Urinary electrolytes, solutes, and osmolality.

Urine chemical analysis can extend "beyond the dipstick" with an understanding of renal physiology and expected changes in electrolyte and solute handling. Urine electrolytes, such as sodium and chloride, can be helpful in discerning prerenal azotemia from acute renal tubular damage, which occur secondary to nephrotoxins or ischemia. Urine osmolality also is essential in determining appropriate antidiuretic hormone action and renal water handling. Urine solutes, such as albumin and brush border enzymes, may be more sensitive than plasma markers for early renal dysfunction. This article reviews these topics and the use of "extended" urine indices in veterinary medicine.