Evaluating selenium poisoning.

Selenium poisoning in humans is reviewed from the perspective of the clinical laboratory. While evaluation of selenium poisoning is straightforward when the analytic results are markedly elevated and the patient is acutely symptomatic, distinguishing toxic from non-toxic elevations is a more frequent issue and more challenging. A significant problem is that selenium is determined as its total concentration in spite of the fact that different chemical forms of selenium have different toxic potentials. In the published reports reviewed herein, serum selenium concentrations span the following ranges: 400-30,000 micro g/L associated with acute toxicity, 500-1400 micro g/L associated with chronic toxicity, and <1400 micro g/L free of toxicity; the category is determined by signs and symptoms in the patient. Most reports that describe acute selenium poisoning involve ingestion of inorganic compounds such as selenious acid, found in gun-bluing agents, and fatalities that occur within the first day are associated with postmortem blood selenium levels >1400 micro g/L. Tissue selenium levels show a complex pattern and significant elevations in organs such as kidney are not always indicative of toxicity. As with many trace elements, measuring selenium concentrations in body fluids and tissues tends to be easier than understanding what the results mean.

Interpreting hair mercury levels in individual patients.

Evaluation of mercury exposure in an individual patient ideally includes the presenting history, physical examination, consideration of the differential diagnosis, and mercury analysis of blood and urine specimens. Analysis of mercury in hair specimens may supply useful supplemental information about exposure to organic compounds such as methylmercury, particularly to help reconstruct the pattern of prior exposure. The most appropriate specimen is generally terminal-type hair from the occipital-neck junction, clamped to maintain strand alignment, and oriented to the scalp. Hair from the initial 0.5 cm adjacent to the scalp represents on average 1-3 wk before collection, and consideration of the time frame represented by the specimen is an important part of the evaluation. Literature reports describe hair mercury levels as high as 2400 microg/g. Hair mercury level is usually <1 microg/g in individuals who do not eat fish but may be >30 microg/g in those who frequently consume fish with high mercury content. Hair mercury level is often not correlated with blood mercury concentration or symptoms of mercury toxicity, and reports of hair contamination by exogenous mercury are not uncommon. Hair mercury level is notoriously prone to misinterpretation and should be used with an understanding of its limitations.

Interpreting mercury in blood and urine of individual patients.

The effects of mercury exposure are determined by: (a) chemical form, (b) route of exposure, (c) dose, and (d) patient factors. Patient factors include age, genetics, environmental aspects, and nutritional status, and are responsible for different individual responses to similar doses. When blood and urine are collected to evaluate exposure, the results are influenced by (a) specimen collection, (b) analysis, and (c) the time elapsed from exposure. Interpretation is influenced by the patient's symptoms and is facilitated by comparison to published reports. The ranges reported in the literature are broad, with elevations as high as 16,000 microg/L in blood and 11,000 microg/L in urine. Interpretation is relatively straightforward when the results are massively elevated, but becomes increasingly difficult as concentrations approach the population norms (blood and urine mercury < 10-20 microg/L). Interpretation can be aided by biological markers (eg, urine porphyrins, beta2-microglobulin, and N-acetyl-beta-D-glucosaminidase).

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.