Comparison of interlaboratory results for blood lead with results from a definitive method

Results reported by 113 participants in the Blood Lead Proficiency Testing Program conducted by the Center for Disease Control were compared with those obtained by the National Bureau of Standards (NBS) with a definitive methods (mass spectroscopy-isotopic dilution) for blood lead analyses. Data were compiled from the results obtained for 12 whole-blood samples containing 1.5 g of disodium EDTA per liter. Twelve separate blood samples were obtained from cattle which had been given lead nitrate orally. Lead concentrations in the samples ranged from 0.628 to 4.93 mumol/L (130-1020 micrograms/L) as determined by NBS. The methods used by laboratories were classified according to six basic groups: anodic stripping voltametry; and atomic absorption spectroscopy in which either extraction, carbon rod, graphite furnace, tantalum strip, or Delves cup was used. For results obtained in each group a linear regression analyses of laboratory values was made on the basis of NBS values. In comparison to the definitive method, most field methods for blood lead tended to overestimate the lead concentration when the actual lead concentration was less than 1.96 mumol/L (400 micrograms/L) and to underestimate the lead concentration when the actual lead concentration was greater than 2.45 mumol/L (500 micrograms/L).