Positive neonatal direct antiglobulin test and free circulating panagglutinin due to high‐titer immunoglobulin G1 anti‐In b without in vivo hemolysis
Year: 2026
Type: article
Study design: Case Report
Abstract: Background The cluster of differentiation 44 glycoprotein carries the Indian blood group system, including the antithetical antigens In a and In b . The In b antigen is highly prevalent, with more than 99.9% of Caucasians being In b ‐positive, whereas In b ‐negative individuals are found almost exclusively in South Asian populations (~0.02%). Anti‐In b can cause hemolytic transfusion reactions, but little data are available on hemolytic disease of the fetus and newborn (HDFN), suggesting minimal placental transfer, with only one reported case of a positive neonatal direct antiglobulin test (DAT). Case Report A woman of Indian origin developed an anti‐In b alloantibody with a titer of 64 during her first pregnancy. This was detected only at delivery, with no evidence of transplacental transfer of antibodies or HDFN. The anti‐In b titer increased after delivery, reaching a peak of 1024, and remained stable throughout the second pregnancy. At birth, the second neonate showed a strongly positive DAT, with anti‐In b detectable in both the plasma and eluate, confirming transplacental transfer and red blood cell binding. Testing of maternal plasma showed immunoglobulin G1 predominance over immunoglobulin G3 and moderate‐to‐high hemolytic potential in the monocyte monolayer assay and antibody‐dependent cellular cytotoxicity (ADCC) test, with a monocyte index of 7.7–10% and ADCC of ~40%. Despite these findings, the neonate exhibited no signs of hemolysis. Conclusion This case demonstrates that high‐titer, functionally active maternal anti‐In b antibodies can coexist with neonatal anti‐In b reactivity without causing hemolysis. The marked discrepancy between serological, functional, and clinical findings underscores the limited predictive value of current assays in rare blood group incompatibilities.
Source: Transfusion
DOI: 10.1111/trf.70384
Institutions: German Red Cross, Swiss Red Cross, Goethe University Frankfurt
Language: English
Topic: Blood groups and transfusion
Subfield: Hematology
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W7204855896