The study was carried out in order to investigate
citrate metabolism (i.e. serum levels, filtered load, tubular reabsorption, total and fasting urinary excretion) in a large group of normal subjects (n = 39) and
kidney stone patients (n = 45). We found that mean serum
citrate levels and filtered loads were similar in the two groups studied. On the other hand, both the 24-hour urinary
citrate and the fasting
citrate/
creatinine ratio were significantly reduced, whereas the mean tubular reabsorption of
citrate appeared to be significantly increased in
kidney stone patients in respect to control subjects. A good correlation was found between the fasting and the 24-hour
citrate/
creatinine ratio in both normal subjects (r = 0.84, p less than 0.001) and
kidney stone patients (r = 0.89, p less than 0.001). Our data indicate that the kidney appears to be involved in the pathogenesis of hypocitraturia in
kidney stone patients and that a substantial proportion of these patients show a reduced urinary excretion of
citrate. Finally, the evaluation of the fasting
citrate/
creatinine ratio may replace the measurement of the substance on the basis of a 24-hour urine collection.