Reference limits for copper and iron in liver biopsies.

Using 141 liver biopsy results (103 adults, 38 children) and a rank-order approach, the following reference limits were found: copper 55 microg/g dry weight, iron 1800 microg/g dry weight (adults only), and iron index 1.0. The study was made feasible by the fact that both copper and iron were measured as standard practice in every liver biopsy received for either test. The added analyte tended to contribute more to normal results. Specimens with elevations of both were infrequent (7 of 141) and significant elevations of both (copper >200 microg/g, iron index >2.0) were suggestive of contamination. Advantages of using patient data included studying specimens of limited availability and acquiring information on the distribution of elevated results seen in clinical practice. Disadvantages included increased uncertainty in the reference limits relative to a normal population. Although most of the study population consisted of patients referred for diagnosis of Wilson's disease or hemochromatosis, the reference intervals were similar to those reported from autopsy studies.