External quality assessment schemes for inorganic elements in the clinical laboratory: Lessons from the OELM scheme.

Measurements of inorganic elements in clinical laboratories produce results used for the diagnosis, the treatment and the monitoring of deficiencies or overloads. The main objective of External Quality Assessment Schemes is to verify, on a regular frequency, that clinical laboratory results correspond to the quality requirement for patient care. Therefore, External Quality Assessment Schemes represent an essential component of a laboratory's quality management system. However, External Quality Assessment Schemes within the same analytical field remain heterogeneous for different reasons such as samples, determination of assigned value, acceptable limits, content of the reports. The aim of this review was to describe and illustrate some major critical aspects of External Quality Assessment Schemes based on Occupational and Environmental Laboratory Medicine external quality assessment scheme experience.

Biological monitoring of Italian soldiers deployed in Iraq. Results of the SIGNUM project.

BACKGROUND: Leukemia/lymphoma cases reported in 2001 among United Nation soldiers or peacekeepers deployed to the Balkans aroused alert on the exposure to depleted uranium. Recent epidemiological studies carried out in different European countries among peacekeepers who served in the Balkans failed to demonstrate a higher than expected risk of all cancers but, mostly due to their limitations in size and follow up time, leave open the debate on health risk of depleted uranium. The aim of SIGNUM (Study of the Genotoxic Impact in Military Units) was to identify potential genotoxic risk associated with the exposure to depleted uranium or other pollutants in the Italian Army military personnel deployed in Iraq. METHODS: Blood and urine samples were collected before and after the deployment from 981 Italian soldiers operating in Iraq in 2004-2005. As, Cd, Mo, Ni, Pb, U, V, W, and Zr were determined in urine and serum. DNA-adducts, 8-hydroxy-2'-deoxyguanine and micronuclei frequency were evaluated in blood lymphocytes. Three different genetic polymorphisms, GSTM1, XRCC1, OGG1 were analyzed. RESULTS: Significant T0-T1 reduction in the total concentration of uranium, increases for Cd, Mo, Ni, Zr, and decreases for As, Pb, W, and V in urine and plasma were observed. Increases in oxidative alterations and in micronuclei frequency, included in the range of values of non-occupationally exposed populations, were observed at the end of the period of employment. CONCLUSIONS: Our results did not detect any toxicologically relevant variation of DNA-damage biomarkers related to the deployment in the operational theater.

Evaluation of uncertainty of measurement from method validation data: an application to the simultaneous determination of retinol and alpha-tocopherol in human serum by HPLC.

An isocratic RP-HPLC method for the determination of retinol and alpha-tocopherol in serum, with fluorescence and UV/VIS detection, respectively, was developed and validated according to international guidelines. Detection (retinol 0.015 mg/L, alpha-tocopherol 0.29 mg/L) and quantification (retinol 0.05 mg/L, alpha-tocopherol 0.95 mg/L) limits were determined. Repeatability was <3.3% and <2.9% and intermediate precision was <4.6% and <3.2%, for retinol and alpha-tocopherol, respectively. Certified reference materials were utilised to assess bias and guarantee traceability to SI units. Expanded uncertainties (retinol 8.9%; alpha-tocopherol 7.9%), estimated according to the EURACHEM/CITAC guide from method validation data, satisfied fit-for-purpose requirements based on biological variability.

Quality specifications for the determination of copper, zinc, and selenium in human serum or plasma: evaluation of an approach based on biological and analytical variation.

