Performance evaluation of a new fourth-generation HIV combination antigen-antibody assay.

Education and diagnostic tests capable of early detection represent our most effective means of preventing transmission of human immunodeficiency virus (HIV). The importance of early detection is underlined by studies demonstrating increased life expectancy following early initiation of antiviral treatment. The Elecsys(®) HIV combi PT assay is a fourth-generation antigen-antibody combination assay developed to allow earlier detection of seroconversion, and to have increased sensitivity and improved specificity. We aimed to determine how early the assay could detect infection compared with existing assays; whether all HIV variants could be detected; and the assay's specificity using samples from blood donors, routine specimens, and patients with potential cross-reacting factors. Samples were identified as positive by the Elecsys(®) assay 4.9 days after a positive polymerase chain reaction result (as determined by the panel supplier), which was earlier than the 5.3-7.1 days observed with comparators. The analytical sensitivity of the Elecsys(®) HIV combi PT assay for the HIV-1 p24 antigen was 1.05 IU/mL, which compares favorably with the comparator assays. In addition, the Elecsys(®) assay identified all screened HIV subtypes and displayed greater sensitivity to HIV-2 homologous antigen and antibodies to HIV-1 E and O and HIV-2 than the other assays. Overall, the specificity of the Elecsys(®) assay was 99.88 % using samples from blood donors and 99.81 % when analyzing unselected samples. Potential cross-reacting factors did not interfere with assay performance. The Elecsys(®) HIV combi PT assay is a sensitive and specific assay that has been granted the CE mark according to Directive 2009/886/EC.

Evaluation of chemiluminescence immunoassays for detecting thyroglobulin (Tg) and thyroid peroxidase (TPO) autoantibodies using the IMMULITE 2000 system.

The chemiluminescence assays for detection of autoantibodies to thyroid peroxidase (TPO) and thyroglobulin (Tg) implemented on the IMMULITE 2000 system (Diagnostic Products Corporation) were evaluated. These were immunometric assays with antigen-coated beads and monoclonal murine anti-IgG antibodies conjugated with alkaline phosphatase. Precision was satisfactory with an intraassay precision of 5.3-5.5% for anti-Tg and 4.8-5.3% for anti-TPO and an interassay precision of 5.7-7.3% for anti-TPO and 5.2-7.5% for anti-Tg. The lower detection limit was determined as 5 IU/ml for anti-TPO and 2.2 IU/ml for anti-Tg. The average dilution linearities of 102% for anti-TPO and 100% for anti-Tg and the average recovery of 80-127% for anti-TPO and 93-112% for anti-Tg were acceptable. The findings of the tests were compared with the systems from Pharmacia & Upjohn, ORGenTec, Roche Diagnostics, Byk Sangtec Diagnostica and BRAHMS Diagnostica. Taking the respective cutoff value into account, concordance was 87-96% for anti-Tg and 87-97% for anti-TPO. Summarizing all results from the different methods revealed a clinical agreement of 95% for anti-TPO and 93% for anti-Tg. A good agreement was found with the IMMULITE anti-TPO and anti-Tg assays, which are closely related as regards method and biochemistry. Regression analysis gave the following results: anti-TPO IMMULITE 2000 vs anti-TPO IMMULITE: anti-TPO IMMULITE 2000 = 0.99 x IMMULITE anti-TPO - 1.43 IU/ml (r = 0.99, n = 144). anti-Tg IMMULITE 2000 vs anti-Tg IMMULITE: anti-Tg IMMULITE 2000 = 0.98 x IMMULITE anti-Tg + 1.63 IU/ml (r = 0.99, n = 86). Further age-dependent normal ranges were evaluated. A higher prevalence of elevated autoantibody titers was found for patients older than 50 years. The rate of elevated antibody titer can be reduced by using an age-dependent reference range: < or = 50 years anti-TPO < 35 IU/ml, anti-Tg < 40 IU/ml and > 50 years anti-TPO < 100 IU/ml, anti-Tg < 80 IU/ml. Further samples from clinically diagnosed Hashimoto's thyroiditis and Graves' disease were investigated. The levels of positive anti-Tg values and anti-TPO values accorded with those stated in the literature and were comparable to those measured with a reference assay. In the tested INSTAND e. V. interlaboratory samples there was high-level accordance with the expected clinical results.