Abbott Architect Research Articles

Use of Cotton Balls in Diapers for Collection of Urine Samples Impacts the Analysis of Routine Chemistry Tests: An Evaluation of Cotton Balls, Diapers, and Chemistry Analyzers

To evaluate the suitability of urine samples collected with cotton balls placed into diapers for routine laboratory chemistry analyses. Twenty pools of residual unpreserved urine samples were separated into control and treated aliquots. The treated samples were absorbed into 2 different brands of cotton balls, wrapped in 3 different brands of diapers, and incubated at 37°C for 1hour. The urine-soaked cotton balls were placed into a syringe and expressed via plunger depression. Urine sodium, potassium, creatinine, urea, calcium, magnesium, inorganic phosphorus, albumin, and total protein were measured on all samples on 5 automated clinical chemistry platforms: Ortho Vitros 4600, Siemens Dimension Vista 500, Beckman Coulter AU5822, Roche Cobas 6000, and Abbott Architect c8000 at 5 separate hospital laboratories. Criteria used to exclude the presence of significant effects of urine from presoaked cotton balls in a diaper on the measurement of chemistry laboratory tests were R2 >0.95, slope of 0.9-1.1, and mean bias within ±10%. Albumin and total protein measurements demonstrated significant negative bias in urine from both brands of presoaked cotton balls with all brands of diapers on all 5 chemistry platforms compared with the control urine. We did not observe a significant effect of presoaking urine in cotton balls in a diaper on the measurement of sodium, inorganic phosphorus, and urea. The remaining tests demonstrated significant effects when measured in urine from presoaked cotton balls and/or diapers that were specific to the chemistry analyzer platform or diaper. Diaper and cotton ball-based urine collection significantly impacts the measurement of several common chemistry assays.

Periodic Comparability Verification and Within-Laboratory Harmonization of Clinical Chemistry Laboratory Results at a Large Healthcare Center With Multiple Instruments.

BackgroundResults from laboratories using multiple instruments should be standardized or harmonized and comparability-verified for consistent quality control. We developed a simple frequent comparability verification methodology applicable to large healthcare centers using multiple clinical chemistry instruments from different manufacturers.MethodsComparability of five clinical chemistry instruments (Beckman Coulter AU5800, Abbott Architect Ci16000, two Siemens Vista 1500, and Ortho Vitros 5600) was evaluated from 2015 to 2019 for 12 clinical chemistry measurements. Pooled residual patient samples were used for weekly verifications. Results from any instrument exceeding the allowable verification range versus the results from the comparative instrument (AU5800) were reported to clinicians after being multiplied by conversion factors that were determined via a linear regression equation obtained from simplified comparison.ResultsOver the five-year study period, 432 weekly inter-instrument comparability verification results were obtained. Approximately 58% of results were converted due to non-comparable verification. Expected average absolute percent bias and percentage of non-comparable results for non-converted and converted results after conversion action were much lower than those for data measured before conversion action. The inter-instrument CV for both non-converted and converted results after conversion action was much lower than that for measured data before conversion action for all analytes.ConclusionsWe maintained within-laboratory comparability of clinical chemistry tests from multiple instruments for five years using frequent low-labor periodic comparability verification methods from pooled residual sera. This methodology is applicable to large testing facilities using multiple instruments.

Estimating SARS-CoV-2 Seroprevalence in Canadian Blood Donors, April 2020 to March 2021: Improving Accuracy with Multiple Assays.

ABSTRACTWe have previously used composite reference standards and latent class analysis (LCA) to evaluate the performance of laboratory assays in the presence of tarnished gold standards. Here, we apply these techniques to repeated, cross-sectional study of Canadian blood donors, whose sera underwent parallel testing with four separate SARS-CoV-2 antibody assays. We designed a repeated cross-sectional design with random cross-sectional sampling of all available retention samples (n = 1500/month) for a 12 -month period from April 2020 until March 2021. Each sample was evaluated for SARS-CoV-2 IgG antibodies using four assays an Abbott Architect assay targeting the nucleocapsid antigen (Abbott-NP, Abbott, Chicago IL) and three in-house IgG ELISAs recognizing distinct recombinant viral antigens: full-length spike glycoprotein (Spike), spike glycoprotein receptor binding domain (RBD) and nucleocapsid (NP). We used two analytic approaches to estimate SAR-CoV-2 seroprevalence: a composite reference standard and LCA. Using LCA to estimate true seropositivity status based on the results of the four antibody tests, we estimated that seroprevalence increased from 0.8% (95% CI: 0.5–1.4%) in April 2020 to 6.3% (95% CI: 5.1–7.6%) in March 2021. Our study provides further support for the use of LCA in upcoming public health crises, epidemics, and pandemics when a gold standard assay may not be available or identifiable.IMPORTANCE Here, we describe an approach to estimating seroprevalence in a low prevalence setting when multiple assays are available and yet no known gold standard exists. Because serological studies identify cases through both diagnostic testing and surveillance, and otherwise silent, unrecognized infections, serological data can be used to estimate the true infection fatality ratio of a disease. However, seroprevalence studies rely on assays with imperfect sensitivity and specificity. Seroreversion (loss of antibody response) also occurs over time, and with the advent of vaccination, distinction of antibody response resulting from vaccination as opposed to antibody response due to infection has posed an additional challenge. Our approach indicates that seroprevalence on Canadian blood donors by the end of March 2021was less than 10%. Our study supports the use of latent class analysis in upcoming public health crises, epidemics, and pandemics when a gold standard assay may not be available or identifiable.

