Urinary β2-microglobulin as a Potential Biomarker for Early Treatment Selection: A Patient with Severe IgG4-related Tubulointerstitial Nephritis

This case report describes an 80-year-old man with severe immunoglobulin G4-related tubulointerstitial nephritis (IgG4-TIN), characterized by storiform fibrosis with diffuse lymphocytic and plasma cell infiltration observed on a renal biopsy. Steroid pulse therapy administered immediately after confirming a remarkable increase in urinary β2-microglobulin (100,948 μg/L) along with no evidence of malignancy significantly improved the renal function and reduced the urinary β2-microglobulin levels. This study highlights the potential utility of urinary β2-microglobulin as a biomarker for early treatment selection in severe IgG4-TIN and emphasizes the need for timely intervention to prevent irreversible kidney damage.