT positive for C3 alone were identified and of those, only 321(27%) samples had an elution performed. Samples with a history of recent transfusion or unknown transfusion history represented 52%(169) of eluates. A nonreactive eluate was the most common result (221, 69%). Alloantibodies were identified in 19(6%) eluates and panagglutination/autoantibody was identified in 71(22%) eluates. Patient samples that identified a cold autoantibody in the serum and subsequently had a nonreactive acid eluate represented 40%(130) of all eluates prepared. Informative eluates were found in 30(9%) of the samples.

Conclusions:

Acid elutions performed on samples DAT positive for C3 alone were found to elicit clinically relevant results in only a small portion of samples. Current system wide IRL guidelines for elution performance do not differentiate between IgG and C3 DAT positive results. This ambiguity can lead to eluates being performed with no clinical value or missing clinically relevant results due to elution non-performance. Introducing elution performance guidelines based on transfusion history of less than 3 months, indicators of active hemolysis, and autoimmune activity concurrently in the serum for samples DAT positive for C3 alone could provide clinically significant results and lead to a reduction of uninformative acid elutions performed.