Stephen C. Hsu

Effect of Collection Tube Type and Preanalytical Handling on Myeloperoxidase Concentrations

BACKGROUND Myeloperoxidase (MPO) has shown potential as a marker for cardiovascular disease. Limited studies have been published with a variety of sample types, resulting in a wide range of MPO values. Little is known or understood about the impact of collection tube type and preanalytical handling of specimens for MPO determination. METHOD MPO concentration was determined by use of the ARCHITECT(R) MPO research use assay, which is currently under development. Samples were collected into multiple anticoagulant collection tubes from donors and patients presenting to the emergency department with symptoms of acute coronary syndromes. Whole blood was stored on ice or at room temperature for predetermined time periods. We also evaluated serum and plasma after centrifugation followed by storage at room temperature, 2-8 degrees C, and below -10 degrees C. RESULTS Baseline sample concentrations were dependent on collection tube type as well as handling conditions. MPO concentrations were consistently higher in samples collected in serum and heparin plasma tubes than in samples in EDTA or citrate tubes. Spike recovery was acceptable in all sera and plasma tested, indicating that the increased MPO concentrations were not due directly to an anticoagulant interference. CONCLUSIONS The collection tube type and preanalytical handling are critical for accurate and consistent MPO measurement. The preferred anticoagulant and tubes are the EDTA or EDTA plasma preparation tube. MPO concentrations in samples collected in these tubes are stable before centrifugation as whole blood as well as plasma after processing.

Evaluation of the Abbott ARCHITECT Toxo IgM assay

Development of the ARCHITECT Toxo IgM assay has been done to assist the clinician in acute Toxoplasma gondii infection detection, especially in pregnant women. Its use, in conjunction with ARCHITECT Toxo IgG and Toxo Avidity assays, will provide an array of assays particularly useful in the monitoring of pregnant females to determine the risk of maternal transmission of the parasite. Specificity results from 2 testing sites, using populations of pregnant females, hospital patients, and blood donors, demonstrated that the assay has an overall resolved relative specificity of 99.89% (confidence interval, 99.68-99.98%). Relative specificity for pregnant female specimens was 99.95% (n = 2031). Excellent seroconversion sensitivity was observed for the ARCHITECT Toxo IgM assay, which was similar to the Abbott AxSYM Toxo IgM assay (Abbott Laboratories, Abbott Park, IL). In more than 90% of the panels tested, the 1st bleed detected in the serial bleeds was the same for both assays.

Potential Interference by Antineutrophil Cytoplasmic Autoantibodies in Myeloperoxidase Immunoassays

Myeloperoxidase (MPO)1 has been identified as a potential marker of cardiovascular disease (1). As the clinical utility of new biomarkers is identified and commercial assays are developed, limitations on their use need to be identified and reported. Antineutrophil cytoplasmic autoantibodies (ANCAs) are known to exist in patients with diseases characterized by primary systematic vasculitis, such as Wegener granulomatosis, microscopic polyangiitis, and Churg– Strauss syndrome, and in those with idiopathic pauci-immune necrotizing crescentic glomerulonephritis, systemic lupus erythematosus, and rheumatoid arthritis (2). In particular, the immunofluorescence- staining pattern for perinuclear ANCAs (pANCAs) is associated with anti-MPO autoantibodies. pANCAs are most prevalent in microscopic polyangiitis (40%–80%), followed by Churg–Strauss syndrome (20%–30%) and Wegener granulomatosis (5%–20%). Autoantibodies can interfere with assays when the autoantibodies bind to analyte epitopes that are similar to those of the monoclonal antibodies used in the immunoassay. Anti-MPO autoantibodies are likely to bind to MPO in the sample and block or partially mask the epitopes necessary for binding to the antibodies used to capture and detect MPO. We evaluated the effect of MPO autoantibodies on the performance of the Cardio MPO™ immunoassay (PrognostiX), which has been cleared by the US Food and Drug Administration. We similarly evaluated an immunoassay under development for the Abbott ARCHITECT® instrument (Abbott …