Fasting Urinary Osmolality, CKD Progression, and Mortality: A Prospective Observational Study.

Area of Science:

• Nephrology
• Renal Physiology
• Biomarker Discovery

Background:

• Chronic kidney disease (CKD) involves impaired glomerular and tubular function.
• Assessing tubular function is crucial for determining CKD severity and progression risk.
• Urinary concentrating ability is a known indicator of kidney function.

Purpose of the Study:

• To investigate reduced urinary concentrating ability as a risk factor for CKD progression.
• To explore the association between fasting urinary osmolality and the decline in glomerular filtration rate (GFR) and end-stage renal disease (ESRD).

Main Methods:

• Prospective longitudinal cohort study of 2,084 adult CKD patients (stages 1-4).
• Fasting urinary osmolality measured by delta cryoscopy.
• Outcomes included ESRD, mortality, and measured GFR (mGFR) decline, analyzed using cause-specific hazards and linear mixed models.

Main Results:

• Lower baseline fasting urinary osmolality was significantly associated with a higher adjusted risk for ESRD (HR 1.97 for lowest vs. highest tertile).
• Patients with the lowest urinary osmolality showed a steeper decline in kidney function (-4.9% per year).
• No significant association was found between urinary osmolality and mortality before ESRD.

Conclusions:

• Fasting urinary osmolality may serve as a valuable tool for assessing nonglomerular damage in CKD.
• It can aid in identifying CKD patients at higher risk for progression, alongside GFR and albuminuria.
• Urinary concentrating ability is a relevant indicator for monitoring CKD severity and prognosis.