Decreasing the cutoff for elevated blood lead (EBL) can decrease the screening sensitivity for EBL.

Change in the definition of elevated blood lead (EBL) from greater than or equal to 10 µg/dL (cutoff A) to greater than or equal to 5 µg/dL (cutoff B) was recently endorsed in the United States. A potential effect of this change is to decrease the screening sensitivity for EBL detection. We demonstrate this effect by simulated sampling of an example patient distribution for lead. Using lead-dependent assay imprecision, simulated sampling of the patient distribution tracked individual misclassifications relative to the EBL cutoff. Decreasing the EBL cutoff from A to B reduced screening sensitivity for EBL detection in this population to less than 90%, a decrease of 4%. The result was due to the fact that, for B, a greater fraction of the EBL population was near the EBL cutoff and therefore subject to misclassification due to assay imprecision. The effect of the decreased EBL cutoff to reduce EBL screening sensitivity is likely to apply to EBL screening programs generally.

Predicted effects of proposed tightened acceptance criterion for Pb proficiency testing (PT) on PT sample pass rates for Pb point-of-care testing.

BACKGROUND: There is current advocacy for change in Pb proficiency testing (PT) acceptance criterion from ± 4 µg/dl ([Pb] <40 µg/dl; criterion a) to ± 2 µg/dl ([Pb] <20 µg/dl, criterion b). We examined the effect of this proposed change on PT sample pass rates for point-of-care testing (POCT) as predicted by imprecision of POCT PT sample results. METHODS: Inter-site standard deviations (s) of POCT PT results were tabulated as a function of [Pb] and characterized as a linear function of [Pb] (r(2)>0.8). Given s, predicted minimum, random-error-only PT failure rates (Fp) as a function of [Pb] were computed as the fraction of a normal distribution of results ([Pb]± s) that would fall outside of boundaries of acceptance criterion a or b. RESULTS: For [Pb]=2-20 µg/dl, current observed PT sample failure rates using criterion a range from 3 to 6%, which are greater than the predicted minimum failure rates based on s alone (Fp(a)=0-6%). In contrast, predicted minimum failure rates based on s using criterion b are greatly increased (Fp(b)=5-35%). CONCLUSIONS: Given the degree of inter-site imprecision among POCT Pb PT results, adoption of criterion b for PT acceptance will dramatically increase Pb PT sample failure rates for POCT due to random-error alone.