On the distribution of urine output in normally cycling women

Abstract

SummaryIt has been suggested that it is possible to monitor the menstrual cycle by measuring the concentration of urinary reproductive steroids. This neglects the variation in void volume and in urine production rate. In neither case has any systematic analysis been reported previously. Overnight urine samples were collected each day for one complete cycle by 24 women and the void volumes and intervoid times were recorded. The void volume and urine production rate were approximately lognormally distributed and the intervoid time was approximately normally distributed. Using these distributions we consider the implications of the variation in void volume and urine production rate for the comparison of the concentrations of a urinary analyte in two samples.

Expressing the quantity of urinary analytes: a discussion of some issues arising from the monitoring of the menstrual cycle

“…Each of us knows from personal experience that the volume of urine (V) can fluctuate considerably from void to void. Our own data indicate that the distribution of the volume of overnight urine samples tends to be positively skewed and ranges from about 50 mL to approximately 1 L [29] and other data have a similar distribution, although V can have an even greater range (Brown, Cooke and Blackwell, manuscript in preparation) and if, as is often the case, circumstance dictates that daytime rather than overnight samples are sometimes collected then the variation can be increased further. Based on our overnight data, two samples containing exactly the same quantity of an analyte can differ in concentration by about 20-fold just because of fluctuations in V [29].…”

“…The same is not true of the relationship between J A and u A (Brown, Cooke and Blackwell, manuscript in preparation). This is unsurprising given the inconsistent relationship between u A and s A , but it is also consistent with the fact that J V , the time averaged value of dV/dt, is not constant in most circumstances and nor is dV/dt [29]. This means that s A is more reliably estimated using J A rather than u A , but, despite this, it should not be assumed automatically that dF/dt = u A V/s A because ds A /dt need not be zero (15).…”

“…It is apparent from these data that u Cr can change significantly with very small changes in J V (the open squares in Figure 7A) or change very little despite relatively large changes in J V (the open diamonds in Figure 7A). In these subjects J V ranged from 0.3 to 3.075 L/24 h (equivalent to 13-128 mL/h), which is more limited than the 10-200 mL/h we have reported for overnight urine samples from women free to eat and drink ad libitum [29].…”

“…We have shown that the distribution of J V of overnight urine samples tends to be positively skewed and ranges from about 10 mL h -1 to approximately 200 mL h -1 [29]. Based on these data, for two samples having exactly the same analyte concentration J A can vary about 20-fold just because of fluctuations in J V [29]. Despite this, it is not uncommon to find reports in which J V is assumed to be constant [47], uniformly distributed [48] or normally distributed [49].…”