Urinary Electrolytes: When is it Important to Estimate?


Dr Jayant Thomas Mathew, Kerala    09 January 2018

Proper interpretation requires integration with clinical data and an understanding of the appropriate uses for each test. Urine electrolytes cannot be interpreted in isolation. It requires concurrent serum electrolytes, including renal function and clinical information. Fractional excretion of sodium (FENa) is used in cases of acute oliguric renal failure to distinguish between prerenal azotemia and acute tubular necrosis. The FENa should not be used as a surrogate for the clinical assessment of volume status. In metabolic alkalosis, urine chloride concentration may be a better marker of volume status. When managing patients with hyponatremia, timely and repeated measurements of urine sodium concentration and osmolality must be used. Urine osmolality must be measured when evaluating a patient with polyuria to determine whether the polyuria is caused by solute diuresis or water diuresis. In cases of non-anion-gap metabolic acidosis, urine pH, sodium, potassium and chloride concentrations should be measured. For cases of hypokalemia, calculate a transtubular potassium gradient to help distinguish between gastrointestinal and renal loss of potassium.

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