Performance validation of a third-generation allergen-specific IgE assay in the clinical laboratory: interlaboratory and intermethod comparison.

BACKGROUND: Allergen-specific IgE (sIgE) measurements are used to help identify causative allergenic agents and to determine the degree of sensitization to facilitate treatment decisions. We examined the performance of a new third-generation chemiluminescent enzyme immunoassay for allergen-specific IgE (sIgE) on the continuous random access Immulite 2000 system. METHODS: Detection limit and dilutional linearity were determined. Within-run and total precision were assessed according to the NCCLS EP5 guideline. Interlaboratory comparison of the new Immulite 2000 third-generation allergen-specific IgE assay was performed, as well as intermethod comparison against the Pharmacia FEIA, a second-generation assay. RESULTS: The detection limit was <0.1 kU/l. Dilutional linearity held from 100 down to 0.2 kU/l. Regression analysis of the interlaboratory comparison results yielded: Immulite 2000(Laboratory 1)=1.07 Immulite 2000(Laboratory 2)+0.18 kU/l; r=0.98, n=3588 results. Intermethod comparison showed the following: Immulite 2000=0.83 (Pharmacia FEIA)+0.42 kU/l; r=0.79, n=512 results. Bland-Altman analysis of the interlaboratory and intermethod comparisons indicated no systematic bias. CONCLUSIONS: We confirmed the reported performance characteristics of the third-generation sIgE assay and found reasonably good interlaboratory and intermethod agreement. The extended range capability of the third-generation assay provides a new tool for investigating cutoffs and trends in childhood allergy disease progression at concentrations <0.35 kU/l.

Signify ER Drug Screen Test evaluation: comparison to Triage Drug of Abuse Panel plus tricyclic antidepressants.

Signify ER Drug Screen Test (Signify ER) and Triage Drug of Abuse Panel plus TCA (Triage DOA Panel) rapid drug screening devices were compared at four laboratories. Both assay systems are point of care immunoassays, measuring phencyclidine, barbiturates, amphetamine, cocaine metabolite, methamphetamine, tricyclic antidepressants, opiates, marijuana metabolite, and benzodiazepines in human urine. The performance of these two assay systems, including a cutoff verification and cross-reactivity using spiked urine specimens and accuracy using clinical urine samples, was investigated. The cutoff verification study showed that the Signify ER had 95.4% precision for all drugs tested at concentrations of 50%, 75%, 125%, 150%, and 200% of cutoffs compared to 90% precision obtained with Triage DOA Panel. Accuracy studies testing 53 negative urine samples demonstrated that both Signify ER and Triage DOA Panel have 100% specificity. Testing of 693 positive urine samples demonstrated that Signify ER and Triage DOA Panel have sensitivities of 99.8% and 99.3%, respectively, with an accuracy of 99.9% and 99.6%. A total of 527 compounds were tested for the cross-reactivity study. Eighty-seven structurally related drugs and metabolites were found to cross-react with at least one of the nine tests of the Signify ER. Four hundred forty structurally unrelated compounds that can be found in human urine were shown not to cross-react with the Signify ER. In terms of operating characteristics, the Signify ER device is simpler since only a single pipetting step is required, and reaction completed within 8 min.