Investigating discrepancies and false positives in immunohematology tests using gel cards: insights from a case study on antibodies targeting the gel card matrix.

Abstract

Introduction: Discrepancies in gel card immunohematologic testing can result in false-positive reactions, making detecting antibodies and performing crossmatching difficult. Such unexpected reactivity may result from interactions with test system components, including the column matrix, chemicals, or reagents, rather than true antigen-antibody binding. Accurate identification and resolution of these discrepancies are crucial to prevent delays in transfusion and ensure patient safety.

Methods: This case involved a 24-year-old patient with sickle cell disease who required a blood transfusion, highlighting the diagnostic challenges posed by variability in gel card platforms. Blood grouping was performed using Tulip gel cards (Tulip Diagnostics, Pvt Ltd).

Results: The forward grouping was AB positive, but the reverse grouping showed pan-positive results. Repeat grouping by the gold standard-the conventional tube technique-resolved the discrepancy, and the blood group was identified as AB positive. Antibody screening (ABS) and autoantibody testing using Tulip gel cards showed pan-positive reactions, although the direct antiglobulin test was negative. However, conventional tube techniques for ABS and thermal amplitude tests for autoantibodies were negative. Crossmatching of phenotype-matched packed red blood cell units showed incompatibility on Tulip gel cards but compatibility using the conventional tube technique. The possibility of antibodies against enhancement media, such as low-ionic-strength solution, was ruled out after repeat testing with normal saline and phosphate-buffered saline, which showed negative reactions in different immunohematology tests. Due to suspected interference from the gel card components, crossmatching, ABS, and autoantibody testing were repeated using Bio-Rad gel cards, which showed compatible results.

Discussion: The false-positive reactions were attributed to antibodies against materials in Tulip gel cards, including silica-based microbeads, polyvinyl alcohol, and other stabilizers that are absent in Bio-Rad gel cards. This case underscores the importance of multiplatform validation, reagent standardization, and conventional tube testing in resolving immunohematologic discrepancies and ensuring safe transfusion practices.