Calcium oxalate crystallization in undiluted postprandial urine of healthymale volunteers as influenced by citrate

The crystallization of calcium oxalate (CaOx) in undiluted urine of healthy male volunteers, collected 3 h after Intake of a test meal, was evaluated. In two experiments in vitro either the urinary total citrate concentration was Increased (urine A) or the urinary pH was elevated (urine B). In one c linical trial the bioequivalence of orally taken potassium citrate (PC) or potassium-sodium citrate (PSC) (n = 9) was studied, In two other trials the dose-response effects of oral PC (n = 8) and oral calcium-sodium citrate ( CSC; n = 6). Elevation of urinary citrate (urine A) decreased CaOx crystall ization (nucleation, growth, agglomeration time), the crystal content of ca lcium and oxalate was low and the one of citrate was high. Elevation of uri nary pH (urine B) also inhibited CaOx crystallization, the calculated molar ratio free (ionised) citrate/free (ionised) calcium at pH 7.0 was about tw ice the value observed at PH 5.5, and the ratio complexed citrate/complexed calcium was low. PC and PSC, leading to high urinary citrate and pH, inhib ited CaOx crystallization, the former at the stages nucleation, growth and agglomeration, the latter largely beyond nucleation. CSC increased calciuri a and crystal growth, but left crystal agglomeration time unchanged. The ur inary molar ratio total calcium/total citrate appeared to Indicate the stat e of crystallization, as influenced by alkali containing citrate. It was concluded that 1) application of a technically simple test allows to study CaOx crystallization in undiluted urine; 2) changes in urinary PH an d citrate manifest as altered CaOx crystallization, presumably inhibiting t his process, the stage of nucleation Included, via the action of free citra te and the formation of a calcium citrate complex (stoichiometry <3:2); 3) oral intake of PC, PSC or CSC modulate differently CaOx crystallization. Th e significance of these findings, especially with CSC, for renal stone risk Is uncertain, but awaits clarification by long-term studies using the desc ribed techniques and the calcium/citrate ratio In postprandial urine.