Hierarchical organ aging signatures from routine abdominal CT add incremental disease risk stratification beyond blood biomarkers

Biological aging is heterogeneous across organ systems, yet whether CT-derived abdominal aging provides prognostic value beyond routine clinical data — and whether organ decomposition adds beyond a unified estimate — remains untested. We developed and evaluated organ-specific and ensemble biological age models from radiomic features across five abdominal organs in 68,682 CT scans from 32,882 subjects, evaluated on alignment with chronological age of healthy subjects (nested cross validation: MAE=3.68 years, R²=0.90). Age-interaction analyses showed attenuation of relative BAG–disease associations with advancing chronological age. We therefore performed focused prevention-oriented analyses in adults aged 20–60 years, the age range in which relative risk stratification was strongest. In this stratum, ensemble biological age gaps provided incremental prognostic value beyond demographic covariates for all-cause disease and mortality (ΔC-index=0.141, 0.051) and beyond routine blood biomarkers (ΔC=0.048), suggesting that CT-derived aging captures structural information complementary to selected blood markers. Organ-specific biological age added incremental prognostic value beyond ensemble selectively for focal diseases: cardiovascular (aorta, ΔC=0.091) and hepato-pancreatic (pancreas, ΔC=0.096). These findings establish a hierarchical organization of CT-derived biological aging, positioning routine CT as a source that adds prognostic value to existing clinical biomarkers.