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Evaluation of filter paper blood lead methods: results of a pilot proficiency testing program
N V Stanton1, J M Maney, R Jones
1Wisconsin State Laboratory of Hygiene, Toxicology Section, 2601 Agriculture Dr., P.O. Box 7996, Madison, WI 53707-7996, USA. nvstox@mail.slh.wisc.edu
Background:
Lead testing on dried filter paper (FP) blood spots is used routinely by some laboratories for lead poisoning screening. Proficiency testing (PT) as required under CLIA '88 laboratory regulations has not been available for these methods.
Methods:
We describe a suitable PT scheme and evaluate FP laboratory performance based on program results. Monthly testing events consisting of five FP specimens were provided to six participating laboratories. Results were evaluated against target values determined by referee laboratories.
Results:
Preliminary FP laboratory results showed poor agreement with specimen target values, exhibiting a mean absolute bias of 0.29 micromol/L (5.9 microg/dL). Five of six participating laboratories demonstrated significant improvement in later testing events, with bias decreasing to 0.12 micromol/L (2.5 microg/dL). Performance varied widely between the participating laboratories and appeared to be method dependent. When evaluated using CLIA blood lead acceptability criteria, the proportion of acceptable individual specimen results (n = 35) ranged from 54% to 100%. On a testing event basis (n = 7), the proportion of acceptable events ranged from 29% to 100%.
Conclusions:
A suitable FP PT program now exists to capably assist and monitor FP laboratories. Based on overt PT results, properly utilized FP testing methods can accurately measure blood lead concentration.