key: cord-0864857-zu1p310e
authors: Batra, Rahul; Olivieri, Luis Gonzalez; Rubin, Delfin; Vallari, Ana; Pearce, Sandra; Olivo, Ana; Prostko, John; Nebbia, Gaia; Douthwaite, Sam; Rodgers, Mary; Cloherty, Gavin
title: A Comparative Evaluation between the Abbott Panbio(TM) COVID-19 IgG/IgM Rapid Test Device and Abbott Architect(TM) SARS CoV-2 IgG Assay
date: 2020-09-16
journal: J Clin Virol
DOI: 10.1016/j.jcv.2020.104645
sha: 05d3f11d15ea1e58ff44ea2fb7bee13829067b96
doc_id: 864857
cord_uid: zu1p310e

INTRODUCTION: Antibodies to SARS-CoV-2 serve as critical diagnostic markers for determining how broadly the COVID-19 pandemic has spread, confirming patient recovery, monitoring potential long-term effects of infection, and evaluating potential protection from reinfection. As new antibody tests become available, it is important to evaluate their performance and utility. The aim of this study was to compare the performance of the Abbott PanbioTM COVID-19 IgG/IgM Rapid Test Device against the Abbott ArchitectTM SARS CoV-2 IgG Assay for the detection of the COVID-19 IgG antibody. METHODS: Two panels of specimens were utilized to challenge both antibody tests: (1) a set of 150 prepandemic negative specimens collected in 2014, and (2) a set of 122 specimens from 87 hospitalized COVID-19 patients in the US and UK that were confirmed with a positive SARS-CoV-2 RNA test result. RESULTS: The ArchitectTM test had a specificity of 100% and sensitivity of 99.1% and 93.9% when excluding or including immunocompromised patients, respectively for specimens collected >14 days post symptom onset or >5 days post-RNA testing. The PanbioTM test had 99.3% agreement to ArchitectTM. Notably, N = 6 immune-compromised individuals were identified that did not develop detectable antibodies by day 30. CONCLUSION: There is good concordance between the ArchitectTM SARS CoV-2 IgG Assay and PanbioTM COVID-19 IgG/IgM Rapid Test Device for the detection of SARS CoV-2 IgG.

Highly accurate antibody tests are urgently needed to combat the SARS-CoV-2 pandemic that has already claimed >500,000 lives worldwide 1 . Antibody tests are valuable tools that can be applied to advance our understanding of the immune response to SARS-CoV-2, estimate the scope of the COVID-19 pandemic, and appropriately manage patient care as we continue to learn more about the long-term impact of COVID-19 on recovered patients. For antibody tests to effectively meet these needs, they must be highly accurate. Therefore, it is important to challenge antibody tests with clinical specimens to evaluate their performance.

Initial studies have utilized antibody tests to monitor the immune response to SARS-CoV-2 in hospitalized patients. IgM and IgG seroconversion occurred within 10-12 days and 12-14 days respectively after the onset of symptoms 2, 4, 5, 6 . IgM levels begin to decline by week 5 and almost disappear after week 7 whereas IgG levels persist beyond week 7 7 . When serology markers were compared to RNA detection, a higher positivity rate was observed using IgM ELISA compared to quantitative PCR after 5.5 days of illness onset 3 .

With little to no gap between initial detection of IgG and IgM antibodies and a clear loss of IgM within approximately 5 weeks, IgG may serve as the primary and most persistent serological marker with the longest duration and may offer some immunity 22 .

IgG testing needs are unique to each setting. In places where high throughput and detection of multiple diagnostic markers are important, core laboratory instruments will be suitable. The EUA-approved and CE-marked Abbott Architect TM SARS-CoV-2 IgG assay (Architect TM ) is the gold standard for COVID-19 antibody testing and has been used to monitor seroprevalence in several recent studies 9,10,11 . However, worldwide access to core lab diagnostic tests has not been equal and has been especially lacking in lowand middle-income countries (LMICs) 8 where there are few laboratory facilities to perform large scale molecular and serological testing. Lateral-flow point-of-care tests that can provide results within 30 minutes with a minimal need for additional supplies or instrumentation would be ideal to confirm COVID-19 infections in these countries. The Abbott Panbio TM COVID-19 IgG/IgM Rapid Test Device (Panbio TM ) is ideally suited to meet this unmet global need because it is a rapid antibody detection lateral flow test that is simple to use, requires a small drop of whole blood or serum and produces a result in 10-20 minutes.

