C4A and systemic lupus erythematosus: The underlying immunopathogenesis differs markedly: SLE‐associated DAH is typically driven by immune complex deposition with complement consumption, reflected in high anti‐dsDNA titres and low C3/C4 levels, while MPA‐related DAH results from pauci‐immune capillaritis triggered by MPO‐ANCA–mediated neutrophil activation.