MiCheck prostate blood test for aggressive prostate cancer designed for the clinical lab setting.

229 Background: Clinicians want a more accurate diagnostic test to identify patients for prostate biopsy. We have previously described the development of a Luminex based test for aggressive prostate cancer (MiCheck). To facilitate widespread deployment of MiCheck on standard clinical chemistry analysers such as Roche Cobas and Abbott ARCHITECT/Alinity systems, we have performed additional analytical validation and model development using the MiCheck-01 clinical samples. A novel algorithm, termed MiCheck Prostate, was developed to differentiate aggressive prostate cancer (Gleason 3+4 or above) from non-aggressive (GS3+3) or no cancer patients. Methods: Serum protein biomarkers were measured in 317 samples from the MiCheck-01 clinical trial using either Luminex Multiplex kits, Abbott ARCHITECT or Beckmann Coulter systems. Logistic regression models were used to select best analytes, then Monte Carlo cross-validation was applied to avoid overfitting. A final model was selected from the cross-validation models with best test specificity at 95% sensitivity. The MiCheck-01 samples were later all measured on a standard Abbott ARCHITECT system using commercial ARCHITECT IVD tests. The best cross-validated model was developed and the results compared to those obtained from the mixed analyte platforms using ROC curve analysis. Results: The MiCheck Prostate algorithm was developed to maximise discrimination between aggressive prostate cancer and no cancer or non-aggressive cancer. The MiCheck Prostate algorithm reports a percentage risk of aggressive prostate cancer on biopsy. MiCheck Prostate is a logistic regression algorithm that combines three serum protein markers and one clinical factor and was derived using data from the MiCheck-01 trial. The algorithm gave an AUC of 0.82, with a 48% specificity at a 95% sensitivity cutpoint, with a negative predictive value of 94% for GS3+4 and higher cancers. The samples were later re-measured using all ARCHITECT immunoassays. Good correlations of each analyte across different measurement platforms was observed (Pearson’s R > 0.9). The algorithm was revalidated using the new set of analyte values. AUC of 0.82 for the detection of aggressive CaP, and sensitivity of 95%, specificity of 47% were obtained for the best model, showing no statistical difference to the previous best model derived from the mixed platforms. NPV of 94% for GS3+4 or higher cancers was maintained. Conclusions: The MiCheck Prostate test shows high sensitivity, specificity and NPV for the detection of aggressive prostate cancer. It uses analytes widely available on standard clinical chemistry analysers such as Abbott Architect and Roche Cobas, hence is simple to deploy in the laboratory setting. Studies are ongoing to confirm the MiCheck Prostate algorithm performance using additional clinical sample cohorts.

Performance of the Abbott SARS-CoV-2 IgG serological assay in South African 2 patients.

In late December 2019, pneumonia cases of unknown origin were reported in Wuhan, China. This virus was named SARS-CoV2 and the clinical syndrome was named coronavirus disease 19 (COVID-19). South Africa, despite strict and early lockdown has the highest infection rate in Africa. A key component of South Africa’s response to SARSCoV2 was the rapid scale-up of diagnostic testing. The Abbott SARS-CoV2 assay detects IgG antibodies against the Nucleocapsid (N) protein of the SARS-CoV2 virus. This study undertook to validate and evaluate performance criteria of the Abbott assay and to establish whether this assay would show clinical utility in our population. Positive patients (n = 391) and negative controls (n = 139) were included. The Architect-i and Alinity-i systems were analyzers that were used to perform the SARS-CoV-2 IgG assay. In-house ELISA was incorporated into the study as a confirmatory serology test. A total of number of 530 participants was tested, 87% were symptomatic with infection and 13% were asymptomatic. When compared to RT-qPCR, the sensitivity of Architect and Alinity SARS-CoV2 assays was 69.5% and 64.8%, respectively. Specificity for Architect and Alinity assays was 95% and 90.3%, respectively. The Abbott assay was also compared to in house ELISA assay, with sensitivity for the Architect and Alinity assays of 94.7% and 92.5%, respectively. Specificity for Abbott Alinity assays was 91.7% higher than Abbott Architect 88.1%. Based on the current findings testing of IgG after 14 days is recommended in South Africa and supports other studies performed around the world.

