Case report
Resolving an Unexpected Blood Grouping Discrepancy and a False-positive Compatibility Test in Pretransfusion Workup: A Case Report
ED07-ED09
Correspondence
Vidhi Jain,
C/15, Pancham Duplex, Parivar Char Rasta, Waghodia Road, Vadodara, Gujarat, India.
E-mail: vidhidjain269@gmail.com
Column Agglutination Technology (CAT), commonly known as the gel card method, is widely used in transfusion medicine for its sensitivity, standardisation, and reproducibility, but its heightened sensitivity can occasionally generate false-positive cross match results that present a diagnostic challenge in urgent settings. This report describes a 76-year-old man with symptomatic severe anaemia (haemoglobin 5.2 g/dL), cholelithiasis, and Acute Kidney Injury on Chronic Kidney Disease (AKI on CKD), who had been transfused approximately one month earlier and was referred for pretransfusion workup. Forward grouping identified the blood group as O, Rh-D positive, while reverse grouping by CAT initially showed mixed-field agglutination; a strongly positive anti-H lectin reaction excluded the Bombay (Oh) phenotype. CAT cross matching demonstrated persistent 4+ incompatibility against two separate O Rh-D positive units across two independent samples. All recognised causes of grouping discrepancy and cross match incompatibility were systematically evaluated, and the Direct Antiglobulin Test (DAT) was negative. Conventional Tube Technique (CTT) resolved the apparent grouping discrepancy, confirmed blood group O Rh-D positive without ABO discrepancy, and demonstrated full serological compatibility, thereby establishing a gel-specific false-positive result. One unit of O Rh-D positive Packed Red Blood Cells (PRBC) was transfused uneventfully; the patient subsequently died of his underlying illness during the same admission. This case underscores the importance of recognising false-positive CAT cross match results and the continued value of conventional tube testing as a confirmatory method, and highlights the need for clear standard operating procedures to prevent unnecessary withholding of serologically compatible blood from patients who urgently require transfusion.