Clinical Significance of Positive Red Blood Cell Antibody Screen with Inconclusive Antibody Identification

The routine blood type and screen involves screening for unexpected antibodies, in addition to checking the ABO group and RH type. Most of these antibodies are IgM type, also known as nuisance antibodies. They are thought not to have much clinical significance. A positive antibody screen can sometimes be associated with inconclusive antibody identification. An inconclusive antibody screen is defined as test reactive for gel screen (which is a two cell screen) and no defined pattern on antibody identification panel.

American Association of Blood Banking states that if an antibody screen is positive, an attempt should be made to identify the antibody and cross match for the same along with ABO and RH. If the antibody screen is negative, they recommend only ABO/RH compatibility testing to be done before transfusion. However, there is great paucity of literature regarding the scenario where the antibody screen is positive but the antibody identification (ABID) is inconclusive, to see if this has any clinical implications. This study was undertaken to review the clinical implications of a positive antibody screen with inconclusive ABID.

All patients who had an antibody screen performed and the antibody identification was inconclusive during Jan 1^st 2005 to Dec 31^st 2010, were identified from the blood bank database of our hospital. The charts were then retrospectively screened for clinical diagnosis, antibody screen and ABID, repeat screen, blood transfusions given, if any, and occurrence of transfusion reactions. The patients were also studied for rise in hemoglobin per unit of red cell (excluding patients with active blood loss or hemolysis). Patients in the screened group who had a positive antibody identified in previous screening were excluded from the study group. The control group was composed of patients with a definite positive antibody screen with an identifiable antibody during the same period.

In our institution, the patients who have a positive antibody screen get a cross match by gel technology. We use Reagent Red Blood Cells 0.8% Selectogen (Ortho clinical Diagnostics) for two-cell screen and Reagent Red Blood Cells 0.8% Resolve panel A Antigram Antigen Profile (Ortho Clinical Diagnostics) for detection and defining pattern of antibodies.

A total of 149 patients were identified from the blood bank database, which were included in study group. 150 controls were selected as well who had identified antibodies. Subsequently 69 (46.3%) patients from the study group had a repeat antibody screen done at a later date and out of that, 16 (23.2%) patients had a definite antibody identified and in 33 (48%) patients the repeat antibody screen was negative. In 26% the repeat screen was also inconclusive. 38 patients received transfusions in the study group and 37 in the control group. The average rise in hemoglobin per unit of red blood cell was 1.1 g/dL in the study group and same 1.1 g/dL in the control group. One patient in the study group had a transfusion reaction compared to no transfusion reactions in the control group. The transfusion reaction in was in the form of delayed hemolytic reaction in this patient who was subsequently identified to have “Jka” antibody at a later date. This would equate to 0.7% of all patients with inconclusive screen and 6% of patients who would have an antibody identified on subsequent testing. There was no mortality related to blood transfusion in either group.

Patients who have an inconclusive ABID on antibody screen are usually ignored as having not much clinical significance. Our study indicates that although transfusion appears relatively safe in such patients, they can rarely have transfusion reactions, likely due to yet unidentified antibodies. Although 48% of patients retested will have a negative antibody screen, about a quarter of patients will have an antibody identified on subsequent testing. Hence, all patients with inconclusive ABID screen should be tested again, to identify if an antibody is present, in order to avoid any untoward reactions.

No relevant conflicts of interest to declare.