The study by Martinez Valenzuela and colleagues addresses an important and clinically unresolved aspect of ANCA-associated vasculitis (AAV): how to interpret persistent immune activity during remission in patients receiving maintenance therapy.1 By focusing on the longitudinal behavior of serum calprotectin and urinary soluble CD163, the authors move beyond cross-sectional assessments and contribute data that are directly relevant to day-to-day monitoring decisions in nephrology and vasculitis clinics.

A notable strength of this work lies in its emphasis on biomarker dynamics during stable remission rather than during overt disease activity. The observation that both calprotectin and urinary CD163 continue to evolve over time, despite a Birmingham Vasculitis Activity Score of zero, reinforces the concept that clinical remission may not equate to complete immunological quiescence.2 This temporal dissociation has meaningful implications, as treatment decisions in remission are often binary continue or withdraw immunosuppression without reliable tools to capture smoldering disease biology. The data presented here suggest that serial biomarker trajectories may offer additional granularity beyond static thresholds.

The differential associations observed between the two biomarkers and clinical parameters merit particular attention. Serum calprotectin showed a consistent relationship with renal function indices, whereas urinary CD163 appeared more closely aligned with relapse risk, albeit modestly. This divergence supports the biological premise that these markers reflect distinct inflammatory compartments—systemic neutrophil–monocyte activation versus macrophage-driven renal inflammation. From a clinical perspective, this argues against reliance on a single biomarker and instead favors an integrated, pathway-informed interpretation when assessing residual disease activity in remission.

An especially relevant contribution of the study is the analysis of treatment-related effects on biomarker behavior. The finding that serum calprotectin levels vary according to the timing of rituximab administration, while urinary CD163 remains comparatively stable, underscores the need to contextualize biomarker values within therapeutic exposure. In patients receiving B-cell-depleting therapy, elevations in neutrophil-derived markers may reflect treatment-induced immune perturbations rather than disease reactivation.3 This distinction is critical, as misattribution could lead to unnecessary treatment escalation or premature retreatment.

The exploratory comparison with patients previously treated with mycophenolate mofetil further strengthens the argument that maintenance strategy itself shapes biomarker kinetics. Although not designed for formal comparative inference, the contrasting stability of biomarker levels in this group provides a useful clinical reference and highlights the complexity of interpreting immune markers across different therapeutic contexts.

Finally, this study raises a broader conceptual question regarding current remission definitions in AAV. The continued decline or fluctuation of biomarkers long after clinical remission suggests that existing frameworks may insufficiently capture ongoing immune processes relevant to long-term organ damage and relapse risk.4 Incorporating longitudinal biomarker patterns into remission assessment could refine risk stratification and support more individualized maintenance strategies.

In summary, this work provides valuable insight into the nuanced behavior of calprotectin and urinary CD163 during remission and emphasizes the importance of temporal, treatment-aware biomarker interpretation. These findings may help inform future efforts to align immunological monitoring more closely with clinical decision-making in AAV, ultimately improving long-term renal and patient-centered outcomes.