No abstract

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Background: Most proficiency testing (PT) programs operate with an open design in which clearly identified performance samples are distributed directly to participating laboratories on a shipping schedule announced in advance. In this study, we examine the effectiveness of assessing clinical laboratory performance for blood lead with an open PT by comparing its results with a double-blinded testing protocol. Methods: Aliquots from up to 72 blood lead performance pools from the New York State Department of Health and the Wisconsin State Laboratory of Hygiene were disguised as routine patient specimens and submitted in two phases to up to 42 certified clinical laboratories for blood lead analysis. These 42 laboratories also received aliquots of the same performance samples for blood lead analysis directly from the “open” PT program provider. Results: Data reported under blind and open strategies were scored against acceptable target ranges using the Clinical Laboratory Improvement Amendments of 1988 (CLIA ’88) criteria established for blood lead, i.e., ± 0.19 μmol/L (± 4 μg/dL) or ± 10%, whichever is greater. Performance differences between the strategies were also assessed. We found that 17.7% of all blind PT results were classified as unacceptable compared with only 4.5% of open PT results (P <0.001). In phase 1, 13 of 22 laboratories (60%) exhibited a statistically significant difference (P <0.05) between their blind and open PT performances, although for 6 laboratories the poorer blind performance may not necessarily have led to unsuccessful PT participation under CLIA ’88 criteria. Seven (32%) laboratories had unsuccessful aggregate performance (<80%) under blind testing while maintaining successful performance in open testing. Of these seven, two had gross discrepancies motivating further investigation. Conclusions: The data suggest that although ∼60% of clinical laboratories make special efforts to improve analytical performance on open PT samples relative to performance achieved for routine patient specimens, in most cases the differences are clinically insignificant and would not likely affect cumulative PT performance. Occasional use of blind PT may deter the inclination to treat performance samples more carefully.

The new analyzer might be a useful tool for on-site monitoring of occupational lead exposures. The manufacturer's instructions should be adhered to with respect to specimen age and storage requirements.

A recently introduced hematofluorometer, the "Protofluor-Z" (Helena Laboratories, Beaumont, TX), has several novel features, most notably reporting units expressed as the molar ratio of zinc protoporphyrin (ZPP) to heme, i.e., micromoles of ZPP per mole of heme. We analyzed human blood specimens on the Protofluor-Z and by an ethyl acetate/acetic acid extraction procedure. Data from three laboratories were pooled and used to provide a comparison of the two methods. Results indicate that, with the Protofluor-Z, a value of 70 mumol of ZPP per mole of heme is approximately equivalent to the recommended screening cutoff of 35 micrograms of erythrocyte protoporphyrin per 100 mL of whole blood used in programs for pediatric lead-poisoning prevention. This empirically determined value is slightly lower than either that recommended by the manufacturer or a theoretical cutoff value that was determined mathematically.