Specific gravity adjustment of urine analysis results

Analysis of urine samples for compounds such as lead, phenol, or 4,4'-methylene bis (2-chloroaniline) (MBOCA) are often adjusted for specific gravity following a recommendation in a NIOSH Benzene Criteria Document. The adjustment normalizes all results to a specific gravity of 1.024 by multiplying the analytical result in microgram/liter by 24/G where G is the last 2 digits of the specific gravity of the urine sample. The adjustment calculation is based on a suggestion by Levine and Fahy, who found that the urine solids content is roughly proportional to 24/G. We believe this adjustment to be inappropriate based on the following considerations.