Most dipsticks used in this study are likely to show a false positive test result in urines with high specific gravity, urines of alkaline with pH ≥ 8.0, and or urines contaminated with quaternary ammonium salt or antiseptic such as a chlorhexidine, and a false negative result in acidic urines with pH ≤3.0 according to manufacturer's instructions.
Specific gravity of urine samples was measured with a refractometer and urine chemical examination was measured by dipstick tests (Combur10 Test, Roche Diagnostics Indianapolis, IN, USA).
We measured specific gravity of urine samples to account for the variability of metal excretion associated with spot urine samples (Mason and Calder 1994).
Specific gravity of urine was measured using a handheld refractometer in each thawed aliquot before shipment to the CDC, except for 11 urine samples that had specific gravity measured using an Atago PAL-10S refractometer (Atago, Bellevue, WA, USA) at the CDC.
The specific gravity of urine may vary between 1.001 and 1.04 but is usually 1.01 1.025.
Adjusting for the specific gravity of urine was not useful because it is so highly correlated with urinary creatinine.
We have adjusted for specific gravity and urine dilution as time-varying covariates in our regression models to be consistent with our previously published studies.
The average specific gravity of urine from diabetic individuals was significantly higher than in nondiabetic individuals, but the difference between the two groups in the sum of As species in urine adjusted for specific gravity was not statistically significant.
To compensate for dilution, we measured specific gravity of urine using a digital refractometer (EUROMEX RD 712 clinical refractometer; EUROMEX, Arnhem, the Netherlands), and adjusted measured analyte concentrations to the mean specific gravity of all samples (1.020 g/mL).
The specific gravity of urine ranged from 1.002 to 1.037 in spot samples of 534 subjects (aged 18 68) with a high correlation (r = 0.82, p <.001) observed between creatinine and specific gravity (Carrieri et al., 2000).
