The urine volume measurement is used to ensure that a 24-hour urine collection has been done properly. There is no normal value for urine excreted over a 24-hour period, as this is highly dependent on the amount of liquid that was consumed during the period and the amount of water that was lost in the form of sweat, stool or air exhaled from the lungs. Generally, specimen amounts range from one to two litres. It is important that the 24-hour collection include only one first morning urine, usually at the end of collection period. Urine volume is used to determine excretion amounts per day (24-hour period) for the requested parameters (calcium, creatinine, protein, cortisol, etc.).
The creatinine excretion measurement in millimoles per day (mmol/d) complements the information provided by the volume measurement. In cases where the volume or the excretion of creatinine seem to indicate an incomplete collection or one exceeding the 24-hour period, results could skew high (period exceeding 24 hours or including two first morning urine samples) or low (loss of one or more urinations).