The Second Shot of CoronaVac Vaccine May Cause Reduction of Antibody Levels in People who Previously had COVID-19

The CoronaVac vaccine is an inactivated type two-dose regimen vaccine developed and manufactured by Sinovac Life Sciences Company, in China. It has already been used in China's vaccination program, while 21 other countries (including Indonesia, Turkey and Brazil) also granted emergency use authorization for this vaccine. In Turkey, on January 14, 2021, healthcare workers (HCWs) started to be vaccinated with CoronaVac as the priority group in vaccination. An important question that arose at this time was about how the vaccination schedule would be for people who had previously had Coronavirus disease 2019 (COVID-19). The Centers for Disease Control and Prevention (CDC) recommends that those who have had a previous COVID-19 infection can be vaccinated regardless of their previous infection. CDC guidelines also mention that "…if antibody (Ab) testing was done after the first dose of an mRNA vaccine, the vaccination series should be completed regardless of the Ab test result". It should be noted here that this statement applies particularly to mRNA type vaccines, whereas CoronaVac jab is an inactivated type two-dose regimen vaccine. The aim of this study was to present interim results of our ongoing study to compare the effect of two doses of inactivated CoronaVac vaccine on humoral immunity of people who had previously severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection, and those people who did not have the infection. In our study, CoronaVac jab containing 600 SU inactivated SARS-CoV-2 antigen was administered as 0.5 ml to 62 HCWs in Yeditepe University Hospital (Istanbul, Turkey), in accordance with the manufacturer's recommendations. Ab levels against spike receptor binding region of SARS-CoV-2 were measured quantitatively. SARS-CoV-2 IgG assay were performed using Abbott Architect i2000 instrument (Abbott Laboratories, Abbott Park, IL, USA). Ab titers were measured before vaccination (Ab0), one month after the first vaccination (Ab1), and one month after the second vaccination (Ab2). The Ab responses of 62 HCWs before and after CoronaVac vaccination were determined. Two groups were created. Group 1 consisted of 18 females and 15 males who were tested as COVID-19 positive, previously. Group 2 consisted of 20 females and 9 males who never had the infection. Minimum, median and maximum Ab0 values of Group1 were 1.6, 180.8 and 5582.6, respectively and Ab1 values were 26.3, 1005.7 and 3923.1; Ab2 values were 202.1, 1119.1 and 2885.9, (in au/mL) respectively. On the other hand, minimum, median and maximum Ab0 values of Group 2 were 0.1, 1.8, and 37.2, Ab1 values were 4.7, 72.7, 470.2, and Ab2 values were 270.3, 746.2 and 5554.1, respectively. In Group 1, 20 of the HCWs showed lower Ab2 titers, while 13 of the HCWs showed higher Ab2 titers than the Ab1 titers. Whereas in Group2 all HCWs had higher Ab2 titers than the Ab1 titers. When the increasing and decreasing Ab2 titers of both groups were evaluated with the 2×2 contingency table and Fisher's exact chi-square test, a statistically significant difference was found between the groups (p<0.001). As a result, we think that a single dose of CoronaVac vaccine similarly to mRNA vaccines can be administered to people who have had COVID-19 due to the possibility that the Ab levels measured after the first dose of vaccine will decrease after the second dose of vaccine.

Seroprevalence of COVID-19 IgG Antibody in Resident and Fellow Physicians in Milwaukee, Wisconsin: Analysis of a Cross-Sectional Survey.

