CAN SPOT URINE SAMPLES REPLACE THE 24-H U RINE SPECIMEN IN THE METABOLIC EVALUATION OF STONE-FORMING PATIENTS

The gold standard for metabolic evaluation of stone-forming patients i s the 24-h urine specimen, Recently, some authors have suggested that for routine metabolic evaluation spot urine samples are as valuable as the 24-h urine specimen. The purpose of our study, was to determine t he value of the spot urine sample in comparison with the 24-h urine sp ecimens. Eighty-eight healthy volunteers on different diets were inves tigated (32 vegetarians, 12 body-builders without protein concentrates , 28 body-builders on protein concentrates, and 16 subjects on a regul ar European diet), Using 24-h specimens, excretion rates of oxalate, c alcium, sodium and potassium were determined, The concentration ratio of these electrolytes to creatinine was calculated for spot urine samp les. A highly significant correlation between the excretion rates and the results of the spot urine samples was found for all parameters. Ho wever, the correlations showed considerable variations, On the other h and, we were able to show that creatinine excretion is highly dependen t on daily protein intake, body weight and glomerular filtration rate. This leads to a considerable inter- and intraindividual variation in creatinine excretion, This variation of the creatinine excretion is th e major cause for the variation in the results of spot urine samples. It is concluded that spot urine samples are an inadequate substitute f or the 24-h urine specimen and that the 24-h urine specimen is still t he basis for metabolic evaluation in stone patients.