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Covid-19 IgG

COVID Biomarker

Sample Needed

Collection Type: Blood

Body System

Related System: COVID

Overview

COVID-19 IgG is an antibody test that detects immunoglobulin G directed against SARS-CoV-2 (the virus that causes COVID-19). It measures whether a person has developed a longer‑term adaptive immune response from prior infection or vaccination (usually appearing 1–3 weeks after exposure). The test is used to document past infection, assess seroconversion after vaccination, or help evaluate unexplained symptoms consistent with prior COVID-19. Indications include prior respiratory illness, known exposure, or monitoring immune response in high‑risk or immunocompromised people. Results vary with time since infection/vaccination (levels peak then decline), age (older adults may mount lower responses), immunosuppression, and certain chronic conditions; gender differences are small.

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Test Preparation

No special preparation is required

Why Do I Need This Test

Profile: COVID - Symptoms/indications: recent or past COVID‑like illness, known exposure, or to check vaccine response - Diagnoses/monitoring: documents past infection or seroconversion after vaccination; helps in epidemiologic or occupational screening - Reasons for abnormal results: recent infection (positive), no prior exposure or poor immune response (negative), waning antibodies over months - Biological meaning: positive = detectable IgG consistent with prior immune exposure; negative = no detectable IgG or very early/very late testing - Behaviors/factors: immunosuppressive drugs, certain chronic illnesses, age, smoking, obesity can reduce antibody production - Family history: known primary immunodeficiency may prompt testing

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Understanding Test Results

A "negative" result (below the assay cutoff e.g., Euroimmun <0.8 ratio, Abbott <1.4 index, Roche <1.0 COI) means no detectable IgG and suggests no prior infection or vaccine response, or testing too early/late.
A "borderline"/equivocal range (e.g., Euroimmun 0.8–1.1) requires repeat testing in 1–2 weeks.
A "positive" result (above the assay cutoff: e.g., Euroimmun >1.1, Abbott ≥1.4, Roche ≥1.0) indicates prior infection or vaccination and likely some degree of immunity; higher quantitative values generally correlate with stronger humoral response but do not guarantee sterilizing immunity.
Very high antibody levels soon after vaccination/infection indicate recent strong response; declining levels over months are expected and do not by themselves define susceptibility.
Absence of IgG in immunocompromised patients may signal poor vaccine protection and need for additional evaluation or repeat vaccination.
Always interpret with clinical context, timing since exposure/vaccination, and the specific assay’s reference ranges.

Normal Range

Common assay-dependent negative cutoffs (examples): Euroimmun IgG ratio <0.8 (ratio); Abbott Architect IgG index <1.4 (index); Roche anti‑S COI <1.0 (COI). Quantitative assays report AU/mL or BAU/mL with lab-specific cutoffs (refer to your laboratory report).

FAQs

Q: What does COVID-19 IgG positive mean?

A: COVID-19 IgG positive means your blood contains IgG antibodies to SARS-CoV-2, indicating prior infection or a response to vaccination. It suggests some immune memory but does not guarantee complete or long-term protection. IgG usually appears weeks after exposure and can wane over months. Test timing and accuracy matter; discuss what the result means for vaccination and precautions with your healthcare provider.

Q: Does COVID affect IgG?

A: COVID-19 stimulates production of SARS‑CoV‑2‑specific IgG antibodies, typically appearing 1–3 weeks after exposure and peaking weeks later. Levels decline over months but memory B cells often persist, providing longer-term protection. Severe infection or vaccination usually yields higher IgG titers, while older or immunocompromised people may mount weaker responses. Total IgG generally remains normal, but specific anti‑SARS‑CoV‑2 IgG fluctuates.

Q: What does IgG test positive mean?

A: A positive IgG test means your immune system has produced IgG antibodies to a specific pathogen, indicating past infection or vaccination and prior exposure. It usually appears days to weeks after infection and suggests some immune memory, but does not prove current active infection or guaranteed protection. Interpretation depends on timing, symptoms, and other tests; discuss results with your healthcare provider.

Q: What is the IgG IgM test for COVID-19?

A: The IgG/IgM test is a blood antibody test that detects immune responses to SARS-CoV-2: IgM usually appears early after infection, indicating recent exposure, while IgG appears later and suggests prior infection or developing immunity. It helps assess past infection and population exposure but isn’t the primary test for acute diagnosis (PCR/antigen are used). Timing affects accuracy, and false results can occur.

Q: How to read IgG results?

A: IgG results are usually reported as negative, equivocal/indeterminate, or positive, often with a quantitative value and lab-specific reference range. A positive IgG suggests past infection or vaccination and possible immunity; a negative result indicates no detectable prior response or waning antibodies. Timing, test sensitivity, and cross-reactivity affect interpretation. Discuss results with your healthcare provider for clinical context and next steps.

Q: How long do COVID IgG antibodies last?

A: COVID-19 IgG antibodies typically peak a few weeks after infection or vaccination, then decline over months. Most people still have detectable IgG for about 6–12 months, though levels fall and vary individually. Memory B and T cell responses often persist longer, helping protect against severe disease even when antibodies wane. Reinfection remains possible, especially with new variants.