Medical trainees are likely at differential risk of exposure to COVID-19 per respective clinical activity. We sought to determine the seroprevalence of COVID-19 antibody (Ab) among resident and fellow physicians with varying degrees of exposure to COVID-19. A cross-sectional study of Milwaukee-based resident and fellow physicians, encompassing December 2019-June 2020, was conducted. Relevant variables of interest were ascertained by survey and payroll data, and Abbott ARCHITECT Ab test (index cut-off of ≥1.4) was performed. Descriptive statistics were generated, with 95% CI calculated for the study's primary outcome of seroprevalence. Among survey respondents (92 of 148, 62%), 61% were male, 44% were non-White, mean age was 31 years, 94% had no underlying conditions, and 52% were either family or internal medicine residents. During the study period, ≥32% reported cough, headache, or sore throat and 62% traveled outside of Wisconsin. Overall, 83% thought they had a COVID-19 exposure at work and 33% outside of work; 100% expressed any exposure. Of those exposed at work, 56% received COVID-19 pay, variously receiving 69 mean hours (range: 0-452). Ultimately, 82% (75 of 92) had an Ab test completed; 1 individual (1.3%; 95% CI: 0.0-3.9) tested seropositive, was not previously diagnosed, and had received COVID-19 pay. The low Ab seroprevalence found in resident and fellow physicians was similar to the concurrently reported 3.7% Ab-positive rate among 2456 Milwaukee-based staff in the same integrated health system. Ultimately, COVID-19 seroconversion may be nominal in properly protected resident and fellow physicians despite known potential exposures.

SARS-CoV-2 seroprevalence in Portugal following the third epidemic wave: results of the second National Serological Survey (ISN2COVID-19)

Background Integrated approaches to surveillance of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection are important for public health actions. The 2nd National Serological Survey (ISN2COVID-19) aimed to characterize the extent of SARS-CoV-2 infection and vaccine-induced response in the Portuguese population following the third epidemic wave and the launch of the vaccination campaign. Methods A cross-sectional study was performed using data on 8463 Portuguese 1–79 years of age, collected in February and March, 2021. SARS-CoV-2 IgM and IgG (anti-nucleoprotein and anti-spike) antibodies were determined in serum samples using Abbott Architect chemiluminescent microparticle assays. Post-infection and vaccine-induced seroprevalence with 95% confidence intervals (95%CI) were estimated in the overall sample and stratified by population characteristics. Results The estimated seroprevalence was 15.5% (95%CI:14.6–16.5%), of which 13.5% (95%CI: 12.6–14.4%) was attributable to natural infection and 2.0% (95%CI:1.7–2.4%) to vaccination. The lowest seroprevelence was observed in persons aged 70–79 years (8.9% 95%CI:6.8–11.6), while seroprevalence in children (14.3%; 95%CI:11.5–17.6%) and adolescents (12.9%; 95%CI:10.5–15.7%) was similar to that of persons aged between 20 and 69 years. Of seropositive individuals, 22.6% (95%CI:19.7–25.9%) did not report any symptoms in 6 months prior to interview. Of persons with completed vaccination (2-doses), 98.6% (95%CI: 93.0–99.7%) had specific IgG (anti-S) antibodies. Conclusions After the third epidemic wave, the post-infection SARS-CoV-2 seroprevalence was 1.7 times higher than the cumulative incidence based on PCR-testing, but was higher (2.7 times) in children may be due to the high proportion of asymptomatic and mild infections.

Insights into Preservation of Blood Biomarkers in Biobank Samples.

Insights into Preservation of Blood Biomarkers in Biobank Samples.

CLINICIANS DILEMMA: FALSELY UNDETECTED TSH LEVELS DUE TO TSH ISOFORM ON POPULAR COMMERCIAL IMMUNOASSAY IN INDIAN SUBJECT AND RETROSPECTIVE ANALYSIS

Introduction: TSH is one of the most routinely measured tests the clinical laboratory to diagnose and monitor thyroid diseases. TSH as the preferred screening test as recommended by The American Thyroid Association and the American Association of Clinical Endocrinologists for diagnosing thyroid dysfunction. Third-generation Ultra serum TSH assays have a functional sensitivity of 0.001 uIU/mL and have been considered highest among biochemical assay for assessing thyroid disorders. However, as observed in many clinical laboratories sometimes results of TSH assays are discordant among different immunoassay platforms.&#x0D; Case Report: TSH values of a 56 years old male on Siemens Attelica while TSH was found to be elevated on Abbott Architect 1000 and Beckman Coulter DXI800. Retrospective analysis revealed few other cases (8/190) approx. 4.2 % showed discordant TSH values. This was found to be possibly because of mutation in TSH beta region (R55G).&#x0D; Conclusion: Our present study suggest that these individuals who shows &lt;0.001 values on Siemens Attelica must be tested with other platforms to assure appropriate management of disease. Further, clinicians and laboratory staff need to be aware about TSH variants along with other reported interferences.

