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Evaluation of Filter Paper Blood Lead Methods: Results of a Pilot Proficiency Testing Program

¹ Wisconsin State Laboratory of Hygiene, Toxicology Section, 2601 Agriculture Dr., P.O. Box 7996, Madison, WI 53707-7996.

² Centers for Disease Control and Prevention, National Center for Environ-mental Health, Environmental Health Lab Services, 4770 Buford Hwy., Atlanta, GA 30341.

³ Based in part on the data presented here, CDC has revised its position regarding the use of FP-based methods by CDC childhood lead poisoning grantees. This new position is described in a letter to those grantees dated February 25, 1999.
^a Author for correspondence. Fax 608-224-6259; e-mail nvstox{at}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 µmol/L (5.9 µg/dL). Five of six participating laboratories demonstrated significant improvement in later testing events, with bias decreasing to 0.12 µmol/L (2.5 µg/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.

The following articles in journals at HighWire Press have cited this article:

				K. Verebey, T. P. Moyer, D. E. Nixon, and O. K. Ash Filter Paper-collected Blood Lead Testing in Children The authors of the editorial cited above respond: Clin. Chem., July 1, 2000; 46(7): 1024 - 1028. [Full Text] [PDF]

				N. Stanton, J. Maney, and R. Jones More on Filter Paper Lead Testing Clin. Chem., July 1, 2000; 46(7): 1028 - 1029. [Full Text] [PDF]

				T. P. Moyer, D. N. Nixon, and K. O. Ash Filter Paper Lead Testing Clin. Chem., December 1, 1999; 45(12): 2055 - 2056. [Full Text] [PDF]