The polyuria of solute diuresis

Polyuria is an important symptom or sign because of its potential severity, diverse causes, and interesting pathophysiology. Whereas polyuria induced by water diuresis is reasonably well understood and easily recognized by clinicians, that produced by solute diuresis is more likely 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 diuresis 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 specific cause of the diuresis is discussed in detail. Three representative case examples are provided. Selected causes of a solute diuresis also are reviewed.