Analytical performance and clinical results of a fully automated MEIA system for brain natriuretic peptide assay: comparison with a point of care testing method.

The aim of this study was to evaluate the analytical performance of a recently available immunoassay for brain natriuretic peptide (BNP), based on microparticle enzyme immunoassay (MEIA, AxSYM System, Abbott Laboratories), whose analytical characteristics and clinical results were compared with those of a point of care testing (POCT) method (TRIAGE system, Biosite Diagnostics). The within-run and total imprecision of the MEIA system were 18.4% and 19.8% at 21 ng/l, 8.0% and 14.8% at 183 ng/l, and 5.7% and 14.0% at 319 ng/l, respectively. The detection limit of the MEIA system was tested by repeatedly measuring (n=20) the 0 calibrator in four different runs; a mean +3 SD value of 5.6+/-4.8 ng/l (range 1.8-12.6 ng/l) was obtained. A close linear relationship (MEIA= -22.5+/-1.71 POCT method, R=0.950, n=296) was found (BNP concentration: 5-5500 ng/l), with a significant bias (mean difference: 164.8 ng/l, p<0.0001). Mean BNP concentration measured in 94 reference subjects (57 women and 37 men; mean age 43.5+/-14.0 years) was higher with MEIA than POCT, (25.9+/-32.7 ng/l vs. 11.7+/-8.9 ng/l, p<0.0001). The same trend was observed also in 202 cardiac patients (620.6+/-1082.2 ng/l vs. 386.1+/-594.5 ng/l, p<0.0001). Our data suggest that MEIA and POCT have quite similar analytical performance but different clinical results. Then, different reference values, as well as cut-off values, should be taken into account for the clinical use of these two immunoassays.

Multicenter comparison of first- and second-generation IMx tacrolimus microparticle enzyme immunoassays in liver and kidney transplantation.

Tacrolimus is a potent immunosuppressive drug successfully used for baseline and rescue immunosuppression in patients after liver and kidney transplantation. Data from several clinical trials have demonstrated the efficacy of tacrolimus in the prevention of allograft rejection, even at lower concentrations in the therapeutic range (5-15 microg/L). In fact, some patients with tacrolimus levels at less than 5 microg/L have excellent hepatic or kidney function. The limit of detection of the IMx Tacrolimus I assay (TAC I; Abbott Laboratories, IL) is only 5 microg/L and that of the lower tacrolimus calibrator is 10 microg/L. The second-generation assay uses the same monoclonal antibody and the same IMx technology but offers improved sensitivity, with a dynamic range from 0 microg/L to 30 microg/L (lower calibrator, 3 microg/L). The aim of this multicenter study was to evaluate the new IMx Tacrolimus II assay (TAC II) by assessing its precision, sensitivity, performance, and correlation degree relative to the IMx TAC I assay. The study was performed at three centers in Spain. The within-run coefficients of variation (CVs) obtained for the new assay, using each of the trilevel controls in replicates of 20 during 3 consecutive days, were 8.06%, 4.38% and 5.09% at 5 microg/L, 11 microg/L, and 22 microg/L, respectively. The corresponding between-run CVs obtained measuring each of the three controls in duplicate on 10 consecutive days were 9.54%, 6.38% and 5.75%. The limit of detection, with 97.5% confidence, was 1.22 microg/L. TAC II results (Y) were compared with those from the original TAC I assay (X) analyzing 293 whole blood samples from liver (n=145) and kidney (n=148) transplant recipients. The correlation study with patient samples (using the Passing-Bablock method) was y=1.056, x + 0.017, r=0.927. No statistically significant differences were observed between assays (TAC I versus TAC II) in the mean values obtained for total patients (9.89+/-5.42 microg/L versus 10.49+/-5.63 microg/L), liver patients (9.16+/-4.79 microg/L versus 10.00+/-5.20 microg/L), and kidney patients (10.62+/-5.87 micro g/L versus 10.98+/-5.99 microg/L). The new IMx TAC II assay demonstrated the same precision and accuracy that characterized the original assay but showed improved sensitivity to the demands of tacrolimus monitoring in the lower therapeutic range of drug concentrations.

Detection of Chlamydia trachomatis in semen by antibody-enzyme immunoassay compared with polymerase chain reaction, antigen-enzyme immunoassay, and urethral cell culture.

OBJECTIVE: To compare the results obtained by four different techniques for the detection of Chlamydia trachomatis in the male genital tract. DESIGN: Prospective study. SETTING: Andrology unit of a university hospital. PATIENTS: Male infertility patients. INTERVENTIONS: Analysis of semen samples and urethral swabs for the presence of C. trachomatis by recombinant antibody-enzyme-linked immunosorbent assay (rELISA), polymerase chain reaction (PCR), antigen-enzyme immunoassay (EIA) and McCoy cell culture. MAIN OUTCOME MEASURE: Detection of C. trachomatis. RESULTS: In 57 of 205 semen samples (27.8%) immunoglobulin A-antibodies against C. trachomatis were found. In contrast, only 1 of 56 semen samples (1.8%) was positive for C. trachomatis-DNA by PCR, only 1 of 139 semen samples (0.7%) was positive by antigen-EIA, and only 4 of 173 urethral swabs (2.3%) grew C. trachomatis in cell culture. CONCLUSIONS: The discrepancy of positive results found by the antibody-rELISA and direct methods for the detection of C. trachomatis indicates successful eradication of the microorganism in > 90% of antibody-positive men. Therefore, detection of antibodies against C. trachomatis in seminal plasma appears to be of limited diagnostic value.

Dot-Enzyme-Linked immunosorbent assay (Dot-ELISA) for detection of pneumococcal polysaccharide antigens in pleural fluid effusion samples: comparison with bacterial culture, counterimmunoelectrophoresis and latex agglutination

Dot-ELISA para deteccao de antigenos polissacaridicos de pneumococos foi padronizado em vista da necessidade de se ter um diagnostico rapido e eficaz para pneumonia pneumococica aguda. Um total de 480 amostras de liquido pleural sendo 442 de criancas com diagnostico clinico e laboratorial de pneumonia bacteriana e 38 de pacientes com tuberculose, mais 20 amostras dos soros sanguineos de criancas sadias foram avaliados no Dot-ELISA. As amostras foram tratadas previamente a 90ºC por 10 min com EDTA 0,1 M de pH 7,5 e aplicadas sobre membrana de nitrocelulose. Para a deteccao de antigeno pneumococico foi empregado omniserum pneumococico diluido a 1:200. Os resultados de Dot-ELISA avaliados em comparacao com os resultados de cultura bacteriana, contra-imunoeletroforese e latex-aglutinacao apresentaram indices de 0,940 para a sensibilidade, 0,830 para especificidade e 0,760 para concordancia. Omniserum pneumococico mostrou ser um otimo soro polivalente para a deteccao de antigenos pneumococicos em Dot-ELISAe, essa tecnica provou se uma alternativa pratica e eficaz para o diagnostico de pneumonias pneumococicas.