The New York State Department of Health’s Wadsworth Center operates a proficiency testing (PT) program for clinical laboratories analyzing body fluids (blood, urine and serum) for trace elements. The PT program is approved in the US by the Centers for Medicaid and Medicare Services under CLIA 88, and participation is mandatory for all laboratories analyzing specimens originating from New York State. The blood lead PT component has been in operation for more than 30 years, and consists of circulating whole blood obtained from lead-dosed goats to ~100 laboratories located throughout the US, along with several overseas reference laboratories. The use of blood from lead-dosed goats is necessary because methods based on electrochemistry (e.g., ASV) require protein-bound Pb to be “released” or de-complexed prior to the determination.
In 2001, the PT program was expanded to include additional toxic elements (Hg, Cd and As), along with a urine panel (Pb, Cd, Hg and As) and a serum panel (Cu, Zn, Se and Al). Each panel consists of 5 samples and are distributed 3 times a year for a total of 15 samples per matrix. PT data returned by participants are evaluated using quality specifications that are based on a consensus reached by several trace element PT schemes from Europe and North America. The PT scheme organizers have formed a Network that seeks to harmonize PT requirements across multiple schemes and explore the use of common samples. Details about the cooperative network are available online (http://www.occupational-environmental-laboratory.com/) and in the peer-reviewed literature (1, 2).
The experience of the New York State PT program has been that some trace elements are more difficult to determine than others. For example, the determination of mercury in urine is quite challenging, from the perspective of both the PT provider and the testing laboratory. Yet measurements of mercury in whole blood are among the most successful. Comparisons between clinical methods based on inorganic mass spectrometry (e.g., ICP-MS) and those based on atomic absorption spectrometry show how performance depends on the quality of the specific laboratory rather than on the specific technique used. An evaluation of the NY PT program for whole blood trace elements was conducted by circulating NIST SRM 955c Lead in Caprine Blood as a PT sample prior to its release by NIST. Target values were assigned using a selection of reference laboratories, as well as by using robust statistics. A comparison between the program target values and the certified values provided by NIST for blood lead reveal some potential bias among blood lead testing laboratories.
1. Taylor A, Angerer J, Arnaud J, et al. Occupational and environmental laboratory medicine: A network of EQAS organisers. Accreditation and Quality Assurance. 2006;11:435-439.
2. Arnaud J, Jones R, LeBlanc A, et al. Criteria to define the standard deviation for proficiency assessment for the determination of essential trace elements in serum: comparison of Z-scores based on the Horwitz function or on biological variability. Accreditation and Quality Assurance. 2009;14:427-430. |
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