Background and Clinical Significance: Sarcoidosis is a systemic inflammatory disorder characterized by noncaseating granulomas. While pulmonary involvement is common, isolated renal involvement is rare and diagnostically challenging. We report a case emphasizing the utility of urinary tubular markers for early detection. Case Presentation: A 60-year-old woman with a history of suspected ocular sarcoidosis presented with progressive renal impairment and constitutional symptoms. Initial workup for systemic sarcoidosis was negative, leading to a misdiagnosis of chronic fatigue syndrome. Her rising serum creatinine was initially attributed to dehydration. However, a marked elevation in urinary β2-microglobulin (33,736 μg/L) prompted a renal biopsy, which revealed granulomatous tubulointerstitial nephritis. Following prednisolone therapy, her renal function improved, and her fatigue resolved completely. Conclusions: This case demonstrates that the kidney can be the primary site for histological diagnosis in the absence of pulmonary lesions. Incorporating urinary β2-microglobulin into routine monitoring may facilitate the early detection of renal sarcoidosis, preventing diagnostic delays.
Keywords: interstitial nephritis; sarcoidosis; tubular markers; β2-microglobulin.