• Component Description
• Eligible Sample
• Description of Laboratory Methodology
• Data Processing and Editing
• Laboratory Quality Assurance and Monitoring
• Analytic Notes
• References
• Codebook
  • SEQN - Respondent sequence number
  • WTSSUG2Y - SSUSG_E 2 year weights
  • SSUSG - Urine specific gravity

National Health and Nutrition Examination Survey

2007-2008 Data Documentation, Codebook, and Frequencies

Urine Specific Gravity Measurement (Surplus) (SSUSG_E)

Data File: SSUSG_E.xpt

First Published: April 2011

Last Revised: April 2022

Component Description

Creatinine correction is the most commonly used method to compensate for variation in urine dilution when urinary biomarker is analyzed. However, in some case, Specific Gravity (SG), or the combination of SG and creatinine was found to be more appropriate. In this study, the potential value of using SG, and both SG and creatinine will be investigated. The primary goal was to find if a correlation exists between uncorrected, creatinine-corrected, SG-corrected, and both creatinine- and SG-corrected urinary NNAL and serum cotinine, and which value showed the strongest correlation. Another goal was to determine the best method of correcting NNAL to account for variability in interpersonal urine concentrations in NHANES samples using creatinine and SG as normalizing factors both independently and simultaneously.

Eligible Sample

The eligible samples are those that have adequate volume after NNAL assay. All participants aged 6 years and older from NHANES 2007-2008 were subjected to NNAL assay.

Description of Laboratory Methodology

SG will be measure by a digital hand-held refractometer ATAGO PAL-10S, with automatic temperature compensation. This refractometer has been validated before and has been used for other project. The measurement of urine SG is rather simple: place approximately 0.3 ml of well-mixed urine sample onto the prism surface and press the START key. The measurement will be displayed on the screen. The refractometer will be set to zero with HPLC water once for each run. Since there are 24 samples in each run, the refractometer will be auto-zeroed every 24 samples.

Data Processing and Editing

Data was received after all the SG measurements were complete. The data were not edited.

Laboratory Quality Assurance and Monitoring

One blank and one QC were measured in each run. All final reported data were from runs confirmed to be within statistical control limits using the multi-rule quality control system implemented in the Division of Laboratory Sciences, National Center for Environmental Health, CDC.

Analytic Notes

There is only one variable: SSUSG, specific gravity measured on the refractometer ATAGO PAL-10S. Specific gravity is the ratio of the density (mass of a unit volume) of a substance (urine) to the density (mass of the same unit volume) of a reference substance (water).

Subsample Weights

Sample weights are required to analyze these data properly. Specific sample weights for this subsample are included in this data file and should be used when analyzing these data. When observations were removed from this data file, a new sample weight was created and added to this data file (WTSSUG2Y). Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial for further details on the use of sample weights and other analytic issues.

References

• Heavner DL, Morgan WT, Sears SB, Richardson JD, Byrd GD, Ogden MW. Effect of creatinine and specific gravity normalization techniques on xenobiotic biomarkers in smokers' spot and 24-h urines. J Pharm Biomed Anal. 2006 Mar 3;40(4):928-42.
• Nermell B, Lindberg AL, Rahman M, Berglund M, Persson LA, El Arifeen S, Vahter M.
  Urinary arsenic concentration adjustment factors and malnutrition. Environ Res. 2008 Feb;106(2):212-8.
  
• Suwazono Y, Akesson A, Alfvén T, Järup L, Vahter M. Creatinine versus specific gravity-adjusted urinary cadmium concentrations. Biomarkers. 2005 Mar-Jun; 10(2-3):117-26.

Codebook and Frequencies