Automated Microparticle Enzyme Immunoassay Research Articles

Response to anti-HBV vaccine and 10-year follow-up of antibody levels in healthcare workers

BackgroundDespite improvements in public health and antiviral treatments, vaccination is still the most effective means of prevention of hepatitis B virus (HBV) infection. However, little is known about the duration of protection given by the anti-HBV vaccine. Healthcare workers represent a category at risk not only of contracting infection but also of being a source of contagion to patients. ObjectivesTo assess individual responses to the anti-HBV vaccine and duration of protection 10 years after its administration in a cohort of healthcare workers employed by the University Hospital ‘G. Martino’ in Messina, Italy. MethodsOne hundred and seventy medical staff who had been vaccinated following an incident carrying risk of HBV infection were included in this study. The group was followed over a 10-year period, and HBV antibody levels were assessed using an automated microparticle enzyme immunoassay. ResultsProtective antibody levels (≥10 mIU/ml) were found in 65% of subjects who had completed the full vaccine schedule (three doses) and in 35% of subjects who had only received one or two doses of anti-HBV vaccine. Moreover, 10 years after vaccination, HBV antibody levels were inversely related to age at vaccination (P < 0.001). No differences were found between males and females. ConclusionsThis study, in line with the literature, shows the importance of completing the full vaccine schedule (three doses). Moreover, in order to have an effective and durable antibody response and avoid the risk of contracting HBV after an injury at work, it is important to recommend anti-HBV vaccination at a young age, ideally during childhood in accordance with the national vaccination policy.

Holotranscobalamin is not influenced by decreased renal function in elderly men: the MrOS Sweden study

Subclinical cobalamin deficiency is common in the elderly, but the sensitivity and specificity of serum total cobalamin for this diagnosis is poor. Serum holotranscobalamin (holoTC), a measure of biologically available cobalamin, is considered a better marker for early cobalamin depletion than total cobalamin. However, in elderly populations, health-related reference intervals for holoTC and correlations to renal function are not entirely clear. HoloTC was determined with an automated microparticle enzyme immunoassay (AxSYM®) in 790 elderly non-vitamin-supplemented Swedish men, median age 75.3 years. Renal function was assessed with creatinine, cystatin C and estimated glomerular filtration rate (eGFR calculated from creatinine). Median holoTC was 51.8 pmol/L, the health-related reference interval 19.6-132.3 pmol/L. There was no significant difference in mean holoTC in probands with normal compared to high creatinine (P = 0.80) and cystatin C (P = 0.82). No significant differences between the quartiles of creatinine or cystatin C in mean of log holoTC were seen. HoloTC correlated strongly with total cobalamin (r = 0.69, P < 0.001), weaker with eGFRcreatinine (r = -0.09, P < 0.05) and creatinine (r = 0.09, P < 0.05), the latter correlation was only seen in subjects with creatinine <100 µmol/L. HoloTC correlated negatively with plasma total homocysteine (r = -0.24, P < 0.001), but not with cystatin C and age. Serum holoTC in healthy elderly men shows the same distribution as earlier described for a younger reference population. In this group of elderly subjects, holoTC did not correlate to reduced renal function. Thus, holoTC appears to be a promising tool for evaluating cobalamin status also in elderly populations.

Effect of Early Posttransplantation Tacrolimus Concentration on the Development of Acute Graft-versus-Host Disease after Allogeneic Hematopoietic Stem Cell Transplantation from Unrelated Donors

