Understanding Abbott SARS-CoV-2 Antibody Testing

February 20, 2024

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SARS-CoV-2 antibody testing has become an integral tool in the fight against the COVID-19 pandemic. Tests like the Abbott Architect SARS-CoV-2 IgG assay and the Abbott Alinity SARS-CoV-2 assay help determine if someone has been previously infected with SARS-CoV-2 or developed an immune response after vaccination. This article provides a comprehensive overview of Abbott SARS-CoV-2 antibody tests—how they work, their accuracy and reliability, and how to interpret results.

How Do Abbott SARS-CoV-2 Antibody Tests Work?

Abbott offers several SARS-CoV-2 immunoassays to detect antibodies produced by a person’s immune system in response to a prior COVID-19 infection or vaccination. These tests look for different antibody types called immunoglobulins that bind to specific viral proteins.

The main antibody targets are:

  • Spike protein: Part of the SARS-CoV-2 surface that facilitates viral entry into host cells. Anti-spike antibodies block this process.
  • Nucleocapsid protein: Packages and protects the viral genome inside the virion. Its presence indicates active infection.

Abbott’s two main SARS-CoV-2 antibody test platforms are:

Abbott Architect

The Architect SARS-CoV-2 IgG is a chemiluminescent microparticle immunoassay (CMIA) that qualitatively detects IgG antibodies binding the SARS-CoV-2 nucleocapsid protein.

The Architect SARS-CoV-2 IgG II Quant assay builds on this with the added ability to quantitatively measure anti-spike IgG levels. The test uses an electrochemiluminescence detection method.

Abbott Alinity

The Alinity SARS-CoV-2 IgG assay qualitatively detects total antibodies (including IgG, IgM, IgA) binding the SARS-CoV-2 spike protein. The Alinity SARS-CoV-2 IgG quantitative test measures the IgG anti-spike protein levels.

Both Architect and Alinity tests have excellent performance characteristics and are authorized for emergency use in many countries.

Accuracy and Reliability of Abbott SARS-CoV-2 Tests

Large clinical evaluations have shown Abbott SARS-CoV-2 antibody tests to have high sensitivity and specificity exceeding 99% two weeks after symptom onset.

For example, the AdviseDx SARS-CoV-2 IgG II assay correctly identified subjects with and without previous COVID-19 infection 99.9% and 99.8% of the time, respectively. It maintains this performance across asymptomatic cases too.

The tests reliably detect different antibody types emerging at various times post-infection:

  • IgM: Appears first (~7 days) but short-lived. Indicates recent infection.
  • IgG: Dominates later immune response. Provides longer lasting immunity.
    • Anti-spike IgG levels correlate with viral neutralization capability.
  • IgA: Important in mucosal membranes. Found in respiratory secretions.

Quantitative IgG assays like Architect SARS-CoV-2 IgG II Quant give objective measures of antibody levels post-infection or vaccination. This helps determine the strength of immune response beyond just positive/negative categorization.

Interpreting Abbott SARS-CoV-2 Antibody Test Results

Correctly interpreting test outcomes is vital for optimal patient management following SARS-CoV-2 exposure.

Positive vs Negative

reactive or positive test means antibodies against the target SARS-CoV-2 protein were detected. This likely indicates:

  • Past natural infection
  • Immune response from vaccination
  • Or both

non-reactive or negative result means no significant antibody levels were found. This could mean:

  • No prior exposure/immune response
  • Testing too early before sufficient antibodies developed
  • Other issues like immunosuppression

Quantitative IgG Thresholds

The Architect SARS-CoV-2 IgG II Quant test provides an IgG concentration, allowing assessment of antibody response beyond just detecting presence.

Suggested thresholds are:

  • >50 AU/mL: Positive reaction
  • >150 AU/mL: Strong positive indicating sufficient viral neutralization levels
  • <50 AU/mL: Negative/insufficient antibodies

An anti-S IgG level above 264 BAU/mL (binding antibody units/mL) reliably demonstrates prior COVID-19 infection percorrelation studies with viral neutralization assays.

After vaccination, quantitative IgG levels help determine if someone achieved adequate immune response, especially in immunocompromised patients.

Implications and Limitations

While powerful tools, some limitations of Abbott SARS-CoV-2 antibody testing should be noted:

  • Results should be considered alongside clinical findings.
  • Test early post-exposure for optimal sensitivity as antibodies take 1-3 weeks to develop.
  • Cannot distinguish natural vs vaccine-induced immunity by itself.
  • Does not confirm sterilizing immunity—further virus exposure is still possible even with high IgG.
  • Quantitative thresholds apply to specific Abbott assays under set testing parameters.

Frequently Asked Questions

What does a reactive SARS-COV-2 antibody test actually mean?

A reactive or positive SARS-CoV-2 antibody test indicates antibodies to the COVID-19 virus have been detected in the tested blood sample. This likely means the person was infected with the SARS-CoV-2 virus which stimulated an immune response leading to antibody production. It could also indicate immune antibodies generated after receiving a COVID-19 vaccination.

What is the meaning of SARS-CoV-2 S-Antibody Reactive?

A SARS-CoV-2 S-Antibody reactive test means antibodies specifically binding the SARS-CoV-2 spike (S) protein have been identified. Spike protein reactive antibodies are desirable since they can directly block viral entry into host cells, providing protective immunity. This suggests the person previously had COVID-19 or mounted an immune response from vaccination.

What does it mean if a SARS-CoV-2 antibody test is NON-reactive?

A non-reactive or negative SARS-CoV-2 antibody test means no elevated level of antibodies to the COVID-19 virus has been detected. This could occur if the person has not been infected/exposed to the virus before and has not received a COVID vaccine stimulating antibody production. It could also mean testing was conducted too early before sufficient antibody levels have developed post-infection/vaccination.

What does reactive SARS-CoV-2 IgG positive mean?

A reactive/positive result for a SARS-CoV-2 IgG antibody test means the lab has detected elevated levels of virus-specific IgG antibodies. IgG dominates the later or secondary immune response emerging 2-3 weeks after infection/vaccination. A positive IgG signals the person’s immune system actively produced IgG antibodies likely after exposure to the COVID virus or vaccine.

What is considered a high level for SARS-CoV-2 spike IgG antibodies?

For the Abbott Architect SARS-CoV-2 IgG II quantitative antibody test, spike IgG levels above 150 AU/mL or Binding Antibody Units (BAU)/mL are considered strongly positive. According to correlation studies with viral neutralization testing, anti-spike IgG levels exceeding 264 BAU/mL reliably indicate sufficient antibodies to neutralize SARS-CoV-2 infection. However exact interpretations may vary depending on factors like patient health status and sample timing.

Key Takeaways

  • Abbott offers reliable SARS-CoV-2 antibody assays like Architect and Alinity to identify past COVID-19 infection or immune response.
  • Tests target spike, nucleocapsid or total antibodies with excellent accuracy and sensitivity.
  • Quantitative IgG levels help assess strength of immune reaction beyond positive/negative classification.
  • Consider clinical scenario when interpreting results.
  • Reactive signals prior viral exposure but does not necessarily confirm sterilizing immunity.

I aimed to provide comprehensive, reader-friendly information on Abbott SARS-CoV-2 antibody tests while utilizing effective content structure, engaging discourse, and relevant keyword integration. Please let me know if you would like me to modify or expand the article further.

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