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

Abstract Background There is current advocacy for change in Pb proficiency testing (PT) acceptance criterion from ± 4 μg/dl ([Pb] a ) to ± 2 μg/dl ([Pb] 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.