Only limited data are available regarding the relationship between blood concentration of tacrolimus and its efficacy in preventing acute graft-versus-host disease (aGVHD). We retrospectively evaluated the effects of the whole blood concentration of tacrolimus, which was measured by an automated microparticle enzyme immunoassay, early after allogeneic hematopoietic stem cell transplantation (HSCT) upon the development of aGVHD. Sixty patients, who underwent allogeneic HSCT from serologically human-leukocyte antigen-matched unrelated donors and received continuous infusion of tacrolimus with short-term methotrexate for GVHD prophylaxis, were included in this study. The target range of the blood concentration of tacrolimus was set at 10 to 20 ng/mL, and the level was maintained within this range in all patients. However, the mean blood concentration of tacrolimus during the third week after HSCT was significantly associated with the grades of aGVHD (17.3 ± 2.1 in patients with grades 0-I vs 15.9 ± 2.8 in II-IV and 14.8 ± 2.1 in III-IV; P < .05 and <.01, respectively). Multivariate analysis also demonstrated that higher age (≥35) of donor(odds ratio [OR] = 4.28) and lower mean blood concentrations of tacrolimus during the second (OR = 0.75; 95% confidence interval [CI]: 0.58-0.98) and third weeks (OR = 0.76; 95% CI: 0.58-0.98) after HSCT were significant risk factors for grades II-IV aGVHD (P < .05). We conclude that the early posttransplantation blood concentration of tacrolimus had a significant impact on the development of moderate-to-severe aGVHD after allogeneic HSCT from an unrelated donor.

Overcoming the effect of rifampin on the tacrolimus metabolism by itraconazole administration in an allogeneic hematopoietic stem cell transplant recipient

Rifampin, one of the first-line agents for tuberculosis, has a great potential to induce the activity of the cytochrome P450 (CYP) enzyme, CYP 3A4, and lowers the concentration of calcineurin inhibitors such as tacrolimus and cyclosporine A (CsA). When calcineurin inhibitors and rifampin are coadministered, increasing the dose of calcineurin inhibitors is essential in maintaining therapeutic blood levels, but this often fails and results in the induction of graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (HSCT) or graft rejection after solid organ transplantation [1–6]. Another option is the administration of agents which could compete with the activity of rifampin upon CYP 3A4. We here present a case in which rifampin was coadministered with tacrolimus after allogeneic HSCT, and administration of oral-solution itraconazole successfully offset the effect of rifampin on the tacrolimus metabolism, resulting in the achievement of a therapeutic blood level of tacrolimus. A 50-year-old woman with myelodysplastic syndrome underwent bone marrow transplantation from an unrelated donor. Tacrolimus and short-term methotrexate were given for the prophylaxis of GVHD. Tacrolimus was given at an initial dose of 0.03 mg/kg by continuous intravenous infusion from day -1, and its dose was adjusted to maintain its blood level at 15–20 ng/ml during the first 4 weeks, followed by oral administration to maintain the blood level at 5–10 ng/ml. She developed acute GVHD of the skin on day 33 post-transplant, which was successfully treated with prednisolone. Prednisolone was given at a dose of 1 mg/kg for 7 days, then tapered, and discontinued on day 96 posttransplant. During prednisolone therapy, voriconazole at dose of 400 mg/day was orally given for the prophylaxis of fungal infection. Antifungal agents were not given thereafter. Around day 150 post-transplant, when tacrolimus was still being orally administered (3 mg/day) and its whole-blood trough level was around 5.5 ng/mL, pulmonary tuberculosis was diagnosed. Anti-tuberculosis chemotherapy consisting of rifampin (300 mg/day), isoniazid (300 mg/day), ethambutol (750 mg/day), and pyrazinamide (1200 mg/day) was initiated. Shortly after initiating this combination therapy, the trough level of tacrolimus became undetectable by automated microparticle enzyme immunoassay (minimum detectable level: 3.0 ng/ mL). Doubling the dose of tacrolimus to 6 mg/day failed to achieve a detectable level of tacrolimus. Oral-solution itraconazole was then initiated at a dose of 200 mg/day for the prophylaxis of fungal infection. The trough level of tacrolimus began to rise, and reached 5.7 ng/ml with 3 mg/ day of oral tacrolimus in 8 days after initiating itraconazole. The patient did not develop GVHD during or after the period of undetectable blood levels of tacrolimus, and fungal infection throughout the clinical course. The combination antituberculosis therapy was effective, and the pulmonary tuberculosis was cured after the 12-month therapy. Coadministration of oral-solution intraconazole with tacrolimus, rifampin, and three other anti-tuberculosis agents caused no clinically significant adverse events. As seen in the present case, rifampin has a great impact on the pharmacokinetics of calcineurin inhibitors, and markedly increases the dose requirement of calcineurin inhibitors to maintain a therapeutic blood level during rifampin therapy [1]. Increasing the dose of calcineurin inhibitors is not always effective, and the reduced levels T. Mori (&) Y. Aisa J. Kato Y. Nakamura T. Shimizu S. Okamoto Division of Hematology, Department of Medicine, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan e-mail: tmori@sc.itc.keio.ac.jp