BACKGROUND: Trace element external quality assessment schemes monitor laboratory performance and provide a stimulus for improvement in accuracy. However, monitoring of participant performance varies according to the scheme and can lead to conflicting conclusions. METHODS: Quality specifications based on biological intra- and interindividual variability were calculated and compared to those currently used by various trace element external quality assessment schemes for plasma or serum copper, zinc, and selenium concentrations. For this purpose, we evaluated results reported by participating laboratories in different schemes, at key concentrations, using z scores. RESULTS: Minimal quality specifications developed from the biological intra- and interindividual variability were, for Cu, +/-0.84 micromol/L or 12% of the assigned target concentration, whichever is greater; for Zn, +/-1.20 micromol/L or 15% of the assigned target concentration, whichever is greater; and for Se, +/-0.072 micromol/L or 12% of the assigned target concentration, whichever is greater. Reported performance of the participating laboratories depended on analyte, concentration, and the selected quality specification. In addition, the most commonly used methods for the determination of Cu, Zn, and Se may give different results. CONCLUSIONS: The proposed minimal quality specifications based on biological variation are generally slightly less stringent than those currently in use, although they do not drastically change the performance evaluation in the different schemes. These specifications are a first step in the harmonization of practices among the schemes and remain to be evaluated.

An international comparability study to determine the sources of uncertainty associated with a non-competitive sandwich fluorescent ELISA.

BACKGROUND: Immunoassays allow the specific detection and quantitation of biological molecules in complex samples at physiologically relevant concentrations. However, there are concerns over the comparability of such techniques when the same assay is performed by different operators or laboratories. An international intercomparison study was performed to assess the uncertainty involved in the estimation of a protein cytokine concentration using a fluorescent ELISA. METHODS: The intercomparison study method was based on a non-competitive sandwich immunoassay with an enhancement step to generate a fluorescent readout. The intercomparison was performed in two phases, with the uncertainty of the instrument determined separately from that of the assay. The 11 laboratories participating in the study represented national metrology institutes or nominated expert laboratories. RESULTS: Participants were asked to determine an undisclosed concentration of interferon using a supplied standard. The mean participant estimate and experimental standard deviation of the mean was 3.54+/-0.22 mg/L, with the spread of data ranging around +/-35% of the mean. The quantitation range of the ELISA and of participants' instruments displayed large variation that contributed to the overall uncertainty. CONCLUSIONS: Identified sources of uncertainty within the ELISA methodology included pipetting, data fitting, model selection and instrument/plate variation.

Differences in national legislation for the implementation of lead regulations included in the European directive for the protection of the health and safety of workers with occupational exposure to chemical agents (98/24/EC).

BACKGROUND: The European Council Directive 98/24 on the protection of the health and safety of workers exposed to chemical agents sets out provisions for environmental and biological monitoring, making specific reference to binding limit values and health surveillance measures for those with exposure to lead OBJECTIVES: To compare how the Directive has been implemented at a national level in EU countries and to determine whether workers receive equivalent protection. METHODS: Information on selected key issues was collected from 14 EU countries by means of a structured questionnaire. RESULTS: National occupational exposure limit values generally reflect that set by the Directive (0.15 mg/m(3)), but in five cases lower limits are set. National binding biological limit values range from 20 microg/100 ml blood in one country up to 80 microg/100 ml blood in others. The risk to the unborn child is generally recognised with specific measures for women of child-bearing potential or those that are pregnant or breast feeding. In only three countries are special arrangements included for young workers. Limits at which medical surveillance is put into effect are more consistent at 40 microg/100 ml in most countries. The Directive also refers to guidelines for health surveillance but none have been issued with respect to lead. Thus monitoring strategies and requirements for analytical performance vary considerably. CONCLUSIONS: The results of this survey suggest that protection of workers against the risk of exposure to lead at work is far from uniform across the European Union. Such disparity may also have implications on the requirements set at national level for laboratories measuring lead in blood and/or air. In the interest of harmonisation within the EU, further consideration should be given to the Annex II of the EC Directive 98/24, taking into account the suggestions for lower binding limit values for lead; this should include full guidelines for medical surveillance and requirements for laboratories should be issued.

Estimate of uncertainty of measurement from a single-laboratory validation study: application to the determination of lead in blood.

