The defined HHS/DOT substituted urine criteria validated through a controlled hydration study.
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This controlled hydration study was designed to validate the substitution criteria used by the Substance Abuse and Mental Health Services Administration (SAMHSA) to classify a workplace urine specimen as inconsistent with normal human urine. Study participants (n = 56) ingested at least 80 oz (2370 mL) of fluid over a 6-h period, 40 oz during the first 3 h (DOT hydration protocol) and 40 oz during the second 3-h period. Urine specimens (n = 498) were collected upon awakening, just prior to hydration, at the end of each hour of the 6-h test period, and upon awakening the next day. No urine specimen satisfied the paired substitution criteria of urine creatinine < or = 5.0 mg/dL and specific gravity < or = 1.001 or > or = 1.020. Seventy-three percent of the participants produced at least one specimen meeting the criteria for dilute urine: urine creatinine < 20.0 mg/dL and specific gravity < 1.003. Fifty-five percent of the participants produced at least one dilute urine specimen during the first 3 h of hydration. In conclusion, this controlled hydration study supports the criteria set by SAMHSA for classifying a specimen as substituted (inconsistent with normal human urine). (+info)
Evaluation of freezing point depression osmolality for classifying random urine specimens defined as substituted under HHS/DOT criteria.
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This study evaluates the analytical performance characteristics of freezing point depression osmolality in urine and osmolality as a suitable analytical indicator for determining the concentration of urine specimens submitted for workplace drug testing. Specifically, this study attempted to determine the utility of urine osmolality to serve as an indicator of substitution as defined by HHS/SAMHSA criteria. Urine osmolality was validated by determining the accuracy, precision, analytical sensitivity, reportable range, and reference interval for the method. Osmolality was measured in workplace urine specimens (n = 66) with creatinine concentrations < or = 5.0 mg/dL. Comparing the results with the lower limit of the random urine reference intervals for specific gravity (1.002) and osmolality (50 mOsm/kg), 62% had specific gravities < or = 1.001, 52% had osmolalities < 50 mOsm/kg, and 47% had both a creatinine < or = 5.0 mg/dL, specific gravity < or = 1.001 and an osmolality < 50 mOsm/kg. Urine specimens (n = 311) were collected from 35 volunteers enrolled in a controlled water loading study in which at least 80 oz (2370 mL) of fluid was ingested over a 6-h period. The lowest achieved osmolality was 28 mOsm/kg. Polyuria disorders have produced abnormally low urine osmolalities (lowest reported 18 mOsm/kg) but osmolalities < or = 23 mOsm/kg have resulted in death from water intoxication. An osmolality substitution cut-off to delineate a specimen as inconsistent with normal human urine can be set at some value < 50 mOsm/kg, when used in a population of individuals with urine creatinine concentrations < or = 5.0 mg/dL. (+info)
Fluid losses and hydration status of industrial workers under thermal stress working extended shifts.
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AIMS: To assess whether workers under significant thermal stress necessarily dehydrated during their exposure and whether "involuntary dehydration" was inevitable, as supported by ISO 9866 and other authorities. Other objectives were to quantify sweat rates against recommended occupational limits, to develop a dehydration protocol to assist with managing heat exposures, and to understand the role of meal breaks on extended shifts in terms of fluid replacement. METHODS: A field investigation to examine the fluid consumption, sweat rates, and changes in the hydration state of industrial workers on extended (10, 12, and 12.5 hour) shifts under significant levels of thermal stress (wet bulb globe temperature (WBGT) >28 degrees C) was conducted on 39 male underground miners. Urinary specific gravity was measured before, during, and at the completion of the working shift. Environmental conditions were measured hourly during the shift. Fluid replacement was measured during the working periods and during the meal breaks. RESULTS: Average environmental conditions were severe (WBGT 30.9 degrees C (SD 2.0 degrees C), range 25.7-35.2 degrees C). Fluid intake averaged 0.8 l/h during exposure (SD 0.3 l/h, range 0.3-1.5 l/h). Average urinary specific gravity at start, mid, and end of shift was 1.0251, 1.0248, and 1.0254 respectively; the differences between start and mid shift, mid and end shift, and start and end shift were not significant. However, a majority of workers were coming to work in a moderately hypohydrated state (average urinary specific gravity 1.024 (SD 0.0059)). A combined dehydration and heat illness protocol was developed. Urinary specific gravity limits of 1.022 for start of shift and 1.030 for end of shift were selected; workers exceeding these values were not allowed into the workplace (if the start of shift limit was exceeded) or were retested prior to their next working shift (if the end of shift limit was exceeded). A target of 1.015 as a euhydrated state for start of shift was adopted for workforce education. CONCLUSIONS: This study found that "involuntary dehydration" did not occur in well informed workers, which has implications for heat stress standards that do not make provision for full fluid replacement during heat exposure. Fluid replacement during meal breaks was not significantly increased above fluid replacement rates during work time, with implications for the duration and spacing of meal breaks on long shifts. Testing of urinary specific gravity was found to be a good indication of hydration status and a practical method of improving workforce awareness and understanding of this important risk factor. Approximately 10 000 dehydration tests have been conducted under the dehydration protocol in a workforce of 2000 persons exposed to thermal stress and has proved practical and reliable. (+info)
Does canopy position affect wood specific gravity in temperate forest trees?
