urineNa

Urine sodium, abbreviated urine Na or UNa, is the concentration of sodium ions in urine, typically reported in milliequivalents per liter (mEq/L). Clinically, UNa helps assess how the kidneys handle sodium and the patient’s current intravascular volume status. In addition to spot measurements, a 24-hour urine collection provides the total daily sodium excretion (U-Na) in mEq/day, reflecting dietary intake and renal losses.

Normal ranges vary with diet and hydration. A healthy adult on a typical diet usually excretes about 100–260 mEq of sodium per day in 24 hours. Spot urine Na shows wide variability and is influenced by recent salt intake, hydration, and time of day.

In clinical practice, UNa and related calculations aid in evaluating acute kidney injury and disorders of fluid balance. The fractional excretion of sodium (FENa) is commonly used: FENa = (Urine Na × Plasma Cr) / (Plasma Na × Urine Cr) × 100. A FENa below 1% suggests prerenal azotemia; above 2% suggests intrinsic renal injury such as acute tubular necrosis. Diuretics can raise UNa and confound FENa interpretation; in such cases, FE Urea may be more reliable.

Urine Na also informs hyponatremia workups and volume assessment. Low UNa (<20 mEq/L) is typical of hypovolemia with extrarenal sodium loss, whereas higher UNa can be seen in euvolemic or hypervolemic states (e.g., SIADH, heart failure), depending on intake and renal response.

Interpretation should consider collection method, timing, medications (notably diuretics and ACE inhibitors), and overall renal function. UNa is one tool among several for evaluating kidney function and electrolyte disorders.