Kidney Health Biomarkers and Estimated Glomerular Filtration Rate Among Indonesian Tofu Production Workers: A Pilot Cross‐Sectional Study

ABSTRACT Background and Aims Small‐scale food‐production workers may experience heat strain, dehydration, and combustion‐related exposures, but evidence on early kidney injury in these settings remains limited. This pilot study aimed to describe serum and urinary kidney injury molecule‐1 (KIM‐1) and neutrophil gelatinase‐associated lipocalin (NGAL) profiles and to assess, exploratorily, whether these biomarkers discriminated an estimated glomerular filtration rate (eGFR)‐defined kidney‐function category among Indonesian tofu production workers. Methods A cross‐sectional complete‐case analysis included 32 workers from small‐scale tofu production units in East Java, Indonesia. Serum creatinine, serum and urinary KIM‐1, and serum and urinary NGAL were measured using laboratory microplate‐based assays. eGFR was calculated using the CKD‐EPI creatinine equation; < 90 mL/min/1.73 m 2 was a study‐defined exploratory category, not a CKD diagnosis. Descriptive statistics, Mann–Whitney U tests, Spearman correlations, and receiver operating characteristic analysis with 2000‐resample bootstrap 95% confidence intervals were performed. Results Ten of 32 workers (31.3%) had eGFR < 90 mL/min/1.73 m 2 , and four of 32 (12.5%) had serum creatinine above the laboratory threshold. Median KIM‐1 and NGAL concentrations were lower in the eGFR < 90 group across all four biomarker measures. Discriminatory performance was limited, with area‐under‐the‐curve values ranging from 0.327 to 0.416. Urinary KIM‐1 and NGAL were analysed as absolute concentrations without urinary creatinine normalisation; hydration‐related variation in urine concentration may have increased measurement variability and weakened observed associations and discrimination. With 32 workers and 10 eGFR < 90 observations, the AUC estimates are imprecise and not definitive measures of diagnostic performance. Conclusion KIM‐1 and NGAL showed limited discrimination of the study‐defined eGFR < 90 category; this result does not indicate poor overall utility as tubular injury biomarkers. Larger exposure‐informed studies should incorporate creatinine‐normalised urinary biomarkers, albuminuria, repeated kidney‐function measurements, and objective assessment of heat and nephrotoxic exposures.