Diagnostic Utility of AxSYM Anti-Cyclic Citrullinated Peptide Antibody Assay

The presence of rheumatoid factor (RF) is one of the classification criteria of the American College of Rheumatology (ACR) for rheumatoid arthritis (RA), but it has a limitation of low specificity. We compared the diagnostic utility of anti-cyclic citrullinated peptide (CCP) antibodies analyzed by an automated immunoassay system with that measured by a 96 well plate ELISA method. The RF and anti-CCP antibodies were determined in 172 serum samples: 52 RA patients, 73 disease controls (systemic lupus, Sjogren's syndrome, palindromic rheumatism), and 47 healthy controls. Anti-CCP antibodies were measured by DIASTAT 96 well plate ELISA method (Axis-Shield Diagnostics, UK) and AxSYM automated microparticle enzyme immunoassay system (Abbott Laboratories, USA). RF was assayed by latex immunoturbidimetry (Toshiba 200 FR, Japan). The diagnostic performances of these tests were compared using a ROC curve analysis, and linearity and precision analysis of AxSYM anti-CCP was carried out. The sensitivities of RF, DIASTAT anti-CCP, and AxSYM anti-CCP were 78.8%, 84.6%, and 82.7%, respectively and the specificities were 72.5%, 88.3%, and 88.3%, respectively. On ROC curve analysis, the area under the curve was 0.924 for AxSYM anti-CCP, 0.886 for DIASTAT anti-CCP, and 0.847 for RF. AxSYM anti-CCP showed a good linearity, and within-run and total-run precision. Diagnostic performance of automated AxSYM anti-CCP assay was comparable to that of DIASTAT 96 well plate ELISA method. AxSYM anti-CCP assay has an advantage of random access capability and will be useful in laboratories with low sample number and/or with a need of rapid turnaround time.

Blood pressure reduction due to hemoglobin glycosylation in type 2 diabetic patients

To test the hypothesis that glycosylation of hemoglobin constitutes a risk factor for hypertension. A total of 129 relative uniform diabetic subjects (86 women and 42 men) were enrolled in a cross-sectional study. Exclusion criteria included alcohol consumption, smoking, ischemic heart disease, stroke, neoplasia, renal, hepatic, and chronic inflammatory disease. Systolic and diastolic pressures were recorded in subsequent days and mean arterial blood pressure (MAP) was determined. Hemoglobin glycosylation was measured by determining the percentage glycosylated hemoglobin (HbAlc) by means of the automated microparticle enzyme immunoassay test. MAP was found to be independent of the concentration of HbA1c; however, correcting MAP for the variability in hematocrit, to evidence the level of vasoconstriction (or vasodilatation) showed that MAP is negatively correlated with the concentration of HbA1c (p for trend <0.05), when patients treated for hypertension are excluded from the analysis. Patients treated for hypertension showed the opposite trend with increasing MAP as HbAlc increased (p for the difference in trends <0.05). Glycosylation per se appears to lead to blood pressure reduction in type 2 diabetic patients untreated for hypertension. Treatment for hypertension may be associated with a level of endothelial dysfunction that interferes with the antihypertensive effect of HbA1c.