However, the accuracy of Panbio TM must be evaluated to determine whether it is a suitable alternative to core laboratory tests. In this study, the performance of the Abbott Panbio TM was compared to the Abbott Architect TM SARS-CoV-2 IgG EUA approved assay to address this question.

Two panels of specimens were utilized to challenge both antibody tests: (1) a set of 150 prepandemic negative specimens collected in 2014, and (2) a set of 122 specimens from 87 hospitalized COVID-19 patients in the US and UK that were confirmed with a positive SARS-CoV-2 RNA test result. The samples were collected under informed consent and were obtained from three sources as shown in Table 1 .

The samples from Guys' and St. Thomas' Hospital, London, UK (hereafter referred to as the UK cohort) were from hospitalized patients >14-days post-onset of symptoms and were confirmed positive for SARS-CoV-2 RNA with the AusDiagnostics SARS-CoV-2 test (175 copies/mL limit of detection for SARS CoV-2b) 25 . The samples from Discovery Life Sciences, Huntsville, Alabama (hereafter referred to as the US cohort) were from 5 hospitalized patients 66-77 years of age who tested positive with the Abbott RealTime SARS-CoV-2 EUA approved RNA test (100 copies/mL limit of detection for SARS CoV-2) 26 . The samples from the Gulf Coast Regional Blood Center, Houston, Texas (hereafter referred to as the Gulf Coast cohort) were collected in 2014 and were presumed negative for SARS CoV-2.

The specimens were tested on the Panbio TM and Architect TM according to the package inserts.

Both the Panbio TM and Architect TM assays detect IgG against the SARS-CoV-2 nucleocapsid (N) protein.

For Panbio TM testing, the serum and plasma samples were mixed by low speed vortexing after which 10 L was applied to the specimen well of the test device. Then, 2 drops (approximately 60 L) of buffer was added to the specimen well and a timer was started. The test device was read between 10 and 20 minutes after the start of the test. A valid result consisted of the appearance of a red line in the C (Control) area of the reading window. A negative result consisted of only the red line in the C area of the reading window. The presence of a red line in the C and G (IgG) areas of the reading window indicated a valid result for the presence of IgG. Since this study was performed to determine the presence of IgG, results appearing in the M (IgM) area of the reading window were not evaluated.

A comparative evaluation between the Panbio TM and the Architect TM was conducted to determine specificity, sensitivity, and concordance with the same panels of samples. Table 2 ). The complete concordance between the two tests with these samples indicates similar performance for detecting seroconversion for both Architect TM and Panbio TM .

Sensitivity was further evaluated with the UK panel of single timepoint collections from 82 hospitalized patients between 14-56 days post symptom onset. Testing of these samples on the Architect TM and Panbio TM was performed on the same day. Amongst these, six of the samples tested negative by both the Architect TM and Panbio TM collected on days 15-38 post onset of symptoms. A review of the medical histories for these patients revealed that 5 of 6 suffered from immune disorders or were taking immunesuppressive medications (Table 4) . Thus, the low IgG levels in these patients can be attributed to underlying conditions affecting the immune system. The Architect TM assay had a sensitivity of 100% Table 3 .

The medical histories of 6 the immunosuppressed patients from the UK cohort are shown in Table 4 .

Lastly, the overall concordance between the two tests for all specimens in the study was determined to be 99.3% (270/272), with one Architect TM negative and one Architect TM positive sample having discordant results with Panbio TM , as shown in Table 5 .

This study was performed to compare the performance of the Abbott Panbio TM COVID-19 IgG/IgM Rapid Test Device against the gold-standard Abbott Architect TM SARS CoV-2 IgG Assay for the detection of the COVID-19 IgG antibody. We report an overall percent agreement of 99.3% between Architect TM and Panbio TM . In patients that were >14 days post symptom onset or >5 days post RNA-positive, the sensitivity was 100% (76/76) and 92.6% (76/82) when the immunosuppressed patients were excluded and included in the analysis, respectively, for Architect TM . For the Panbio TM assay, the equivalent sensitivities were 98.7% (75/76) and 91.5% (75/82). The specificity was 100% (150/150) for Architect TM and 99.3% (149/150) for Panbio TM . These sensitivity and specificity rates for Architect TM are similar to those reported in other recent studies 9, 11 . The observed sensitivity for Panbio TM (92.7%) was higher compared to other lateral flow tests (55-70%), whereas the specificity for Panbio TM (99.3%) was similar to those evaluated in a recent study (95-100) 12 . The sensitivity and specificity of serology tests are critical to enable proper patient J o u r n a l P r e -p r o o f management. A recent validation study determined the Architect TM assay to have 100.0% sensitivity and 93.9% specificity 32 . The same study determined the positive percent agreement and negative percent agreement to be 100.0% and 99.6%, respectively.

