Soft Tissue

Biopsy specimens of soft tissues, particularly liver, are useful for assessing the body burden of some elements. Reference intervals for soft tissues have been established for many elements using autopsy specimens obtained from accident victims (16-18). Much of the knowledge regarding toxic element accumulation and elimination kinetics has been learned from these studies. For example, accumulation of cadmium is higher in smokers than in non-smokers and, due to the slow elimination kinetics, increases with age. Age-related accumulation is also recognized for mercury and iron.

Chronic iron overload is routinely evaluated with liver biopsy specimens, particularly to support the diagnosis of hemochromatosis. However, multiple specimens may be required as distribution of iron is not homogenous (19). Tissue quality should be verified histologically to ensure the quality of the hepatic tissue that is analyzed, and results should be expressed based on age of the patient. The hepatic iron index (^mol iron per year of life, per mg of tissue) is quite useful for distinguishing iron accumulation due to hemochromatosis from that which occurs with age or mild liver disease, such as is observed with chronic alcohol use and hepatitis (20).

Like other specimens collected for elemental analysis, procedures followed for collection of soft tissue should be sensitive to sources of external contamination. Blocked tissue should not be stained prior to quantitative elemental analysis because many histological stains and reagents contain toxic elements that could contribute to falsely elevated results. The preferred specimen is a fresh needle biopsy core submitted to the laboratory in a trace metal-free tube, without any transport media or preservatives. Because these specimens are typically dried prior to analysis (to obtain a dry weight for which results can be expressed), transport media is not necessary. In fact, storing liver biopsy tissue in saline was shown to generate falsely low iron results because the unbound forms of the iron diffuse from the tissue into the saline. However, concentrations of many elements in paraffin-embedded and formalin-fixed tissue are comparable to fresh tissue (6,21,22).

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