Specific gravity adjustment of urine analysis results

Area of Science:

• Occupational Health
• Toxicology
• Analytical Chemistry

Background:

• Urine analysis for toxic compounds like lead, phenol, and 4,4'-methylene bis (2-chloroaniline) (MBOCA) is common in occupational health.
• Current methods often adjust results based on urine specific gravity, following a NIOSH Benzene Criteria Document recommendation.

Purpose of the Study:

• To evaluate the appropriateness of the specific gravity adjustment method for urine analyte concentrations.
• To question the validity of the 24/G calculation for normalizing urine sample results.

Main Methods:

• Review of the scientific basis for specific gravity adjustment in urine analysis.
• Analysis of the relationship between urine solids content and specific gravity.
• Critique of the Levine and Fahy suggestion underpinning the adjustment method.

Main Results:

• The adjustment method, multiplying results by 24/G (where G is the last two digits of specific gravity), is based on a flawed premise.
• The assumption that urine solids content is proportional to 24/G is not adequately supported.
• This adjustment may lead to inaccurate exposure assessments for various chemical compounds.

Conclusions:

• The specific gravity adjustment for urine analytes is considered inappropriate.
• Re-evaluation of current biomonitoring practices for chemical exposures is recommended.
• Alternative methods for normalizing urine sample results should be explored.