Background/Purpose: Rituximab, a monoclonal antibody which binds to the CD20 antigen of B cells, is used in the treatment of many rheumatologic conditions. Due to its mechanism of action, which depletes B cells and reduces production of immunoglobulins, patients who receive rituximab are at significantly increased risk of developing hypogammaglobulinemia. Studies suggest that as many as 38% of patients who receive rituximab develop hypogammaglobulinemia, which in turn places them at increased risk of recurrent infection (Casulo et al., 2014). A reduced baseline level of immunoglobulins is associated with severe infections after receiving rituximab. Current literature suggests that patients should therefore be pre-screened with quantitative measurement of immunoglobulins prior to initiation of rituximab (Buch et al., 2011). In this study, we aimed to assess the prevalence of this pre-screening in a large academic health center.

Methods: We conducted a retrospective cohort study based on electronic health records in a large academic health system. Adults (≥18 years) who received their first rituximab dose between 1/1/2023 and 12/1/2024 were included. Baseline screening was defined as any recorded quantitative immunoglobulin panel drawn in the six months prior to initiation of rituximab. IVIG administration ≤ 6 months after initiation (follow‑up through 1 May 2025) served as a proxy for clinically significant antibody failure. Screened and unscreened groups were compared with Fisher’s exact test.

Results: Among 238 patients who started rituximab, only 115 (48.3 %) underwent guideline‑recommended baseline Ig screening, leaving 123 (51.7 %) unscreened. All screened patients had normal IgA and IgM levels. Quantitative IgG levels were not available. IVIG rescue occurred in 17 patients (7.1 %) overall—11/115 (9.6 %) in the screened group and 6/123 (4.9 %) in the unscreened group (p=0.21).

Conclusion: Despite guideline recommendations, over half of patients did not receive baseline Ig screening in the 6 months before rituximab initiation. No screened patient with abnormal IgA/IgM proceeded to treatment, indicating that screening—when performed—effectively excludes overt hypogammaglobulinemia. Interestingly, however, early IVIG rescue did not differ significantly between screened and unscreened patients, calling into question the short‑term protective value of current screening practice. Limitations include the absence of quantitative IgG data and single‑center design. Future work includes assessing screening rates and clinical outcomes across multiple sites and launching a quality‑improvement initiative using an electronic Best Practice Advisory to improve adherence.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/quantitative-immunoglobulin-screening-prior-to-rituximab-initiation-a-retrospective-cohort-study/