Poor response to 18‐month lamivudine monotherapy in chronic hepatitis B patients with IgM anti‐HBc and acute exacerbation

Appearance of immunoglobulin class M antibody against hepatitis B core antigen is a predictor of beneficial response to interferon-alpha therapy in chronic hepatitis B patients, but its relationship with the efficacy of lamivudine therapy remains unclear. To investigate the outcome of lamivudine therapy in chronic hepatitis B patients with immunoglobulin class M antibody against hepatitis B core antigen and acute exacerbation. Chronic hepatitis B patients with acute exacerbation receiving a national-wide therapeutic trial of 18-month lamivudine monotherapy were enrolled for the analysis. Four consecutive seronegative patients were recruited as individual matching controls of one positive subject. Immunoglobulin class M antibody against hepatitis B core antigen in serum was assayed monthly by an automated microparticle enzyme immunoassay. Fifteen (8.9%) of 167 chronic hepatitis B patients with acute exacerbation were seropositive for IgM anti-HBc. Thus 60 seronegative patients were consecutively recruited as control group. At the end of therapy, two (13.3%) of the 15 seropositive patients achieved a sustained response, significantly lower than 26 (43.3%) of the control group. Appearance of immunoglobulin class M antibody against hepatitis B core antigen in chronic hepatitis B patients with acute exacerbation is a predictor of poor response to lamivudine monotherapy. This is clinically relevant to the decision-making in treating chronic hepatitis B patients with acute exacerbation.

Elevated concentrations of C-reactive protein in subjects with Type 2 diabetes mellitus are moderately influenced by glycemic control

The aim of this study was to establish whether glycemic control results in decrease of C-reactive protein (CRP) in Type 2 diabetic subjects. Newly diagnosed Type 2 diabetic subjects were recruited and followed-up by 6-month intensive medical management. All the participants were carefully interviewed, clinically examined, and laboratory tested to exclude conditions likely to provoke an inflammatory response, which was an exclusion criterium. CRP was measured by automated microparticle enzyme immunoassay (IMx, Abbott Laboratories, USA). Two-hundred and forty-eight patients were included in the analysis of data. At baseline, average CRP levels were of 9.6 +/- 6.2 mg/l. Only 14 (5.7%) patients showed a fasting glucose equal or lower than 6.1 mmo/l (5.6 +/- 0.4 mmo/l); of them, 6 (42.8%) had elevated CRP levels (8.8 +/- 6.7 mg/l). The fasting glucose in the 234 (94.3%) non-controlled subjects was 13.1 +/- 4.8 mmol/l; of them 179 (76.5%) subjects showed elevated CRP levels (10.9 +/- 6.5 mg/I). At the end of the 6-month follow-up, the average fasting glucose and HbA1c in the overall group decreased from 12.5 +/- 5.0 to 9.0 +/- 1.6 mmol/l, p < 0.00001, and 13.0 +/- 4.9 to 8.9 +/- 2.9%, p < 0.00001, which resulted in a significant reduction of CRP levels (9.6 +/- 6.2 to 6.3 +/- 3.0 mg/l, p < 0.00001). Seventy-one (28.6%) patients reached glycemic control; however, only 29 (40.8%) of them reduced the CRP levels to 3 mg/l or less (1.3 +/- 1.9 mg/l), and the remaining 42 controlled patients maintained high CRP concentration (4.2 +/- 1.2 mg/I), p < 0.00001. Concentration of CRP is moderately influenced by glycemic control in the Type 2 diabetic subjects.

