Kidney-Related Screening Indicator Trends in Korea: 2010-2024 (eGFR, 2012-2024) and 2025-2028 Forecasts Using...

Background and Objectives: Chronic kidney disease (CKD) risk classification depends on reduced estimated glomerular filtration rate (eGFR) and kidney-damage markers such as albuminuria or proteinuria. National screening statistics can identify population-level signals-referred to here as screening-based kidney risk indicators and abnormal screening prevalence-that serve as proxy indicators rather than confirmed CKD diagnoses, and require confirmatory testing when abnormal. Materials and Methods: This retrospective repeated cross-sectional ecological trend study analyzed National Health Insurance Service (NHIS) health-screening aggregate tables distributed through the Korean Statistical Information Service (KOSIS), representing individuals who underwent NHIS health screening rather than all insured individuals. Age- and region-stratified tables for eGFR, serum creatinine, urine protein, triglycerides, and hemoglobin were used. Non-eGFR indicators covered 2010-2024 and eGFR covered 2012-2024. Operational endpoints were eGFR < 60 mL/min/1.73 m², serum creatinine ≥ 1.5 mg/dL, dipstick proteinuria ≥ 1+, triglycerides ≥ 150 mg/dL, and sex-specific anemia proxy; triglycerides and the anemia proxy were treated as associated metabolic/hematological indicators rather than kidney-specific endpoints. Crude national trends were supplemented with direct age-standardization (to the 2024 screening population) for eGFR, creatinine, proteinuria, and triglycerides, and with sex-stratified trends for all indicators. Binomial logit generalized linear models with calendar year as the predictor generated 2025-2028 forecasts; forecast reliability was assessed by temporal hold-out validation (fitting through 2020, predicting 2021-2024) and a recent-window (2018-2024) sensitivity analysis, and 95% bootstrap prediction intervals were derived by resampling model residuals and parameter uncertainty. Regional ecological correlations were assessed by Pearson and Spearman methods. Results: Dipstick proteinuria ≥ 1+ increased from 2.20% (age-standardized 2.34%) in 2012 to 3.71% in 2024 and was forecast to reach 4.64% (95% bootstrap prediction interval [PI], 4.50-4.83%) in 2028. eGFR < 60 decreased from 4.13% (age-standardized 5.20%) in 2012 to 3.43% in 2024, with a 2028 forecast of 3.06% (95% PI, 2.88-3.27%); the age-standardized decline was steeper than the crude decline, indicating the finding is not an artifact of population aging. Hold-out validation supported the eGFR, creatinine, and proteinuria forecasts (mean absolute error 0.05-0.14 percentage points) but showed poor fit for triglycerides and the anemia proxy, whose forecasts are reported as exploratory only. In 2024, eGFR < 60 reached 41.61% among persons aged ≥ 85 years. Jeonnam had the highest crude regional eGFR < 60 prevalence (5.09%), though regional comparisons could not be age-standardized. Regional eGFR < 60 was strongly correlated with elevated serum creatinine (Pearson r = 0.954, p < 0.001), reflecting their mathematical dependence rather than independent validation, and moderately correlated with the anemia proxy (Pearson r = 0.611, p = 0.009). Conclusions: NHIS/KOSIS screening data showed an age-standardization-robust upward proteinuria signal and persistent age-concentrated kidney function abnormalities. The findings support confirmatory testing after abnormal screening results and targeted kidney-risk follow-up, but they should not be interpreted as confirmed CKD incidence or prevalence.