Calcium oxalate aggregation in whole urine, new aspects of calcium stone formation and metaphylaxis.

Objectives: To assess the influence of pH, Ca(2+)-concentration, hydroxyapatite (HAP) and preformed calcium oxalate (CaOx) aggregates on the aggregation (AGN) of CaOx crystals directly produced in unpretreated whole urine (U) by oxalate loads (OL).

Methods: After OL at pH 5.0 and pH 6.5 minimal sedimentation time of precipitates (ST = minutes for 0.05 optical density [OD] decrease) was measured in 40 U of 5 healthy men by spectrophotometry. An ST(P) (< or =2.8) was taken as indicator for primary AGN and an ST(S) (< or =1.4) as one for secondary AGN. In 20 U Ca(2+) was determined initially, Ca(2+) at pH 6.5 was readjusted by adding CaCl(2) to the value measured at pH 5.0 and an OL of 1.5mM performed. OL of 0.25-0.75 mM were given to 20 U either with 0.05 mg/ml HAP or after a primary OL of 2mM.

Results: Alkalinization of U from pH 5.0 to 6.5 decreased Ca(2+) by 44+/-15% (mean+/-S.D.) and, in U with total Ca <3mM, below a crucial value of 1mM where no ST(P) was observed. At identical Ca(2+), pH had no influence on ST. With HAP, an ST(P) was found after an OL of 0.5mM in 10% and of 0.75 mM in 35%, predominantly at pH 5.0. An ST(S) was observed after a second OL of 0.5mM in 55% and of 0.7 5mM in 75% of experiments.

Conclusions: Provided that AGN is important for stone formation, calcium nephrolithiasis might be initiated at high urinary Ox and low pH by HAP of kidney calcifications, prevented at moderate calciuria by alkali treatment and augmented during relative hyperoxaluria by secondary AGN.