Serum Osmolality as a Predictor of Renal Function Decline: A Retrospective Cohort Study

Background and Aims: Dehydration is a prevalent and costly healthcare concern, linked to heightened risks of acute kidney injury and in-hospital mortality. Despite its significance, limited evidence exists regarding its prevalence and correlation with renal function decline in apparently healthy individuals. This retrospective cohort study aimed to investigate the prevalence and association of dehydration with renal function decline and the development or progression of chronic kidney disease (CKD) in the general population. Methods: The medical records of subjects undergoing annual health check-ups from 2016 to 2019 at a single center in Taiwan were analyzed, and those with CKD stage V, insufficient data, or an increased estimated glomerular filtration rate (eGFR) were excluded. Serum osmolality, eGFR, and relevant parameters were measured. Logistic regression and Kaplan-Meier analyses were used to assess associations between osmolality and CKD-related outcomes. Results: Among the 4449 eligible subjects, those in the higher osmolality quartiles had an elevated risk of CKD or CKD progression. Multivariate analyses identified age, systolic blood pressure, serum osmolality, uric acid, proteinuria, and a history of diabetes as independent risk factors, with high-density lipoprotein being protective. Cumulative incidence curves demonstrated a significant increase in the risk of CKD with increasing osmolality levels. Restricted cubic spline analyses confirmed a nonlinear relationship between osmolality and CKD risk. Conclusions: Elevated serum osmolality independently predicted renal function decline and CKD development in apparently healthy individuals, and this effect persisted after adjusting for established risk factors. Our findings underscore the importance of addressing dehydration as a modifiable risk factor for CKD.