Disparities in clinical laboratory performance for blood lead analysis
J. D. Sargent, L. Johnson and S. Roda
Department of Pediatrics, Dartmouth-Hitchcock Medical Center, Lebanon, NH, USA.
OBJECTIVE: To evaluate the validity of blood lead analysis for clinical
specimens. DESIGN: We submitted blood lead samples with a known lead
concentration, in a blinded fashion, as clinical specimens to 18
laboratories. These laboratories were surveyed for the following
characteristics that were hypothesized to be related to assay validity:
laboratory ownership (state vs private), participation in the Centers for
Disease Control Blood Lead Proficiency Program, assay method, and price.
Each laboratory received 6 specimens with an actual blood lead (ABPb)
concentration of 0.43 mumol/L (9 micrograms/dL) and 3 additional
specimens--each with an ABPb concentration of 0.33, 0.89, and 1.59 mumol/L
(6.9, 18.4, and 32.9 micrograms/dL, respectively). OUTCOME MEASURES:
Misclassification error rates for reporting an elevation ( > or = 0.48
mumol/L [ > or = 10 micrograms/dL) in the blood lead concentration, the
within-laboratory mean and coefficient of variation (CV) (for multiple
specimens with an ABPb concentration of 0.43 mumol/L [9 micrograms/dL]),
and the adjusted odds of a reported blood lead concentration differing from
those of an ABPb concentration by more than 0.14 mumol/L (3 micrograms/dL).
RESULTS: Blood lead results were obtained for 157 of 162 submissions. One
laboratory reported all blood lead specimens as "below 0.48 mumol/L (10
micrograms/dL)." Two (11%) of 18 specimens with an ABPb concentration of
0.89 mumol/L (18.4 micrograms/dL) and 1 (6%) of 17 with an ABPb
concentration of 1.59 mumol/L (32.9 micrograms/dL) were classified as below
0.48 mumol/L (10 micrograms/dL); 2 (11%) of 18 with an ABPb concentration
of 0.33 mumol/L (6.9 micrograms/dL) and 44 (42%) of 104 with an ABPb
concentration of 0.43 mumol/L (9 micrograms/dL) were classified as 0.48
mumol/L or greater ( > or = 10 micrograms/dL). For specimens with an
ABPb concentration of 0.43 mumol/L (9 micrograms/dL), the within-laboratory
mean ranged from 0.23 to 0.52 mumol/L (4.8-10.7 micrograms/dL); the CV
ranged from 3% to 37%. Laboratories that used anodic stripping voltammetry
were 6.3 (95% confidence interval, 1.4-28.6) times more likely to report a
specimen that differed from the ABPb concentration by more than 0.14
mumol/L (3 micrograms/dL) than those that used atomic absorption methods.
No other laboratory characteristic predicted discordance between the
reported blood lead and ABPb concentrations. CONCLUSIONS: This study
documents wide variation in the validity of the blood lead measurement
among clinical laboratories. While the performance of some laboratories far
exceeded the criteria of the Centers for Disease Control Blood Lead
Proficiency Program, others made large errors that could have resulted in
the false-negative misclassification of children with significant lead
exposure. Given these differences, the purchasers of laboratory services
may require access to laboratory proficiency data to make rational choices
among clinical laboratories. Further study of laboratory performance on
clinical specimens is required to determine if order-of-magnitude errors
occur with sufficient frequency to warrant routine submission of blinded
quality control specimens by proficiency programs and to determine the
cause of the poor performance of laboratories that used the anodic
stripping voltammetry methodology.
