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Chromium (Cr) has an atomic mass of 51.996, atomic number 24, and valences ranging from 2(-) to 6(+). Hexavalent chromium, Cr(+6), and trivalent chromium, Cr(+3), are the 2 most prevalent forms. Cr(+3) is the only oxidation state present under normal physiologic conditions. Cr(+6) is widely used in industry to make chromium alloys including stainless steel pigments and electroplated coatings. Cr(+6), a known carcinogen, is rapidly metabolized to Cr(+3). Cr(+3) is the only form present in human urine.
Screening for occupational exposure
The National Institute for Occupational Safety and Health (NIOSH) draft document on occupational exposure reviews the data supporting use of urine to assess chromium exposure.(1) They recommend a Biological Exposure Index of 10 mcg/g creatinine and 30 mcg/g creatinine for the increase in urinary chromium concentrations during a work shift and at the end of shift at the end of the workweek, respectively (Section 3.3.1).
Normal specimens have extremely low levels of creatinine; elevated results could easily be a result of external contamination. Precautions must be taken to ensure the specimen is not contaminated. Metal-free urine collection procedures must be followed. Refrigeration is preferred over chemical methods of preservation.
High concentrations of gadolinium and iodine are known to interfere with most metals tests. If either gadolinium or iodine-containing contrast media has been administered, a specimen should not be collected for 96 hours.
Chromium/creatinine ratio: <10.0 mcg/g creatinine
Centers for Disease Control and Prevention: NIOSH Draft Criteria Document Update: Occupational Exposure to Hexavalent Chromium September 2008. DRAFT-Criteria-Document-Update-Occupational-Exposure-to-Hexavalent-Chromium. Retrieved 2/27/09. Available at http://www.cdc.gov/niosh/review/public/144/