Epidemiology of primary hypercalciuria

Primary hypercalciuria is a biochemical syndrome consisting of an exaggerated urinary excretion of calcium without any defined clinical cause. The figure of prevalence of hypercalci-uria in the population varies according to its definition and to some factors such as age, gender, race, and diet. Urinary ex- cretion of calcium is usually expressed in mg/24 hour with commonly accepted upper normal limits of 300 mg for men and 250 mg for women. The calcium/body weight ratio is an effective alternative to daily urinary output, with an upper limit of 4 mg/kg body weight/24 hour for both sexes. Finally hyper- calciuria can be defined by more than 0.15 mg calcium for mg of urinary creatinine in a 24-hour collection. Our previously unpublished data from a population study in- volving ealthy subjects from a village nearby Milan (Northern Italy) showed a prevalence of hypercalciuria, greater than 300 mg/24 h in men and 250 mg/24 h in women, of 12.5% (12% in males and 14% in females). In the same population, consider- ing a 0.15 urinary calcium to creatinine ratio as the upper limit of normal, the prevalence of hypercalciuria was 34% (26% in males and 42% in females), whereas, when the 4 mg/kg/day limit was considered, the rate was 18% (16% in males and 20% in females). The mean daily urinary calcium and the mean cal- cium/creatinine ratio were significantly higher in males than in females. The daily calcium output rose over the first two decades and remained constant during adult life in both males and females until the last two decades when it was significant- ly reduced in both sexes. On the contrary the highest values of alcium/creatinine ratio were observed in the first decade. The ratio felt over the second decade and it rose during the third and fourth decades remaining relatively constant until the last decades. There was no significant difference of the mean calcium/body weight ratio between males and females. The calcium/body weight ratio remained constant with age. Urinary calcium excretion seems to be influenced by dietary intakes of calcium, sodium, potassium, protein, and carbohy- drates although this relationship was not confirmed in opula - tions with a low intake of nutrient