Abstract
This letter raises an important point regarding our study: is acidification of urine samples necessary to keep the calcium concentration stable during collection, i.e. prevent calcium precipitation, as well as after collection, i.e. solubilize precipitated calcium and prevent further precipitation? To address this question, we compared urine collections from 17 subjects in acidified and non-acidified bottles alternatively over a 24-h period. The mean (standard deviation) and range of the urine calcium concentrations for the acidified and non-acidified samples were 2.89 (1.82), 0.6–8.0 and 2.85 (1.75), 0.6–7.8 mmol/L, respectively, and were not significantly different (P = 0.45). These data suggest that acidification is not necessary for the accurate determination of urine calcium concentration. However, it must be appreciated that other factors such as urine phosphate, citrate and pH may also affect the precipitation of calcium in urine.
DECLARATIONS