Urinary β2-microglobulin and disease activity in patients with tubulointerstitial nephritis and uveitis syndrome

BACKGROUND: Urinary β2-microglobulin (Uβ2M) is elevated in tubulointerstitial nephritis and uveitis (TINU) syndrome and has emerged as an important diagnostic tool. This study aims to determine whether Uβ2M correlates with uveitis activity in TINU. METHODS: Retrospective observational case series of nine patients with TINU and ≥ 30 days follow-up. Presenting symptoms, visual acuity, uveitis characteristics, follow-up, Uβ2M, serum creatinine (SCr), urinalysis, and renal biopsy results were collected. RESULTS: A correlation between Uβ2M and anterior chamber (AC) cell (r = 0.69, 95% CI 0.46–0.84), flare (r = 0.65, 95% CI 0.39–0.81), trended toward a stronger correlation than SCr and AC cell (r = 0.59, 95% CI 0.29–0.79), flare (r = 0.52, 95% CI 0.19–0.75). Uβ2M decreased over 1–2 years while SCr returned to normal within a few months. CONCLUSIONS: Uβ2M correlate with uveitis activity and trend down over the course of TINU. Uβ2M may serve as a useful tool in determining where patients are in their systemic disease course.