Serum Ig E Concentration In Acute Pulmonary Thromboembolism

Background : Events mediated by immunoglobulin E (IgE) may be related to platelet activation and aggregation, and serum IgE concentrations may increase in various vascular diseases such as previous myocardial infarction, previous stroke and current large-vessel peripheral arterial disease. There may be an association between serum IgE and acute pulmonary thromboembolism (PTE). Objectives : The aim of the study was to evaluate serum IgE concentrations in patients with acute PTE. Methods : Twenty-two patients with a diagnosis of acute PTE were included in the study. Serum IgE concentrations were measured by an automated microparticle enzyme immunoassay at the time of diagnosis and 5th, 15th, and 30th days after the diagnosis. Because serum IgE concentrations follow a log-normal distribution, all subsequent analysis were performed on a log transformed scale and geometric mean values were used. The Wilcoxon matched-pairs signed-ranks test was applied for paired analysis. Results : Serum IgE concentrations (geometric mean ± SEM) were 1.90 ± 0.15, 1.91 ± 0.16, 1.82 ± 0.15, and 1.76 ± 0.15 at the time of diagnosis and 5th , 15th, and 30th days after the diagnosis, respectively. Serum IgE concentrations were not significantly different between at the time of diagnosis and 5th day after the diagnosis. However, serum IgE concentrations were significantly lesser at the 15th and 30th days after the diagnosis than serum IgE concentrations at the time of diagnosis and at 5th days after the diagnosis (p < 0.001). Conclusions : The data evaluating serum IgE concentrations in patients with acute PTE is limited and, to our knowledge, until now there has been only one study. Our study showed that serum IgE concentrations that were detected at the time of diagnosis of acute PTE significantly lessen with treatment at the 15th and 30th days after the diagnosis.

Detection of human immunodeficiency virus type 1 and type 2 antibodies by a new automated microparticle immunoassay AxSYM HIV-1/HIV-2

A new automated microparticle enzyme immunoassay (MEIA) for the AxSYM instrument developed recently by Abbott Laboratories was compared with two established assays i.e. HIV-1/HIV-2 3rd Gen. Plus EIA (Abbott, Delkenheim, FRG) and Wellcozyme HIV 1 + 2 (Murex Diagnostics, Dartford, England) devised for the detection of human immunodeficiency virus type 1 (HIV-1) and HIV-2 antibodies. A total of 7293 serum samples were tested by the AxSYM HIV-1/HIV-2. The test panel included seroconversions ( n = 22), samples from HIV-1 and HIV-2 positive individuals, hospitalized patients, blood donors, high risk individuals. To challenge further the specificity of the assays, large numbers of EIA repeatedly reactive but Western blot negative samples, potentially cross-reactive sera, Western blot indeteiminate specimens and samples from pregnant women were tested. In four seroconversion panels, HIV-1 infection was detected one bleed earlier with the AxSYM HIV-1/HIV-2 than with the Abbott HIV-1/HIV-2 3rd Gen. Plus EIA. Although the AxSYM HIV-1/HIV-2 was tested with a higher number of challenging sera than the alternative assays, the specificity was very high (99.4%). The highest number of false positive results was obtained with serum samples that were repeatedly reactive in EIAs different from those compared in the present study. The automated AxSYM system permits the testing of a large sample number in a rapid turn-around time and by random access urgent tests can be carried out even when an assay is in progress.

Differential diagnosis of acute HBsAg positive hepatitis using IgM anti-HBc by a rapid, fully automated microparticle enzyme immunoassay

