Clinical and immunologic features of adult primary antibody deficiency according to IVIGRT exposure.

BACKGROUND/AIMS: Primary antibody deficiency (PAD) in adults is increasingly recognized, but remains underdiagnosed and undertreated. We described the clinical and immunologic features of adult patients with PAD according to real-world exposure to intravenous immunoglobulin replacement therapy (IVIGRT) and explored whether the Ajou-PAD score reflects treatment decisions in routine clinical practice. METHODS: We conducted a retrospective cohort study at Ajou University Hospital (January 1, 2020-November 18, 2024), screening adults (age ≥ 18 yr) diagnosed with PAD, and excluding those with IVIGRT exposure before diagnosis. After 1:1 propensity score matching by age and sex, clinical and laboratory findings between the IVIGRT-exposed and -unexposed groups were compared. The discriminatory performance of the Ajou-PAD score, a composite index integrating clinical and immunologic parameters, was evaluated for IVIGRT exposure using receiver operating characteristic analysis. RESULTS: The final matched cohort included 602 patients (301 per group). Immunoglobulin G subclass 3 deficiency (IgG3SCD) was the most prevalent phenotype and more frequent in the IVIGRT-exposed group than in the IVIGRT-unexposed group. The Ajou-PAD score showed modest discriminatory performance for IVIGRT exposure (AUC = 0.61; 95% CI, 0.56-0.65). CONCLUSION: In Korean adults with PAD, IgG3SCD was the most prevalent phenotype and was more common among patients receiving IVIGRT in routine clinical practice. The Ajou-PAD score showed modest discriminatory performance for IVIGRT exposure and should be considered an exploratory adjunct rather than a standalone tool for treatment decision-making.