ACCURACY OF SOLID PHASE METHOD FOR THE DETECTION OF RBC ANTIBODIES OF TRANSFUSION RELEVANCE

Abstract

Background: Solid phase red cell adhearance (SPRCA) is a highly sensitive method applied for the screening and identification of red blood cell (RBC) irregular antibodies as well as for weak-D phenotype detection. The methodology can be performed under secure automation and selected by blood banks for the immunohematological routine of both blood donors and patients. Considering the high sensitivity of solid phase, concerns might rise referring to the risk of false positive results. In this scenario, determining the specificity and accuracy of SPRCA for antibody screening is important, as well as determining if the positive results represent antibodies of transfusion relevance. Aims: 1) To evaluate the accuracy of SPRCA for antibody screening and identification using samples of multitransfused patients, mainly with Sickle cell disease (SCD); 2) To determine the clinical relevance of antibodies of undetermined specificity (AUS) detected in SPRCA using the Monocyte Monolayer Assay (MMA). Methods: A comparative study was conducted comparing SRPCA (Capture, Echo Lumena®, Werfen, Barcelona) and gel test (Erytra Eflexis®, Grifols, Barcelona) for antibody screening and identification. Samples from previously investigated patients presenting with irregular antibodies directed to the most immunogenic blood group systems (Kell, MNS, Rh, Duffy, Kidd, Diego) were included in the analysis and tested in both assays (gel and SPRCA). In parallel, samples from patients without irregular antibodies were also tested. In case of AUS or antibodies detected only in SPRCA, MMA was performed. Results: Eighty samples were included in the study. In the group of patients with positive irregular antibody screening and identification (n = 60), 59 (98,3%) presented the same specificity of alloantibodies identified in both methodologies. One patient presented anti-E and anti-c in gel method (strength of agglutination 3+), but anti-E was not detected by SPRCA (IgM class). In the group of patients without RBC alloantibodies (n = 20), there was 100% concordance between SPRCA and gel method. Among all samples studied, three presented in both method antibodies of unknown specificity (AUS) after extensive serological workup. For these patients, RBC units were selected for transfusion based on extended-phenotype compatibility and both indirect antiglobulin test (IAT) crossmatch and MMA was performed. IAT crossmatch resulted incompatible in both SPRCA and gel test. Monocyte index resulted less than 5% in one sample and more than 5% in two samples (67%), the latter being considered as of clinical relevance. Interestingly, the intensity of agglutination observed in IAT-crossmatch using SPRCA correlated with MMA monocyte index. Also, in the cases in which anti-Jka (n = 3) or anti-Dia (n = 2) were identified, the intensity of agglutination was significantly higher in SPRCA. Even though SPRCA detects IgG-class antibodies, in two cases IgM antibodies (anti-M and cold autoantibody) were detected by the method indicating the antibodies possessed an IgG component. Summary/conclusions: SPRCA presented high accuracy in RBC antibody screening and identification, with no observed false positive results. Higher agglutination strength was observed in SPRCA for some antibody specificities, such as anti-Jka and anti-Dia, making the identification easier in cases of multiple antibodies. Among the antibodies of undetermined specificity identified, 67% had predicted in vitro transfusion relevance.