Seroprevalence of SARS-CoV-2 antibodies in vaccinated healthcare workers in Marrakech (Morocco).

IntroductionThe SARS-CoV-2 pandemic has had a considerable impact, causing millions of deaths worldwide, including many healthcare workers (HCWs). The pharmaceutical industry has been working diligently since the start of the pandemic to develop various vaccines to fight the spread of the virus and protect the population.ObjectiveTo study the seroprevalence of neutralizing anti-SARS-CoV-2 antibodies in vaccinated HCWs at the Mohamed VI University Hospital in Marrakech and to determine the parameters that can influence immune response.MethodsA cross-sectional study of 138 HCWs was performed between October and December 2021 by measuring IgG antibodies directed against the spike antigen of SARS-CoV-2 using an Abbott Architect® SARS-CoV-2 IgG II assay.ResultsThe mean age was 31.42 years, the sex ratio was 2.94 women to each man, and the overall prevalence was 97%. We found 39.5% of the participants had experienced COVID-19 infections pre-vaccination, which decreased to 26.8% after vaccination. Neutralizing antibody titers were dependent on the type of vaccine: they were higher with the Pfizer-BioNTech vaccine, the number of doses (p < .001), and post-vaccine COVID-19 form. The post-vaccine COVID-19 infection rates were lower with the Sinopharm vaccine.ConclusionHeterologous vaccination with non-mRNA and mRNA vaccines and the consideration of post-vaccination COVID-19 infection as a booster could help optimize vaccine results while reducing potential side effects.

A comparison of antibody response in kidney transplant recipients and healthcare workers who had PCR-confirmed COVID-19 infection.

Data on antibody response following COVID-19 in kidney transplant recipients is scarce. This crosssectional study aims to investigate the antibody response to COVID-19 among kidney transplant recipients. We recruited 46 kidney transplant recipients with RT-PCR-confirmed COVID-19 and 45 recipients without COVID-19 history. We also constructed two control groups (COVID-19 positive and negative) from a historical cohort of healthcare workers. We used age and sex-based propensity score matching to select the eligible subjects to the control groups. We measured the SARS-CoV-2 IgG levels quantitatively using the Abbott ARCHITECT system. An antibody level above 1.4 S/C was defined as positivity. Transplant recipients with COVID-19 had a higher BMI, and COVID-19 history in a household member was more common than that of the transplant recipient without COVID-19. IgG seropositivity rate (69.6% vs. 78.3%, p = 0.238) and the median IgG level (3.28 [IQR: 0.80-5.85] vs. 4.59 [IQR: 1.61-6.06], p = 0.499) were similar in COVID-19-positive transplant recipients and controls. Kidney transplant recipients who had a longer duration between RT-PCR and antibody testing had lower antibody levels (r = -0.532, p < 0.001). At the early post-COVID-19 period, kidney transplant recipients have a similar antibody response to controls. However, these patients' antibody levels and immunity should be closely monitored in the long term.

An evaluation of the performance of the Point of Care Test iCHROMA™ AFP method: Precision and accuracy

The estimation of serum alpha-fetoprotein (AFP) is useful in the diagnosis and monitoring of primary hepatocellular carcinoma, hepatoblastoma, non-seminomatous testicular germ cell tumours and other germ cell tumours. The iCHROMA™ AFP is a lateral flow chromatography, fluorescence immunoassay (FIA) for the quantitative determination of AFP in serum or plasma. In this study, the Boditech iCHROMA™ AFP assay had a very good precision of 9.8%. It showed a very good correlation with the following 12 methods: Abbott Architect (r2 = 0.9705), BioMerieux VIDAS (r2 = 0.9717), Roche Cobas 6000/8000 (r2 = 0.9738), Siemens Centaur XP/XPT/Classic (r2 = 0.9654), Siemens/DPC/Immulite 2000/2500 (r2 = 0.9673), Siemens/DPC/Immulite 1000 (r2 = 0.9670), Beckman Dxl 600/800 (r2 = 0.9676), Roche Elecsys (r2 = 0.9683), Roche Cobas 4000/e411 (r2 = 0.9688), Roche Modular E170 (r2 = 0.9692), SNIBE Maglumi (r2 = 0.9457) and Ortho Vitros 3600/5600/ECi (r2 = 0.9714). In summary, the iCHROMA™ AFP, a rapid point of care test method, has a within-run precision value of less than 10% and excellent correlations with traditional laboratory methods. There is a consistent overestimation with the iCHROMA™ method, which must be taken into consideration when setting a reference range.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody lateral flow assay for antibody prevalence studies following vaccination: a diagnostic accuracy study.

