EFFECTS OF ACUTE ACID LOADING ON THE RISK OF CALCIUM-PHOSPHATE AND CALCIUM-OXALATE CRYSTALLIZATION IN URINE

The aim of this study was to examine the risk of calcium phosphate and calcium oxalate crystallization during acute acid loading under contr olled conditions. The effects of acute acid loading on rates of renal excretion of calcium, magnesium, phosphate, citrate, oxalate and urine pH were studied in healthy subjects. The risk of calcium phosphate an d calcium oxalate crystallization were evaluated by estimates of the i on activity products of calcium phosphate [AP(CaP)-index] and calcium oxalate [AP(CaOx)-index] according to Tiselius. In addition, the risk of brushite [AP(Bru)-index] crystallization was estimated. An acute ac id load administered as ammonium chloride (NH4Cl) produced increased u rinary excretion of calcium, phosphate and oxalate, decreased urinary excretion of citrate, and a decrease in urine pH. Consequently, calciu m-citrate-ratio in urine increased markedly in response to acid loadin g. AP(CaP)-index decreased markedly due to a fall in urine pH. AP(Bru) -index decreased slightly and remained low throughout the study. AP(Ca Ox)-index increased significantly, and acid loading is suggested as a risk factor for calcium oxalate stone formation.