# Serological and Clinical Evaluation of Incompatible Crossmatches Encountered in Pre-transfusion Testing

## TL;DR

This study examines the causes and patterns of incompatible blood crossmatches in transfusion testing, finding that alloantibodies are most common, with significant links to patient age and diagnosis.

## Contribution

The study provides new insights into the clinical and demographic associations of antibody types causing incompatible crossmatches in transfusion practice.

## Key findings

- Alloantibodies were the most frequent cause of incompatible crossmatches (52.1%).
- Autoantibodies were exclusively found in DCT-positive cases, while daratumumab interference occurred only in DCT-negative cases.
- Older patients showed contributions from all antibody categories, while younger patients predominantly had alloantibodies.

## Abstract

Background

Pre-transfusion testing is essential for preventing incompatible red cell transfusions and associated adverse reactions. Despite modern serological advancements, unexpected alloantibodies, autoantibodies, and monoclonal antibody interference continue to contribute to incompatible crossmatches. This study evaluates the serological patterns, clinical associations, and diagnostic considerations of incompatible crossmatches encountered in routine transfusion practice.

Methods

This cross-sectional study was conducted at a tertiary-care transfusion service of Swami Rama Himalayan University, Dehradun, India, over a duration of 18 months, from April 2023 to September 2024. Of 34,631 packed red blood cell (PRBC) crossmatches performed, 46 (0.13%) showing major incompatibility were included. Detailed clinical history, hematological parameters, and immunohematological testing, including Direct Coombs Test (DCT), Indirect Coombs Test (ICT), extended antibody panels, and daratumumab interference assessment, were performed. Associations between antibody category and clinical variables were analyzed using Chi-square/Fisher’s exact tests, with p < 0.05 considered significant.

Results

Among 46 incompatible crossmatches, alloantibodies were the most frequent antibody type (24; 52.1%), followed by autoantibodies (16; 34.8%) and daratumumab interference (6; 13.0%). DCT status showed a significant association with antibody type (p = 0.001), with autoantibodies observed exclusively in DCT-positive cases (16/16; 100%), while daratumumab interference occurred only in DCT-negative cases (6/6; 100%). Significant associations were observed for age group (p = 0.012), clinical diagnosis (p = 0.001), previous transfusion history (p = 0.001), number of PRBC units transfused (p = 0.001), hepatomegaly (p = 0.009), and splenomegaly (p = 0.001). Younger patients predominantly exhibited alloantibodies, whereas patients older than 50 years showed contributions from all antibody categories. Autoantibodies predominated in benign hematological disorders (12; 75.0%), while daratumumab interference was confined to hematological malignancies (6; 100%). Gender (p = 0.463) and Rh typing (p = 0.076) were not significantly associated with antibody distribution. Logistic regression analysis did not identify reliable independent predictors due to wide confidence intervals and model instability.

Conclusion

Most incompatible crossmatches were caused by alloantibodies, though clinically significant contributions from autoantibodies and daratumumab interference were also observed. Strong associations with demographic and diagnostic variables highlight the importance of individualized immunohematological assessment. Routine use of structured diagnostic algorithms can enhance resolution of incompatible crossmatches and strengthen transfusion safety.