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The radial increases in wood specific gravity known in many tree species have been interpreted as providing mechanical support in response to the stresses associated with wind loading. This interpretation leads to the hypothesis that individuals reaching the canopy should (1) be more likely to have radial increases in specific gravity and (2) exhibit greater increases than individuals in the subcanopy. Wood specific gravity was determined for three species of forest trees (Acer rubrum, Fagus grandifolia and Tsuga canadensis) growing in central Massachusetts, USA. Acer rubrum shows radial increases in specific gravity, but these increases are not more pronounced in canopy trees; the other two species show a pattern of radial decreases. The degree of radial increase or decrease is influenced by tree height and diameter. Of the dominant tree species for which we have data, A. rubrum, Betula papyrifera and Pinus strobus show radial increases in specific gravity, whereas F. grandifolia, T. canadensis and Quercus rubra show decreases. The occurrence of radial increases in B. papyrifera and P. strobus, which are often canopy emergents, suggests that it is overall adaptive strategy that is important rather than position (canopy vs. subcanopy) of any individual tree. It is suggested that radial increases in specific gravity are associated with early-successional status or characteristics and decreases with late-successional status or persistence in mature forest. (+info)
Evaluation of urine specimen integrity in a public health STD screening program.
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Detection of Chlamydia trachomatis and/or Neisseria gonorrhoeae infection in urine using molecular amplification assays has permitted institutions with limited medical facilities to offer testing for these sexually transmitted diseases (STDs). The Nebraska Public Health Laboratory (NPHL) investigated the validity of urine samples submitted for C trachomatis and/or N gonorrhoeae amplification after receiving a substantial number of clear specimens. Approximately 75% of all urine specimens submitted for STD testing to the NPHL were from correctional facilities. The falsification of urine specimens submitted for microbiology studies is not evaluated routinely, and this problem was previously undocumented. By using the criteria for specific gravity of 1.001 or less and a creatinine concentration of less than 5 mg/dL (442 mumol/L), approximately 8% of all specimens submitted during the study interval were determined to be inconsistent with urine. The microbiology laboratory should be aware of the possibility for specimen manipulation to identify facilities submitting falsified specimens, to initiate appropriate intervention, and to minimize false-negative reporting. (+info)
N-nitrosoproline excretion by rural Nebraskans drinking water of varied nitrate content.
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The N-nitrosoproline (NPRO) test for in vivo nitrosation was applied in a study of 44 rural Nebraska men drinking high- or low-nitrate water from private wells. The subjects followed diets low in NPRO and nitrate for 5 days. On days 4 and 5 they avoided ascorbate-rich foods. Urine was collected for 24 h on day 4 while the subjects followed normal activities and on day 5 after an overnight fast and taking 500 mg L-proline. We determined NPRO, nitrate, creatinine, and specific gravity in the urines, and nitrite and nitrate in single saliva specimens collected on days 4 and 5. Results for all variables were separated into those above and below the median values and were analyzed by univariate and multivariate consideration of the contingency tables. Nitrate concentration in drinking water (> or = or < 10 ppm nitrate-nitrogen) was significantly associated with both day 4 and day 5 NPRO (> or = or < 1.5 micrograms/day; P < 0.04); and with urine nitrate (> or = or < 1.5 mmol/day), saliva nitrite (> or = or < 5 mg/liter), and saliva nitrate (> or = or < 25 mg/liter) (P < or = 0.002). Urine nitrate was significantly (P < or = 0.03) associated with both day 4 and day 5 NPRO, with odds ratios of 4.2 and 5.4, respectively. Creatinine was positively associated with NPRO on day 4 (P = 0.04). These findings, like those of a recent study in Denmark, showed an association between nitrate intake in water and NPRO formation. Their significance for people drinking high-nitrate water remains to be determined. (+info)
Composition and digestive tract retention time of ruminal particles with functional specific gravity greater or less than 1.02.
