Urine for Detection of Urinary Solids

The method used for the collection of luine to detect urinary solids is particularly sensitive to a variety of artifacts and variations in treatment (Cohen et al. 2007). Most of all, it is essential that the animals not be fasted or go without water during the period of collection of urine. Since the excretion of the substances that are included in formation of the urinary solids is dependent on their consmnption, fasting the animals changes the urine composition considerably and can lead to a condition in which the solids are no longer formed. Fiulhermore, urinary solids can be rapidly excreted in the mine and are not retained so if they are not being constantly formed anew, they will not be detected. This includes urinary tract calculi. Some calculi will be small enough that they will be excreted in the urine, or dissolve with the lowering of the concentration of the solute itself. Furthermore, many of these calculi are actually quite soluble in urine, such as uracil, and rapidly solubilize in the urine. 

Likewise, collection of fresh void mine specimens for examination of the urine for chemical composition is also strongly recommended (Cohen et al. 2007). It is the actual concentration of the substances, not the overall amoimt being excreted or its ratio to some normalizing substances such as creatinine that is the critical variable when evaluating urine for the potential formation of solids. The procedures just described for mine collection for evaluation of the presence of minary solids is in marked contrast to the way that urine is typically collected for assessment of renal function. Finthermore, we have found that examination of rodent urine with dipsticks can also lead to misleading results, particularly with respect to measurement 

We strongly recommend examination of urine immediately after collection using a microelectrode to determine pH, rather than using a dipstick. Also, for rodent urine, the Bradford method for assaying protein is preferable to biuret-based methodology (Cohen 1995). 

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