Background: Lateral flow immunoassays (LFIAs) are able to achieve affordable, large scale antibody testing and provide rapid results without the support of central laboratories. As part of the development of the REACT programme extensive evaluation of LFIA performance was undertaken with individuals following natural infection. Here we assess the performance of the selected LFIA to detect antibody responses in individuals who have received at least one dose of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine. Methods: This was a prospective diagnostic accuracy study. Sampling was carried out at renal outpatient clinic and healthcare worker testing sites at Imperial College London NHS Trust. Two cohorts of patients were recruited; the first was a cohort of 108 renal transplant patients attending clinic following two doses of SARS-CoV-2 vaccine, the second cohort comprised 40 healthcare workers attending for first SARS-CoV-2 vaccination and subsequent follow up. During the participants visit, finger-prick blood samples were analysed on LFIA device, while paired venous sampling was sent for serological assessment of antibodies to the spike protein (anti-S) antibodies. Anti-S IgG was detected using the Abbott Architect SARS-CoV-2 IgG Quant II CMIA. A total of 186 paired samples were collected. The accuracy of Fortress LFIA in detecting IgG antibodies to SARS-CoV-2 compared to anti-spike protein detection on Abbott Assay Results: The LFIA had an estimated sensitivity of 92.0% (114/124; 95% confidence interval [CI] 85.7% to 96.1%) and specificity of 93.6% (58/62; 95% CI 84.3% to 98.2%) using the Abbott assay as reference standard (using the threshold for positivity of 7.10 BAU/ml) Conclusions: Fortress LFIA performs well in the detection of antibody responses for intended purpose of population level surveillance but does not meet criteria for individual testing.

Prevalence and duration of detectable SARS-CoV-2 nucleocapsid antibodies in staff and residents of long-term care facilities over the first year of the pandemic (VIVALDI study): prospective cohort study in England

SummaryBackgroundLong-term care facilities (LTCFs) have reported high SARS-CoV-2 infection rates and related mortality, but the proportion of infected people among those who have survived, and duration of the antibody response to natural infection, is unknown. We determined the prevalence and stability of nucleocapsid antibodies (the standard assay for detection of previous infection) in staff and residents in LTCFs in England.MethodsThis was a prospective cohort study of residents 65 years or older and of staff 65 years or younger in 201 LTCFs in England between March 1, 2020, and May 7, 2021. Participants were linked to a unique pseudo-identifier based on their UK National Health Service identification number. Serial blood samples were tested for IgG antibodies against SARS-CoV-2 nucleocapsid protein using the Abbott ARCHITECT i-system (Abbott, Maidenhead, UK) immunoassay. Primary endpoints were prevalence and cumulative incidence of antibody positivity, which were weighted to the LTCF population. Incidence rate of loss of antibodies (seroreversion) was estimated from Kaplan-Meier curves.Findings9488 samples were included, 8636 (91·0%) of which could be individually linked to 1434 residents and 3288 staff members. The cumulative incidence of nucleocapsid seropositivity was 34·6% (29·6–40·0) in residents and 26·1% (23·0–29·5) in staff over 11 months. 239 (38·6%) residents and 503 women (81·3%) were included in the antibody-waning analysis, and median follow-up was 149 days (IQR 107–169). The incidence rate of seroreversion was 2·1 per 1000 person-days at risk, and median time to reversion was 242·5 days.InterpretationAt least a quarter of staff and a third of surviving residents were infected with SAR-CoV-2 during the first two waves of the pandemic in England. Nucleocapsid-specific antibodies often become undetectable within the first year following infection, which is likely to lead to marked underestimation of the true proportion of people with previous infection. Given that natural infection might act to boost vaccine responses, better assays to identify natural infection should be developed.FundingUK Government Department of Health and Social Care.

