Prognostic Value of the Level of Urine Dipstick Proteinuria in Gastric Cancer in the Korean Population

Background/Objectives: Proteinuria, a marker of renal dysfunction, has been implicated in cancer risk, yet its role in gastric carcinogenesis remains underexplored in high-incidence populations. This study evaluated the association between urine dipstick proteinuria severity and gastric cancer incidence in a nationwide Korean cohort. Methods: We analyzed data from the Korean National Health Insurance Service–National Sample Cohort, including 220,941 adults aged > 40 years, without a diagnosis of cancer, who received health examinations in 2009. Proteinuria was classified by single dipstick testing as negative, 1+, or ≥2+. Participants were followed for a mean of 4.37 ± 0.49 years (965,601.2 person-years). Multivariable Cox proportional hazards models adjusted for age, sex, body mass index, systolic blood pressure, fasting glucose, LDL cholesterol, estimated glomerular filtration rate, smoking status, alcohol intake, and physical activity were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). Results: During follow-up, 1934 participants (0.88%) developed gastric cancer. A significant dose–response relationship emerged (p for trend = 0.037). In fully adjusted models, 1+ proteinuria conferred no significant risk increase (HR 1.10; 95% CI, 0.80–1.51), whereas ≥2+ proteinuria was associated with a 42% higher gastric cancer risk (HR 1.42; 95% CI, 1.00–2.02). Conclusions: Severe dipstick proteinuria independently predicts elevated gastric cancer risk in Korean adults. Integration of urine dipstick testing into gastric cancer screening protocols may offer a simple, cost-effective strategy for risk stratification, particularly in high-incidence settings.