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J Anal Toxicol. 2013 Jan-Feb;37(1):5-10. doi: 10.1093/jat/bks082. Epub 2012 Oct 26.

Effects of fluid load on human urine characteristics related to workplace drug testing.

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  • 1Bioaeronautical Sciences Research Laboratory, Civil Aerospace Medical Institute, Federal Aviation Administration, US Department of Transportation, Oklahoma City, Oklahoma 73125, USA.


During workplace drug testing, urine is tested for dilution, substitution and adulteration. Donors argue that these findings are due to medical, health or working conditions or diet and genetic differences. There is a paucity of data correlating changes in urine characteristics after a fluid load to various body parameters. Therefore, five urine specimens (one in the morning, one prior to drinking 800 mL of a beverage, and three time intervals thereafter) from 12 males and 12 females were tested for four different beverages on separate occasions. Of the 480 samples, 376 were in sufficient amounts. Of these 376, 36 (10%) had creatinine <20 mg/dL but ≥2 mg/dL; 27 (75%) of 36 had specific gravity <1.0030 but >1.0010. Thus, these 27 samples can be considered to be dilute; 20 (74%) of 27 were from females. For males with at least one dilute sample, body fat was 11% less and resting metabolic rate (RMR) was 29% more than males with no dilute samples (p > 0.05); for females with at least one dilute sample, height was 8% less and weight 20% less than females with no dilute samples (p > 0.05). Individuals with a higher RMR appear to have a greater potential for producing dilute urine specimens than those with a lower RMR. Thus, a dilute sample does not necessarily indicate that it was intentionally diluted. Such samples must be carefully evaluated in consideration with recent consumption of liquid by donors to avoid false accusations.

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