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The objective of this study was to determine composition, particle size distribution, and in vivo kinetics of ruminal particles having functional specific gravity (FSG) greater or less than FSG of particles found in the omasum and reticulum of lactating dairy cows. Particles from the reticulum and the omasal had FSG of 1.03 and 1.02, respectively. Particles from ruminal contents with FSG higher (HP) or lower (LP) than 1.02 were isolated and labeled with Er or Dy, respectively. Four ruminally cannulated, lactating Ayrshire dairy cows were fed all-grass silage (AS) or 54% grass silage:46% concentrate (SC) diets in a cross-over design trial and used to study chemical composition and ruminal and total tract kinetics of HP and LP. Labeled particles were pulse dosed into the rumen of the cows and disappearance of the markers from ruminal HP and LP pools and excretion in feces was monitored for 72 and 120 h, respectively. Fecal marker excretion data were fitted using two-compartment mathematical age-dependent/age-independent (Gn-->G1) models. Inclusion of concentrate in the diet (SC) increased (P < 0.05) apparent total tract digestibility of dietary DM, OM and N. Digestibility of fiber fractions, NDF and ADF, was lower (P < 0.01 and P < 0.05, respectively) for SC compared with AS. The heavy particles had higher (P < 0.01) indigestible NDF and lower (P < 0.01) N concentration than LP. Particles from the HP pool passed from the rumen more rapidly (P < 0.01) than particles from LP (0.044 and 0.019 h(-1), respectively). Diet had no effect on particle rate of disappearance or pool size in the rumen. Across diets, pool size of LP was consistently larger (P < 0.05) than that of HP. Diet had no effect on total tract mean retention time (MRT) of LP or HP. Total tract MRT of LP was greater (P < 0.05) than MRT of HP (59.6 vs. 49.0 h, respectively). Results from this study support the hypothesis that functional specific gravity is an important factor determining the rate of outflow and residence time of feed particles within the reticulo-rumen and total digestive tract. Our data indicate that digesta particles with functional specific gravity greater or less than 1.02 have different composition and flow characteristics. Heavier particles contain more indigestible fiber and less N and are likely depleted of substrate available for microbial fermentation, are smaller in size, and have a higher passage rate/shorter retention time in the digestive tract than lighter particles. (+info)
Kinetics of hydration and effect of liquid uptake on specific gravity of small hay and silage particles.
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Kinetics of hydration of ground hay and silage particles (2-mm screen), determined by a pycnometric technique, was best described by a two- and one-pool exponential model, respectively. Fractional rates of hydration of the large pool, detected in hay particles only, and of the small pool present in both hay and silage particles averaged .135 and .021 min-1, respectively. When hydration was complete, liquid associated with particles averaged 1.16, 1.90, and .83 g/g of insoluble DM for bromegrass hay, alfalfa hay, and alfalfa silage, respectively. Functional specific gravity, which accounts for the effect of associated gas volume, averaged 1.54, 1.46, and 1.54, but unit specific gravity, calculated to include the effect of gases and liquid of hydration, averaged 1.22, 1.14, and 1.26 for bromegrass hay, alfalfa hay, and alfalfa silage, respectively. Preservation of forage as silage not only lowered gas volume, but also reduced water-holding capacity, both of which contribute to greater unit specific gravity and faster rate of escape from the rumen. In addition, estimates of unit specific gravity of approximately 1.2 indicate that even in the absence of associated gas, hydrated forage particles would tend to escape the rumen at a slower rate than that achieved by more dense particles. (+info)