BACKGROUND: Lead is an environmental pollutant, and human exposure is assessed by monitoring lead concentrations in blood. Because the main source of environmental exposure has been the use of leaded gasoline, its phase-out has led to decreased lead concentrations in the general population. Therefore, validated analytical methods for the determination of lower lead concentrations in blood (<150 microg/L) are needed. In addition, new ISO standards require that laboratories determine and specify the uncertainty of their results. METHODS: We validated a method to determine lead in blood at concentrations up to 150 microg/L by electrothermal atomic absorption spectrometry with Zeeman background correction according to EURACHEM guidelines. Blood samples were diluted (1:1 by volume) with 2 mL/L Triton X-100. NH4H2PO4 (5 g/L) and Mg(NO3)2 (0.5 g/L) were used as modifiers. Matrix-matched standards were used for calibration. RESULTS: We determined the limits of detection (3.1 microg/L) and quantification (9.4 microg/L). Repeatability and intermediate imprecision within the range 35-150 microg/L were <5.5% and <6.0%, respectively. We assessed trueness by use of certified reference materials, by recovery tests, and by comparison with target values of other reference materials (candidate external quality assessment samples). The expanded uncertainty ranged from 20% to 16% (with a confidence level of 95%) depending on concentration. CONCLUSIONS: This study provides a working example of the estimate of uncertainty from method performance data according to the EURACHEM/CITAC guidelines. The estimated uncertainty is compatible with quality specifications for the analysis of lead in blood adopted in the US and the European Union.

Comparison of procedures for evaluating laboratory performance in external quality assessment schemes for lead in blood and aluminum in serum demonstrates the need for common quality specifications.

BACKGROUND: The different scoring methods used by eight European External Quality Assessment Schemes (EQASs) for occupational and environmental laboratory medicine were compared to develop suitable quality specifications as a step toward harmonization. METHODS: Real results for blood lead and serum aluminum assays, reported by participants in Italian and United Kingdom EQASs, were evaluated according to individual scheme scoring criteria. The same results were then used to produce z scores using scheme-based between-laboratory SDs as the estimate of variability to determine whether simple performance-derived quality specifications produced better agreement among schemes. RESULTS: The schemes gave conflicting assessments of participants' performance, and participants judged to be successful by one scheme could be defined as performing inadequately by another. An approach proposed by Kenny et al. (Scand J Clin Lab Invest 1999;59:585), which uses clinical inputs to set targets for analytical imprecision, bias, and total error allowable, was then used to elaborate quality specifications. CONCLUSIONS: We suggest that the CLIA '88 recommendations for blood lead (+/- 40 micro g/L or +/- 10% of the target concentration, whichever is the greater) could be used as a quality specification, although a revision to +/- 30 micro g/L or +/- 10% is recommended. For serum aluminum, a suitable quality specification of +/- 5 micro g/L or +/- 20% of the target concentration, whichever is the greater, is suggested. These specifications may be used to compare laboratory performance across schemes.

Age dependence of potentially toxic elements (Sb, Cd, Pb, Ag) in human liver tissue from paediatric subjects.

Toxic elements are present at low concentrations in the environment. This work was undertaken to investigate the age dependence of the liver content of selected elements in paediatric populations, as an index of internal exposure. Liver samples were collected at autopsy from 157 subjects, aged < 1 day to 6 years, as part of investigations on a possible role of Sb compounds in sudden infant death syndrome (SIDS). In addition to Sb, the concentrations of Ag, Cd and Pb were also determined by inductively coupled plasma mass spectrometry on the remaining digest. Comparison of 95% confidence intervals of the median concentrations of the four elements suggested that there were no differences between the two categories of cause of death, SIDS or those who had died of an identified disease. Cadmium, lead and antimony median concentrations were lower than corresponding values observed in adult populations. Silver concentrations were significantly higher at birth and decreased with age. Cadmium levels were almost negligible in neonates and infants, but increased in older children. The finding of non-negligible concentrations of both Ag and Pb in neonatal liver provides further direct evidence that these elements cross the human placental barrier. The reported data, by far the largest collection observed in subjects less than 1 year old, are the result of exposure, during pregnancy and in early childhood, to present levels of these elements in the environment. They can serve as a reference to compare post-mortem values from individuals or groups of subjects in this age range when an exposure risk is suspected and to highlight trends in human exposure.