Preserved C‐peptide in survivors of COVID‐19: Post hoc analysis

Preserved <scp>C</scp>‐peptide in survivors of <scp>COVID</scp>‐19: Post hoc analysis

Comparison of serum indices results on some biochemical analysers

Objective: To identify hemolysis, icterus, lipemia (HIL) indices measurement on four clinical chemistry analyzers: Abbott Architect C8000 (AA), Roche Cobas C501 (RC), Beckman Coulter AU5800 (BC), Siemens Advia 1800 (SA). Subject and method: Plasma of patients were examined at 108 Military Central Hospital (108 MCH) from 12/2020 to 04/2021, comprising of 240ml normal plasma sample, 30ml artificial hemolyzed plasma for H index, 30ml icteric plasma with 360μmol/L total bilirubin, 30ml plasma with 1g/L of Intralipid 20% for lipemia. A cross-sectional study was conducted to compare results of HIL indices on 4 analyzers Abbott Architect C8000 (AA), Roche Cobas c501 (RC), Beckman Coulter AU5800 (BC), Siemens Advia 1800 (SA). Result: The agreement of H index among 4 instruments was good, and values of I index on the AA, SA, RC were absolutely suitable (kappa 0.75 - 1.0). Nevertheless, the comparability between results of I index on the BC and 3 others platforms was mediate (kappa 0.53 - 0.55) while I index on the RC, SA, AA was extremely suitable (kappa 1.0). Even though, the agreement of L index between BC and SA was not acceptable (kappa &lt; 0.2), it was comparable on the remaining analyzers (kappa 0.55 - 0.933). Conclusion: There was comparability of HIL indices among 4 analyzers except L index between the BC and SA. Specifically, the results of all HIL indices on the SA, RC, AA analyzers were high agreement.

LB9. Longitudinal antibody dynamics in children infected with SARS-CoV-2 through 6 months post-infection

BackgroundSevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection elicits antibodies (Abs) that bind several viral proteins such as the spike entry protein and the abundant nucleocapsid (N) protein. We examined convalescent sera collected through 6 months (~24wks) post-SARS-CoV-2 infection in children to evaluate changes in neutralization potency and N-binding.MethodsOutpatient, hospitalized, and community recruited volunteers < 18 years with COVID-19 were enrolled in a longitudinal study at Seattle Children’s Hospital. Analysis includes symptomatic and asymptomatic children with laboratory-confirmed SARS-CoV-2 infection who provided blood samples at approximately 4wks (range: 2-18wks, IQR:4-8wks) and 24 wks (range: 23-35wks, IQR:25-27wks) after diagnosis. We measured neutralizing Ab using an in-house pseudoneutralization assay and anti-N binding Ab using the Abbott Architect assay.ResultsOf 32 children enrolled between April 2020 and January 2021, 27 had no underlying immunocompromised state and 25 of these 27 children had symptomatic disease. Ten of 27 had a > 2-fold decrease neutralization titers between 4 and 24wks (most were < 10-fold); 12 had < 2-fold change; and 5 had neutralization titers that increased > 2-fold over time (Fig. 1A). All but one of these 27 children had detectable neutralizing activity at 24wks. Anti-N Abs were assessed for 25 children at 4wks and 17 children at 24wks (data pending for 14 samples); all children with paired samples had a > 1.75-fold Abbott index reduction at 24wks, and 5 children had no detectable anti-N Abs by 24wks (Fig. 2A). An additional 5 children with symptomatic disease had complicating immunosuppression or multiple blood transfusions; 2 had decreasing neutralizing titers, 2 increased, and 1 had no change (Fig. 1B). Anti-N Abs were undetectable for one child by 24wks (data pending for 4 samples) (Fig. 2B). No participants received COVID-19 vaccine.Figure 1. Pseusoneutralization titers in children over time. Figure 2. Nucleocapsid-binding antibody titers in children over time. ConclusionWe show neutralizing Abs wane to a small degree over 24wks post-SARS-CoV-2 infection and remain detectable in most children. In contrast, anti-N Abs decreased, becoming undetectable in some children by 24wks. These findings add to understanding of the natural history of SARS-CoV-2 immunity in children.* This study was supported by CDC BAA75D301-20-R-67897Disclosures Jesse Bloom, PhD, Flagship Labs 77 (Consultant)Moderna (Consultant) Janet A. Englund, MD, AstraZeneca (Consultant, Grant/Research Support)GlaxoSmithKline (Research Grant or Support)Meissa Vaccines (Consultant)Pfizer (Research Grant or Support)Sanofi Pasteur (Consultant)Teva Pharmaceuticals (Consultant)

