A new urinary test for stone "activity".

Rapid evaporation of urine to osmolarity 1200 results in a high incidence of envelope Wedellite and calcium phosphate crystals. The Wedellite crystals closely resemble those seen in untreated urine samples of stone formers. The incidence of crystalluria produced by these tests is higher in the stone formers than in the normal subjects, reduced by thiazides and increased by cellulose phosphate; combined thiazide and cellulose phosphate therapy was most effective in reducing crystalluria. Simple calcium and oxalate concentration products were calculated and did not correlate well with incidence of calcium oxalate crystalluria. Although the product is important, inhibitors of crystal formation must be equally important. It is postulated, but not proven, that the evaporation tests may indicate normal subjects at risk to stone formation when exposed to chronic dehydration and whether a stone former is still metabolically active.