These results suggest a multifactorial aetiology for stone formation in renal transplant recipients. Approaches to prevention and management are discussed.

Quantitative and qualitative studies have been made of the urinary crystals from a series of normal subjects and from stone formers with idiopathic hypercalciuria with and without treatment with thiazide diuretics and/or cellulose phosphate. The results obtained from mid-morning unprepared subjects seemed more helpful than those obtained following overnight collections or after a dry breakfast. Crystalluria was more common in stone formers than in normal subjects, but was seen in both groups. The most striking difference between these 2 groups was the almost complete absence of aggregation of oxalate crystals in the normal subjects. Cellulose phosphate greatly reduced phosphate crystals but resulted in a large increase in small oxalate crystals but without change in the incidence of aggregation of oxalate crystals. Thiazides also reduced occurrence of phosphate crystals but only gave a very small increase in oxalate crystals and also without change in aggregation of oxalate crystals.

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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.