Diagnostic value of urinary sodium, chloride, urea, and flow.

Up to 30% of hospitalized critically ill patients may have a rise in serum creatinine concentration. In addition to history and physical examination, there is diagnostic value in assessing urinary electrolytes, solute excretion, and urine flow in these patients. The correct interpretation of these urinary parameters can avoid unnecessary volume overload and mechanical ventilation, risk factors for increased mortality in patients with rising serum creatinine. The present article also discusses the role of arterial underfilling in causing prerenal azotemia in the presence of an increase in total body sodium and extracellular fluid expansion. As with extracellular fluid volume depletion, arterial underfilling secondary to impaired cardiac function or primary arterial vasodilation can delay or prevent recovery from ischemic or toxic acute tubular necrosis. The present brief review discusses the various aspects of the correct interpretation of urinary electrolytes, solute excretion, and urine flow in the setting of a rising serum creatinine concentration.