Characterization of Creatinine Concentration in Urine Samples Taken for Occupational Exposure Monitoring

Urine samples that are given as spot or collection samples during working hours are used to assess occupational exposure to internal radiation or toxic heavy metals. In order to take into consideration the various metabolite concentrations in different urine samples, creatinine concentration is also measured and used for 24-hours normalization.

A study that was conducted at the NRCN included an investigation of the difference between urine creatinine concentration, measured by a photometric assay, for 341 spot urine and 786 urine collection samples of male workers, given during winter and summer. The geometric mean of creatinine concentration in the urine spot samples was 107.22 mg/dl with a geometric standard deviation of 1.72 while the geometric mean of urine collection samples was 84.15 mg/dl with a geometric standard deviation of 1.59. No significant differences were noticed between the creatinine concentration in samples that were given in summer and winter both in spot and in urine collection samples. On the other hand, a t-test analysis showed significant differences between urine creatinine concentration in spot and collection urine samples.

Based on this research, it is concluded that: 1. There are no seasonal effects on creatinine concentration values in urine spot and urine collection. 2. There is a significant difference between creatinine concentration in spot and collection urine samples.

One approach that should be considered, given the variability in urine creatinine concentration between workers, is to take a true 24 hours collection from each worker and to use the measured daily creatinine content in urine as the individual value for this worker.