When obtaining biologic specimens for chromium analysis, care must be taken to avoid sample contamination and chromium loss during collection, transportation, and storage. For example, use of stainless steel utensils to collect tissue samples might raise tissue chromium levels, as will stainless steel grinding and homogenizing equipment. Some plastic containers contain significant amounts of leachable chromium; therefore, specially prepared acid-washed containers should be obtained from the laboratory.
Considerable care also must be taken in the analysis to minimize chromium volatilization during sample washing [EPA 1984a].
Blood or Serum Chromium Levels
Several methods are available for the analysis of chromium in different biological media [ATSDR 2000]. For example, Cr(VI) and complexes of Cr(III) can be rapidly determined in plasma and other biological specimens via a high performance anion-exchange liquid chromatograph technique [Suzuki 1987].
Blood distribution of chromium appears to be divided evenly between plasma and erythrocytes. In the absence of known exposure, whole blood chromium concentrations are in the range of 2.0 µg/100 mL to 3.0 µg/100 mL; lower levels occur in rural areas, and higher levels occur in large urban centers.
As we have discussed in the previous section on the biologic fate of chromium, Cr(VI) enters red blood cells, but Cr(III) does not. Therefore, it is possible to distinguish sources and types of exposure (Cr(VI) versus other forms of Cr) by measuring RBC versus serum Cr. This can be especially helpful if urine Cr levels are elevated and one wants to know if this indicates a toxic (e.g., Cr[VI]) exposure or an essentially benign (e.g., Cr[III]) exposure.
Values above background levels are considered potentially toxic, but levels have not been correlated with specific physiologic effects. Chromium rapidly clears from the blood, and measurements relate only to recent exposure.
Urinary Chromium Levels
Wide individual variation in metabolism and rapid depletion of body burden limit the value of urinary chromium monitoring.
Urinary chromium excretion reflects absorption over the previous 1 or 2 days only.
In occupational settings, a urinary chromium concentration of 40 µg/L to 50 µg/L, immediately after a work shift reflects exposure to air levels of 50 µg/m³ of soluble Cr(VI) compounds, a concentration associated with nasal perforations in some studies. If sufficient time has elapsed for urinary clearance, a negative bio-monitoring result can occur even with injurious past exposure.
Assuming no source of excessive exposure, urinary chromium values are typically less than 10 µg/L for a 24-hour period [ATSDR 2000].
Urinary β2-Microglobulins Levels
Urinary β2-microglobulins were significantly higher in chromeplaters exposed to Cr(VI) than in unexposed controls [Lindberg and Vesterberg 1983].
Hair or nail analysis is of little use in evaluating an individual patient because it is impossible to distinguish chromium bound within the hair during protein synthesis from chromium deposited on the hair from dust, water, or other external sources. Populations with no known chromium exposure reportedly have hair levels ranging from 50 parts per million (ppm) to 100 ppm chromium.
The presence of chromium and chromium complexes in biologic complexes can be determined using chromatographic and colorimetric techniques; patch testing and lymphocyte proliferation testing have been used to determine chromium sensitivity [ATSDR 2000; Meditext 2005]. |