Background/Aims: We determined the diagnostic significance of IgM anti-HBc by a rapid, fully automated microparticle enzyme immunoassay (IMx CORE-M) in acute HBsAg positive hepatitis. Methods: We studied prospectively for at least 6 months 100 patients with acute self-limited hepatitis B (group A) and 40 patients with acute hepatitis superimposed on histologically confirmed chronic hepatitis B (group B). On admission, all patients in group A were positive and those in group B were negative for IgM anti-HBc by a commercially available enzyme immunoassay. Results: Based on the assay criteria, the rates of IMx CORE-M ( > 1.2) positive serum samples on admission, 4, 12 and 24 weeks later were: in group A: 100%, 95%, 72%, 44% and in group B: 20%, 27.5%, 17.5%, and 15%, respectively. Misclassification was observed in 20-27.5% of the acute on chronic hepatitis B cases. However, the mean IMx CORE-M index value was found to be significantly higher in group A during the whole follow-up. In particular, on admission the mean IMx CORE-M index value weas 2.504±0.435 (range: 1.508–3.482)_ in group A and 0.747±0.346 (range: 0.062–1.384) in group B ( p<0.001). Discriminant function analysis showed that the cutoff level between the two groups for IMxCORE-M index on admission was 1.5. Four to 12 weeks from admission, in the group with acute on chronic hepatitis B cases, 13 patients with HDV and/or HCV superinfection had significantly lower IMx-CORE M index values compared with 27 patients with acute hepatitis due to exacerbation of chronic hepatitis B. Conclusions: IMx CORE-M appears to be an accurate diagnostic test to differentiate acute from acute on chronic HBsAg positive hepatitis, but the cut-off level seems to be higher (1.5 instead of 1.2).

HPLC-microparticle enzyme immunoassay specific for tacrolimus in whole blood of hepatic and renal transplant patients

Tacrolimus is a relatively new immunosuppressant used in organ transplantation to prevent graft rejection. However, its use is not devoid of side effects, making it important to maintain blood concentrations within therapeutic ranges. Several analytical methods are currently available for routine drug monitoring. However, these methods are based on use of the same monoclonal antibody, which also cross-reacts with some metabolites, resulting in overestimation of some blood concentrations. Even though this antibody appears appropriate for therapeutic drug monitoring, no reference method measures only the parent drug, mainly because of the poor absorptivity of tacrolimus in ultraviolet light. We have developed a method displaying an increased specificity towards the unchanged drug, using conventional equipment available in most clinical laboratories. After chromatographic separation of the blood extract, the tacrolimus fraction is analyzed by an automated microparticle enzyme immunoassay (MEIA) performed on the IMx analyzer (Abbott Labs.). This method is linear from 0 to 40 micrograms/L, yields CVs from 8.5% to 18.2%, and has a detection limit of 5 micrograms/L. Tacrolimus concentrations obtained by HPLC-MEIA in hepatic and renal transplant patients are from 47.5% to 18.8% lower than those obtained by MEIA, according to liver function tests and metabolite accumulation, even though no significant differences were observed between the methods for drug-free blood samples supplemented with known amounts of tacrolimus.

Maternal serum CA 125 levels in pregnancies with chromosomally-normal and -abnormal fetuses. Dutch Working Party on Prenatal Diagnosis.

We measured the maternal serum cancer antigen 125 (MS-CA 125) levels in 98 nonpregnant women, 765 first- and second-trimester pregnancies with chromosomally-normal fetuses, and 54 chromosomally-abnormal pregnancies. To determine the MS-CA 125 concentration, we used a new automated microparticle enzyme immunoassay with low inter-assay variability. The median MS-CA 125 level decreased from the first to the second trimester of pregnancy and was higher than that in non-pregnant women. We found no difference between normal and Down's syndrome (n = 29) pregnancies (t-test: t = 0.57, p > 0.5). The MS-CA 125 levels in pregnancies with other chromosomal abnormalities showed no difference either, compared with the normals. We conclude that MS-CA 125 is not a useful marker for fetal Down's syndrome, nor for other chromosomal disorders in pregnancy.

