PRO-LAB DIAGNOSTICS IS PLEASED TO ANNOUNCE THE LAUNCH OF A RAPID ANTIBODY TEST FOR SARS-CoV-2

As the UK begins to move out of lockdown, significant efforts are being made to protect public health and prevent local, regional or national spikes in cases. It is widely understood that antibody testing is a useful tool for determining population seroconversion and may aid epidemiological and public health decisions.

In addition to the Viasure® Real-Time PCR kit, used widely in the UK, we are very pleased to be launching another tool to help laboratory and medical colleagues continue the fight against COVID-19.

The OnSite® COVID-19 IgG/IgM Rapid Test is a single use lateral flow immunoassay intended for qualitative detection and differentiation of anti-SARS-CoV-2 IgG and IgM antibodies in 10 minutes, from human serum and plasma or whole blood.Resulting from a partnership between CTK Biotech, Avonchem and Pro-Lab Diagnostics, the kit was launched in early March and has undergone extensive evaluation.

Read on for full technical details, evaluation reports and performance data…

Performance Data

Positive Agreement

Endemic; subjects symptomatic or with suspected Infection. A total of 210 specimens (serum or plasma) were collected during the COVID-19 pandemic from subjects either symptomatic or with a suspected infection. All subjects were confirmed COVID-19 positive by real time PCR (RT-PCR). Positive agreement for all subjects is shown in the table below.

Negative Agreement

Endemic; subjects symptomatic or with suspected Infection. A total of 270 specimens (serum or plasma) were collected during the COVID-19 pandemic from subjects either symptomatic or with a suspected infection. All subjects were confirmed COVID-19 negative by real time PCR. Negative agreement for all subjects is shown in the table below:

Cross-reactivity

No false positive test results for either anti-SARS-CoV-2 virus IgG and IgM were observed on 5-12 specimens from the following disease states or specific conditions:

Class Specificity

Recombinant human anti-SARS-CoV-2 IgG and IgM antibodies were serially-diluted in COVID-19 negative plasma and tested on the OnSite® COVID- 19 IgG/IgM Rapid Test. No cross-reactivity between COVID-19 IgG and IgM was observed, as shown in the following table:

The results from the class specificity study above also suggest no hook effect in the OnSite® COVID-19 IgG/IgM Rapid Test, as no negative impact was observed when testing samples with increased concentration of either IgG or IgM antibodies.

Matrix equivalency

The performance of the OnSite® COVID-19 IgG/IgM Rapid Test in different specimen matrices was evaluated in samples from 13 convalescent confirmed positive COVID-19 and from 14 COVID-19 negative subjects. Capillary whole blood was collected by finger stick puncture and 5 different venous matrices where collected by venepuncture: venous whole blood, serum, and 3 plasma matrices (K2-EDTA, sodium citrate and lithium heparin). The concordance observed was 100% for all matrices, for both positive and negative specimen. The results are shown in the following table:

Independent Evaluation 1

(data and full report available upon request)

An evaluation was undertaken at an independent private laboratory to assess the performance of the kit, and to determine the suitability for routine use in the laboratory.

  1. Intra-assay precision, one known SARS-Cov-2 PCR positive sample was run 8 times in one day.
  2. Inter-assay precision, one known SARS-CoV-2 PCR positive sample was run 3 times over 5 days.
  3. Qualitative accuracy, a method comparison study was undertaken comparing the OnSite® test with an ELISA test using SARS-CoV-2 positive patients.
  4. Line intensity and clarity, dependent on antibody concentration, 2 serial dilutions performed with a known positive sample and 2 different diluents separately – a known negative sample, and 0 calibrator for immunoglobulins with a known concentration of 0 g/L for IgG and IgM.
  5. Analytical specificity of the assay, 134 negative samples obtained. Samples were collected prior to 2019. In addition, 20 PCR SARS-CoV-2 negative but other corona virus or common influenza virus PCR positive samples obtained for testing for potential cross-reactivity.
  6. Clinical sensitivity, 19 SARS-CoV-2 PCR positive serum samples obtained from patients after a time frame of >14 from initial PCR test.

All samples used in the study collected in plain blood collection tubes or gel barrier collection tubes and centrifuged to obtain the serum. All samples stored at 2-8°C short term or -20°C long term.

Results

Intra-assay and inter-assay data was concordant.

Qualitative accuracy study (OnSite® compared to ELISA) in patients with COVID-19 disease (23 pairs were available) gave 87% and 78% concordance for IgG and IgM, respectively in a head-to comparison, with overall concordance 100%.

The result from the dilution studies showed that the development of the line in the reader window is independent of sample concentration. Using either negative sample or 0 calibrator as diluents gave similar intensity and clarity of line throughout the different relative concentration ranges.

Of the 20 potentially cross-reactive samples, all gave negative results for COVID-19 IgG and IgM. Of the 134 negative screening samples, all gave negative results for IgG and IgM.

Clinical Performance Data

Of the 19 convalescent samples tested, 18 were IgG positive, 19 IgM positive and 19 IgG or IgM positive. The results are concordant with an ELISA assay except one IgG result which was found to be negative. The overall specificity is 100% with a sensitivity of 100%. The clinical performance in this group is shown in the table below:

Independent Evaluation 2

An evaluation was undertaken in the UK at a large Acute NHS Trust laboratory to assess the performance of the kit in comparison with the Abbott SARS-CoV-2 IgG test which is in routine use on the Architect system.

100 samples were selected, 70 negative 30 positive by the Abbott SARS-CoV-2 IgG test, and randomised before being blind tested with the OnSite® COVID-19 IgG/IgM Rapid Test.

All samples used in the study were collected in plain blood collection tubes and centrifuged to obtain the serum. All samples stored at 2-8°C short term or -20°C long term.

Results

Of the 70 confirmed negative samples tested, all 70 were negative by the OnSite® COVID-19 IgG/IgM Rapid Test.

Of the 30 confirmed positive samples tested, 29 were positive by both IgM and IgG, one sample was positive only with IgM.

Performance Data

OnSite® COVID-19 IgG test result compared to Abbott SARS-CoV-2 IgG result:

Sensitivity =                                        96.67%

Specificity =                                        100%

Negative Predictive Value =        98.59%

Positive Predictive Value =          100%

Discussion

All negative samples were confirmed negative by the OnSite® COVID-19 IgG/IgM Rapid Test indicating good specificity.

One positive sample (#67) was reported by the OnSite® COVID-19 IgG/IgM Rapid Test as negative for IgG but positive for IgM. While the overall result was reported as positive correlating with the confirmed serological status of the patient, further investigation into the sample showed the Abbott SARS-CoV-2 IgG result was 2.24. The interpretive guidance is to report ≤ 1.4 as non- reactive and ≥ 1.4 as reactive. There is no grey zone used in the laboratory as the results are reported with a disclaimer regarding conferred immune status of the patient. It is likely this patient is progressing from the primary stage of infection, wherein IgM levels are still detectable by the OnSite® COVID-19 IgG/IgM Rapid Test, but IgG levels are not yet at a high enough titration to be detected.

Overall, this small study showed good performance of the OnSite® COVID-19 IgG/IgM Rapid Test compared with the Abbott SARS-CoV-2 IgG Test, with the rapid test proving easy to use and showing clear results that were simple to interpret. The fast turnaround time and ease of use makes this an interesting possible addition to the current portfolio of testing methods used in the laboratory response to the SARS-CoV-2 pandemic.

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