Normal Ranges for Urine Sodium and Urine Osmolality
Normal urine osmolality ranges from 300-900 mOsm/kg, with the kidney capable of concentrating urine up to 1200 mOsm/kg during dehydration, while normal urine sodium varies widely depending on dietary intake and hydration status but is typically >30 mEq/L in euvolemic states. 1
Urine Osmolality Normal Values
The typical range for urine osmolality is 300-900 mOsm/kg in healthy individuals with normal hydration and renal function. 1
In states of dehydration, the kidneys can maximally concentrate urine to approximately 1200 mOsm/kg as a physiologic response to conserve water. 1
Urine osmolality interpretation must always be paired with serum osmolality (normal 275-295 mOsm/kg) to determine if the kidney is responding appropriately to the body's hydration status. 2, 1
Urine Sodium Normal Values
Urine sodium concentration does not have a single "normal" value because it varies dramatically based on dietary sodium intake, volume status, and renal function.
In euvolemic states with normal sodium intake, urine sodium is typically >30 mEq/L, reflecting the kidney's ability to excrete dietary sodium. 3
A urine sodium <30 mEq/L generally suggests volume depletion or avid sodium retention by the kidneys in response to hypovolemia. 3
In pathologic states like SIADH, urine sodium is characteristically elevated (>30 mEq/L and often much higher), with case reports documenting concentrations exceeding 130 mmol/L in severe cases. 3, 4
Clinical Context for Interpretation
When Evaluating Hydration Status
Serum osmolality is the primary indicator of hydration status, NOT urine osmolality. 1
Urine osmolality, urine specific gravity, and urine color have inadequate diagnostic accuracy for assessing hydration and should not be relied upon for this purpose. 2
Serum osmolality >300 mOsm/kg indicates dehydration requiring intervention, while <275 mOsm/kg suggests overhydration or SIADH. 2, 1
When Evaluating Hyponatremia
The combination of low serum osmolality (<275 mOsm/kg), inappropriately elevated urine osmolality (>300 mOsm/kg), and high urine sodium (>30 mEq/L) is diagnostic of SIADH. 3
In hypovolemic hyponatremia, urine sodium is typically <30 mEq/L as the kidneys attempt to conserve sodium. 3
Important Caveats
Urine sodium and osmolality must never be interpreted in isolation—they require simultaneous measurement of serum electrolytes, serum osmolality, and clinical volume assessment. 1, 3
In older adults, renal concentrating ability declines with age, making renal parameters less reliable indicators of hydration status. 1
Diuretic use, adrenal insufficiency, and various medications can significantly alter urine sodium excretion independent of volume status. 3
The persistence of very high urine osmolality (>500 mOsm/kg) and high urine sodium may predict poor response to fluid restriction in SIADH management. 4