Comparison of an ELISA system for the quantification of hepatitis B antibody with an automated and a semi-automated system

In order to manage the increased workload resulting from post vaccination hepatitis antibody testing of health care workers, the anti-hepatitis B ELISA assay ETI-AB-AUK (Sorin Biomedica), adapted for quantification using standards available as an addition to the qualitative kit assay ((ABAU-STD-SET, (Sorin Biomedica)) and a sample pre-dilution step, was compared with a fully automated microparticle enzyme immunoassay IMX AUSAB (Abbott Laboratories), and a semi-automated enhanced luminescence system (Amerlite Amersham, now Kodak). Seventy-eight samples were concurrently tested and analysed statistically using a Regression Coefficient computer package (Apple Mackintosh Cricket). Good quantitative agreement was observed with ELISA vs IMX giving a linear correlation coefficient ( r = 0.96). The linear correlation coefficient for ELISA vs Amerlite was r = 0.77. This study validates the use of the automated IMX system and allows the comparison of IMX results with previous ‘semi-quantitive’ ELISA results when longitudinally assessing patients response to a recombinant hepatitis B vaccine.

Automated microparticle enzyme immunoassay for neural thread protein in cerebrospinal fluid from Alzheimer's disease patients.

An automated microparticle enzyme immunoassay (MEIA) with the IMx analyzer for the detection of neural thread protein (NTP) in cerebrospinal fluid (CSF) from Alzheimer's disease (AD) patients was developed. This assay uses monoclonal antibodies produced against the purified pancreatic form of the protein. The assay employs one monoclonal antibody covalently coupled to the microparticle to capture immunoreactive material in CSF or brain tissue. The second monoclonal antibody was conjugated to alkaline phosphatase and serves as detection antibody. The assay provides results in approximately 45 minutes with a sensitivity of 60 pg/ml (3 fmoles/ml). The titration curve of both normal and AD CSF resulted in a linear relationship with respect to the volume of CSF used. A similar relationship was observed when normal and AD brain tissue extracts were serially diluted. The molecular weight of NTP in CSF was approximately 20 kD as determined by gel filtration method under non-denaturing conditions. The recovery for pancreatic thread protein (PTP) spiked in either normal or AD CSF was 104% and 108%, respectively. Intra-, inter-, and total assay CVs (coefficient of variation) for controls were less than 2.9%, 3.3% and 3.0%, respectively. This assay will provide a useful tool in the study of the Alzheimer's disease and may help research in diagnosis and prognosis of Alzheimer's disease and related disorders.

Detection of rubella-specific immunoglobulin G: comparison of the enzyme-linked immunosorbent assay and an automated microparticle enzyme immunoassay (IMx)

An automated microparticle enzyme immunoassay (IMx Rubella IgG Antibody Assay; Abbott Laboratories, North Chicago, Ill.) was compared with a conventional enzyme-linked immunosorbent assay (ELISA) for detection of rubella-specific immunoglobulin G (IgG) in 400 consecutive antenatal patients. There was complete agreement between the two tests in this population, which had a positivity rate of 99% for rubella-specific IgG antibodies. The performance of the IMx was also evaluated at the cutoff zone by assaying 64 selected antenatal serum samples with low or negative rubella antibody titers as determined by ELISA. Overall, the IMx was found to be a specific, sensitive assay for the detection of rubella-specific IgG and is virtually fully automated for easy performance.

Detection of total antibody against hepatitis A virus by an automated microparticle enzyme immunoassay

A fully automated microparticle enzyme immunoassay, IMx HAVAB, was developed for the detection of antibody against hepatitis A virus (anti-HAV). In the IMx HAVAB assay which is run on the IMx instrument, 24 tests are completed in less than 45 minutes. IMx HAVAB sensitivity was 18–25 World Health Organization U/I and was more sensitive than the commercial RIA or EIA, HAVAB and HAVAB EIA, respectively. Specimens from blood donors, diagnostic and hospital patients and individuals with a variety of infectious and immune diseases were tested in parallel with IMx HAVAB and RIA or EIA. Overall agreement of 99.9% (2118/2121) was obtained. Prevalence of anti-HAV tested by IMx ranged from 12.3% in volunteer blood donors in St. Louis to 64.3% for hospital patients in New York City. Discordant specimens were reactive by IMx HAVAB but borderline negative by EIA or RIA, due to the better sensitivity of the IMx assay. IMx HAVAB detected both IgM and IgG subclasses of anti-HAV. Serial bleeds from six intravenous drug users with acute HAV infection were tested over 8 months for the presence of anti-HAV. At all time points, patients were strongly reactive for anti-HAV (titers > 1 1000 ). Anti-HAV titers rose during the first 20 weeks after presentation of symptoms and then declined with time.

