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 µmol/L (9 µg/dL) and 3 additional specimens—each with an ABPb concentration of 0.33, 0.89, and 1.59 µmol/L (6.9, 18.4, and 32.9 µg/dL, respectively).
Outcome Measures
Misclassification error rates for reporting an elevation (
0.48 µmol/L [10 µg/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 µmol/L [9 µg/dL]), and the adjusted odds of a reported blood lead concentration differing from those of an ABPb concentration by more than 0.14 µmol/L (3 µg/dL).
Results
Blood lead results were obtained for 157 of 162 submissions. One laboratory reported all blood lead specimens as "below 0.48 µmol/L (10 µg/dL)." Two (11%) of 18 specimens with an ABPb concentration of 0.89 µmol/L (18.4 µg/dL) and 1 (6%) of 17 with an ABPb concentration of 1.59 µmol/L (32.9 µg/dL) were classified as below 0.48 µmol/L (10 µg/dL); 2 (11%) of 18 with an ABPb concentration of 0.33 µmol/L (6.9 µg/dL) and 44 (42%) of 104 with an ABPb concentration of 0.43 µmol/L (9 µg/dL) were classified as 0.48 µmol/L or greater ( 10 µg/dL). For specimens with an ABPb concentration of 0.43 µmol/L (9 µg/dL), the within-laboratory mean ranged from 0.23 to 0.52 µmol/L (4.8-10.7 µg/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 µmol/L (3 µg/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.
(Arch Pediatr Adolesc Med. 1996;150:609-614)