489. SARS-CoV-2 Seroprevalence and Antibody Response Among Pregnant People in Seattle, WA

BackgroundAntenatal care is a unique opportunity to assess SARS-CoV-2 seroprevalence and antibody response in pregnant people, including those with previously unknown infection. MethodsPregnant people were screened for SARS-CoV-2 IgG during antenatal care or delivery in Seattle, Washington with Abbott Architect chemiluminescent immunoassay which provides quantitative index (positive ≥1.4). Participants with IgG+ results or identified with RT-PCR+ results via medical records were invited to enroll in a longitudinal evaluation of antibody responses. We report preliminary results of an ongoing seroprevalence and longitudinal study with planned 18-month follow-up.ResultsBetween September 9, 2020–May 7, 2021, we screened 1304 pregnant people; 62 (4.8%) tested SARS-CoV-2 IgG+, including 28 (45%) with known prior SARS-CoV-2 infection. Among participants testing IgG+, median age was 32 years (interquartile range [IQR] 26–35) and median gestational age was 21 weeks (IQR 12–38) at screening; median IgG index was 3.2 (IQR 2.1–4.9, range 1.4–9.9), including 3.9 (IQR 2.3–5.8) among those with vs. 2.7 (IQR 1.9–4.2) among those without prior RT-PCR+ results (p=0.05 by Wilcoxon rank-sum). Of 30 longitudinal study participants enrolled, 24 tested IgG+ at baseline (75% with prior RT-PCR+ result) and 6 tested IgG- on enrollment but were identified as previously RT-PCR+ via medical records; 24/30 (80%) reported previous symptoms. Of 24 participants testing IgG+ at baseline, 14 (58%) had first follow-up IgG results at median of 66 days (IQR 42–104) since initial testing, with median IgG index of 2.0 (IQR 1.0–3.8). 9/14 (64%) participants with repeat IgG testing remained IgG+ at first follow-up (≤280 days after first RT-PCR+ result for those with and ≥104 days after first IgG detection for those without prior RT-PCR+ results), while 5/14 (26%) had a negative Abbott IgG test at a median of 81 days (IQR 75–112) since initial testing. ConclusionNearly half of pregnant people testing SARS-CoV-2 IgG+ reported no known prior SARS-CoV-2 diagnosis or symptoms. SARS-CoV-2 IgG antibody response and durability in pregnancy has implications for maternal and neonatal protection and susceptibility and highlights potential benefits of vaccination in this population.Disclosures Sylvia LaCourse, MD, Merck (Grant/Research Support) Alisa Kachikis, MD, MS, GlaxoSmithKline (Consultant)Pfizer (Consultant) Alexander L. Greninger, MD, PhD, Abbott (Grant/Research Support)Gilead (Grant/Research Support)Merck (Grant/Research Support) Janet A. Englund, MD, AstraZeneca (Consultant, Grant/Research Support)GlaxoSmithKline (Research Grant or Support)Meissa Vaccines (Consultant)Pfizer (Research Grant or Support)Sanofi Pasteur (Consultant)Teva Pharmaceuticals (Consultant) Alison Drake, PhD, MPH, Merck (Grant/Research Support)

The Study to Investigate COVID-19 Infection in People Living in Ireland (SCOPI): A seroprevalence study, June to July 2020.

BackgroundRobust data on SARS-CoV-2 population seroprevalence supplement surveillance data in providing evidence for public health action.AimTo conduct a SARS-CoV-2 population-based seroprevalence survey in Ireland.MethodsUsing a cross-sectional study design, we selected population samples from individuals aged 12–69 years in counties Dublin and Sligo using the Health Service Executive Primary Care Reimbursement Service database as a sampling frame. Samples were selected with probability proportional to the general population age–sex distribution, and by simple random sampling within age–sex strata. Antibodies to SARS-CoV-2 were detected using the Abbott Architect SARS-CoV-2 IgG Assay and confirmed using the Wantai Assay. We estimated the population SARS-CoV-2 seroprevalence weighted for age, sex and geographic area.ResultsParticipation rates were 30% (913/3,043) and 44% (820/1,863) in Dublin and Sligo. Thirty-three specimens had detectable SARS-CoV-2 antibodies (1.9%). We estimated weighted seroprevalences of 3.12% (95% confidence interval (CI): 2.05–4.53) and 0.58% (95% CI: 0.18–1.38) for Dublin and Sligo, and 1.69% (95% CI: 1.13–2.41) nationally. This equates to an estimated 59,482 (95% CI: 39,772–85,176) people aged 12–69 years nationally having had infection with SARS-CoV-2, 3.0 (95% CI: 2.0–4.3) times higher than confirmed notifications. Ten participants reported a previous laboratory-confirmed SARS-CoV-2 -infection; eight of these were antibody-positive. Twenty-five antibody-positive participants had not reported previous laboratory-confirmed infection.ConclusionThe majority of people in Ireland are unlikely to have been infected with SARS-CoV-2 by June–July 2020. Non-pharmaceutical public health measures remained key pending widespread availability of vaccination, and effective treatments.