The discordant results are shown in Table 6 . For both results, the Architect TM test result is considered correct.

Discordant sample #1 was positive by Architect TM (S/C = 4.51) which is well above the threshold S/C value of 1.40. The false negative rate for the Panbio TM is 0.9% (1/108). Discordant sample #2 was negative by Architect TM (S/C = 0.07) but was determined to be positive by the Panbio TM . Since the sample was collected in 2014 several years before the emergence of COVID-19, the positive result is likely due to crossreactivity between the sample and the components of the Panbio TM assay. The false positive rate for the Panbio TM COVID-19 IgG/IgM Rapid Test Device is 0.6% (1/164). A limitation of the present study was that only serum and plasma samples were tested, whereas whole blood samples were not. While it has already been established that the Panbio TM test is compatible with fingerstick whole blood, venous whole blood, serum and plasma 33 , and the Architect TM test is also compatible with venous whole blood, serum and plasma 34 , future studies will be necessary to compare the concordance between the two tests for fingerstick whole blood against venous whole blood.

In the UK cohort, 6 of the 82 patient samples that were RT-PCR positive were IgG-negative when tested with both the Architect TM and Panbio TM assays. A review of their medical histories revealed that 5 of these 6 patients were either immunocompromised, had auto-immune disease, or were on immunosuppressants. Delayed or completely absent seroconversion in immunocompromised COVID-19 patients has been previously reported 11 . Delayed antibody responses to other virus-borne diseases such as Hepatitis B and West Nile has been shown in immunosuppressed patients 14, 15 . Samples from these patients who were RT-PCR positive but IgG negative can be attributed to low levels of antibody production that were below the detection limits of the Architect TM and Panbio TM assays.

The seroconversion profiles of the UK and US cohorts is consistent with other reports. For the UK cohort, all 76 patients who were not amongst the immunocompromised group seroconverted after day 14 of symptom onset which is consistent with other recent reports of IgG seroconversion seen in the second week after symptom onset 16, 19 . For the US cohort, IgG-seroconversion was seen in all patients >5 days after being determined to be RT-PCR positive, consistent with other reports of the number of days from a positive RT-PCR result to IgG presentation 18 .

While RNA testing is important for the initial detection of infection, RT-PCR testing has limitations including difficulties in sampling, technique-dependent variability of results, and decline in RNA levels within days after the initial infection 17, 20 . The variability in symptoms can also lead to delays in RT-PCR testing especially in asymptomatic patients 24 . Since IgG levels have been shown to persist beyond 7 weeks after symptom onset, a positive antibody test is a longer-term marker of infection 21 . Antibody testing offers an alternative for patient management when RT-PCR results are not available and can serve as a secondary confirmation of infection for patients with a positive or inconclusive RT-PCR result 8 . In particular, the Panbio TM test can play a critical role in monitoring long-term antibody response to SARS-CoV-2 especially in settings that lack laboratory facilities to perform large scale molecular and serological testing, whereas the Architect TM test is a high-throughput assay that is more suitable for larger diagnostic laboratory testing. However, the utility of antibody testing is limited by the timing of each individual's immune response, and would be impacted by the potential loss of antibodies over time (i.e. seroreversion).

In addition to diagnostic uses, antibody testing is suitable for public health surveillance and vaccine development 23 . Indeed, the neutralizing antibody (nAb) response appears to be proportional to the severity of the disease 29 and the spike (S) protein is the main inducer of neutralizing antibodies 28 . A recent study showed that N is more sensitive than S for detection by antibodies: 100% for N compared to 91% for S at >14 days post symptom onset 27 . The N protein is therefore predicted to serve as a surrogate J o u r n a l P r e -p r o o f 

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