Abstract
The urinary excretion rate is calculated based on short-term, defined time sample collections with a known sample mass, and this measurement can be used to remove the variability in urine concentrations due to urine dilution. Adjustment to the urinary excretion rate of hippuric acid was evaluated in 31 healthy volunteers (14 males and 17 females). Urine was collected as short-term or spot samples and tested for specific gravity, creatinine and hippuric acid. Hippuric acid values were unadjusted or adjusted to measurements of specific gravity, creatinine or urinary excretion rate. Hippuric acid levels were partially independent of urinary volume and urinary flow rate, in contrast to specific gravity and creatinine, which were both highly dependent on the hippuric acid level. Accordingly, hippuric acid was independent on urinary specific gravity and creatinine excretion. Unadjusted and adjusted values for specific gravity or creatinine were generally closely correlated, especially in spot samples. Values adjusted to the urinary excretion rate appeared well correlated to those unadjusted and adjusted to specific gravity or creatinine values. Thus, adjustment of crude hippuric acid values to the urinary excretion rate is a valid procedure but is difficult to apply in the field of occupational medicine and does not improve the information derived from values determined in spot urine samples, either unadjusted or adjusted to specific gravity and creatinine.
Highlights
Several methods are used to adjust urinary indices in spot samples according to the concentration/dilution of urine
The aim of the present study was to compare the adjustment of urinary levels of hippuric acid (HA), which is the main metabolite of toluene but can be measured in non-exposed subjects because it is a final metabolite of several substances, to specific gravity (SG) and creatinine with the adjustment to urinary excretion rate (UER)
Our data clearly show that the adjustment of HA, and likely all anionic organic compounds actively secreted by the tubule, to UER is reliable
Summary
Several methods are used to adjust urinary indices in spot samples according to the concentration/dilution of urine. The UER is uses short-term, defined time sample collections and is calculated by multiplying the analyte concentration in the urine by the volume of the void after bladder emptying and dividing by the duration of time the void accumulated in the bladder, assuming the bladder was completely emptied after each urination and that the entire sampling void volume is known [2]. This method is based on the mass sample and removes the variability due to the concentration/dilution of urine, for analytes that are affected by urinary flow [3]. Several analytes measured in occupational medicine are excreted immediately after exposure, indicating that 24-hour collections could lead to underestimation of the results [4,5]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
