Is it anti-D or anti-LW? A brief synopsis of the biology of the LW blood group and the importance and differential laboratory methods to discriminate these specificities.

Introduction: The anti-LW antigen is not considered clinically significant. Yet, it can cause some challenges in differentiating it from the anti-D antigen in pretransfusion testing.

Methods: This case report discusses a 35-year-old patient with nonmalignant gastrointestinal complications who was identified as having anti-LW during pretransfusion testing. We provide a brief history of the LW system and discuss the laboratory methods used to distinguish anti-LW from anti-D.

Results: The patient's prior workup revealed an O RhD-positive blood type and an antibody compatible with anti-D. Auto-control and direct antiglobulin testing with anti-immunoglobulin G were only weakly positive, but the elution was negative. Red blood cell genotyping did not show any RhD variant. Current workup showed the patient's plasma reacting with both RhD-positive and RhD-negative group O cord blood and not reacting with RhD-positive dithiothreitol-treated cells, confirming anti-LW specificity.

Discussion: Clarifying an apparent confusion between a true anti-D and a mimicking anti-LW in pretransfusion blood bank testing remains the basis of providing clinically relevant component therapy. Understanding the basics of the LW Blood Group System serology is fundamental to appropriate problem solving.