Abstract
<title>Abstract</title> <p> <bold>Background</bold> Tubulointerstitial nephritis and uveitis (TINU) syndrome is an uncommon cause of acute tubulointerstitial nephritis in children, and early <bold>-</bold> stage disease is rarely recognized because kidney and ocular manifestations often appear asynchronously. Japan’s nationwide school urinalysis screening program provides a unique opportunity to detect asymptomatic tubular abnormalities, including isolated glycosuria, although urinary β2 <bold>-</bold> microglobulin (β2MG) is not routinely measured. <bold>Methods</bold> We describe two 14 <bold>-</bold> year <bold>-</bold> old girls in whom asymptomatic glycosuria detected during school urinalysis screening led to the early identification of TINU syndrome. To contextualize these findings, we also reviewed four <bold>-</bold> years of regional data from 209 glycosuria <bold>-</bold> positive students to evaluate current screening practices. <bold>Results</bold> Both patients exhibited isolated glycosuria with normal blood glucose and markedly elevated urinary β2MG. Targeted questioning revealed subtle ocular symptoms, and ophthalmologic evaluation confirmed anterior uveitis. Kidney function remained normal, and neither patient required systemic therapy. Urinary abnormalities normalized sequentially, with β2MG/creatinine returning to the reference range after 22 weeks and 14 months, respectively. Among 209 glycosuria <bold>-</bold> positive students, 38 were diagnosed with renal glycosuria, and urinary β2MG was measured in just 5 (13%). Two additional students were suspected of having missed tubulointerstitial nephritis. <bold>Conclusions</bold> These cases capture the earliest detectable phase of TINU syndrome—isolated glycosuria with elevated urinary β2MG—identified before the onset of kidney dysfunction or overt ocular symptoms. Our findings highlight the importance of considering tubular injury in children with glycosuria and support incorporating urinary β2MG measurement into the evaluation of glycosuria <bold>-</bold> positive students to avoid delayed diagnosis of TINU‑associated uveitis. </p>