THE POLYURIA OF SOLUTE DIURESIS

Polyuria is an important symptom or sign because of its potential seve rity, diverse causes, and interesting pathophysiology. Whereas polyuri a induced by water diuresis is reasonably well understood and easily r ecognized by clinicians, that produced by solute diuresis is more like ly to cause confusion. In this article, we focus on solute diuresis as a cause of polyuria, review the classification and pathophysiology of polyuria, and describe the clinical and laboratory studies useful for the evaluation of the polyuric patient. A stepwise, logical approach is provided (1) to determine whether a patient has a water diuresis, a solute diuresis, or both (concurrently), and, (2) if a solute diuresi s is present, to determine if it is caused by electrolytes (eg, sodium chloride, sodium bicarbonate), by nonelectrolytes (eg, glucose, urea) , or by both. How to assess these possibilities and to determine the s pecific cause of the diuresis is discussed in detail. Three representa tive case examples are provided. Selected causes of a solute diuresis also are reviewed.