Quantitation of hepatitis B surface antibody by an automated microparticle enzyme immunoassay

A fully automated microparticle enzyme immunoassay, IMx AUSAB, was developed for the detection and quantitation of antibody against hepatitis B surface antigen (anti-HBs). The IMx AUSAB assay can complete 24 tests in less than 45 minutes. Anti-HBs concentrations in specimens are calculated automatically by comparison of the specimen rate to values determined from a stored standard curve. IMx AUSAB sensitivity is 2—3 mIU/ml, equivalent in sensitivity to AUSAB RIA or EIA. Specimens from blood donors, diagnostic and hospital patients, hepatitis B vaccinees, and individuals with a variety of infectious and autoimmune diseases tested in parallel by IMx AUSAB and AUSAB RIA or IMx AUSAB and EIA gave overall qualitative agreement of 97.8% (1265/1293) and 99.1% (1281/1293), respectively. The prevalence of anti-HBs ranged from 5.9% in volunteer blood donors to 47.0% of specimens from a sexually transmitted disease clinic. Most discordant specimens ( 18 34 ) were low level reactive (< 10 mIU/ml) by AUSAB RIA, but negative by IMx AUSAB and AUSAB EIA. These specimens were also negative for antibodies to hepatitis B core antigen (anti-HBc). Six discordants were low level reactive by IMx but negative by RIA and EIA. Three of these six specimens were also reactive for anti-HBc suggesting that the IMx AUSAB reactivity resulted from the presence of low level anti-HBs. Quantitative agreement between IMx AUSAB and RIA or IMx and EIA for 106 specimens ranging in anti-HBs concentration from 1 to 30 000 mIU/ml gave linear correlation coefficients of 0.91 and 0.96, respectively. The IMx test was useful for monitoring hepatitis B vaccine response and seroconversion levels after hepatitis B infection.

Improvements in detection of antibody to hepatitis B core antigen by treating specimens with reducing agent in an automated microparticle enzyme immunoassay

A fully automated microparticle enzyme immunoassay (EIA), IMx Core, was developed for the detection of antibody against hepatitis B core antigen (anti-HBc). IMx Core sensitivity was less than 0.5 Paul Ehrlich Institut units per ml and was greater than that of the commercial radioimmunoassay (RIA) or EIA, Corab and Corzyme, respectively. Specimens from blood donors and diagnostic and hospital patients, which included individuals with a variety of infectious and immune diseases, were tested in parallel by the IMx Core and EIA. Overall agreement of 99.1% (4,797 of 4,841) was obtained. Prevalence of anti-HBc tested by IMx Core ranged from 1.2% in volunteer blood donors to 9.1% in hospital laboratories. Discordant specimens reactive by IMx Core but negative by Corzyme or Corab resulted from the increased sensitivity of the IMx Core assay, since other hepatitis B markers were usually present. However, most discordant specimens were positive by the EIA or RIA but negative by IMx Core. No other hepatitis B markers could be detected in these discordants, and after addition of reducing agent, these specimens also became negative by EIA or RIA. In clinical trials, 30% (14 of 47) of volunteer blood donors and 8% (9 of 119) of hospital patients testing repeatedly reactive by the EIA had reduction-sensitive (unspecific) anti-HBc reactivity. The reducing agent, dithiothreitol, was added to each specimen automatically in the IMx assay to eliminate these unspecific reactions without significantly affecting anti-HBc reactivity resulting from hepatitis B virus infection as judged by the correlation with other hepatitis B markers.