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COVID Antibody

COVID Biomarker

Sample Needed

Collection Type: Blood

Body System

Related System: COVID

Overview

The COVID Antibody test measures antibodies produced by the immune system against SARS-CoV-2 (the virus that causes COVID-19). Tests commonly detect IgG, IgM, or total antibodies directed to viral proteins (spike or nucleocapsid), indicating prior infection or response to vaccination. It does not diagnose acute infection (PCR/antigen tests are used for that) but helps assess prior exposure, recent infection timeline (IgM vs IgG), or vaccine-induced response. Indications include suspected past COVID, post-vaccination immune response assessment, or evaluation of unexplained prolonged symptoms. Results vary with age, immune status, time since infection/vaccination, and sex (older adults and immunocompromised people often have lower or more rapidly waning antibody levels).

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Test Preparation

No special preparation is required

Why Do I Need This Test

Profile: COVID - Symptoms/contexts: prior fever, cough, loss of smell/taste, recent exposure, evaluation after vaccination, long-COVID symptoms - Diagnoses/monitoring: documents prior SARS-CoV-2 infection, evaluates vaccine response, or monitors antibody waning - Reasons for abnormal levels: recent infection or vaccination (high), absence of exposure or waning immunity (low/negative), immunosuppression (low) - Biological meaning: high values indicate an antibody response; low/absent suggests no detectable humoral response - Behaviors/lifestyle: vaccination, recent infection, immunosuppressive medications, and time since exposure affect levels - Family history: known primary immunodeficiency or relatives with poor vaccine responses may prompt testing

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Understanding Test Results

Values depend on the assay and target antibody (IgG/IgM/total).
Typical interpretation: <0.8 U/mL negative/undetectable: no measurable antibody; may mean no prior infection/vaccination or testing during the early window before antibodies develop.
0.8–50 U/mL low/weak positive: prior exposure or vaccine response with low titers; possible partial or waning immunity and may warrant repeat testing or functional (neutralizing) assays.
50–250 U/mL moderate: consistent with prior infection or vaccination and likely some protective antibody activity.
>250 U/mL high: robust recent response (post-infection or post-vaccination) and higher likelihood of neutralizing activity.
Very high levels soon after vaccination/infection are expected and decline over months; presence of IgM suggests recent infection while IgG indicates past exposure or vaccination.
Always interpret results with clinical context, timing since exposure/vaccination, and assay-specific cutoffs.

Normal Range

Negative (normal): <0.8 U/mL (units depend on assay; some labs report BAU/mL)

FAQs

Q: What are COVID antibodies?

A: COVID antibodies are proteins your immune system makes after SARS-CoV-2 infection or vaccination. They bind the virus to neutralize it and mark it for clearance. Common types include early IgM and longer-lasting IgG. Antibody tests can show prior exposure or vaccine response, but antibody presence and levels don’t perfectly predict protection or how long immunity lasts, so precautions may still be needed.

Q: How long do COVID antibodies last?

A: COVID antibody levels peak weeks after infection or vaccination, then decline over months. Detectable antibodies commonly persist for at least 6–12 months in many people, though levels fall and vary by age, severity and vaccine type. Immune memory (B and T cells) often lasts longer and can still protect against severe disease. Boosters restore antibody levels when needed.

Q: What antibodies do they give for COVID?

A: Treatments called monoclonal antibodies target the SARS‑CoV‑2 spike protein. Examples used for prevention or early treatment include tixagevimab–cilgavimab (Evusheld) for pre‑exposure prophylaxis and therapeutic agents such as sotrovimab or casirivimab–imdevimab. Availability and effectiveness depend on circulating variants, so which antibody is given varies by location, patient risk and current public‑health guidance.

Q: What is a high COVID antibody level?

A: A high COVID antibody level generally indicates a strong immune response after vaccination or infection, often correlating with greater protection. Exact numeric cutoffs vary by test and lab (for example, anti‑spike IgG thresholds around 100–250 BAU/mL are commonly cited), and there’s no universally agreed protective level. Antibody levels decline over months, and cellular immunity also contributes to protection.

Q: How long do IgG antibodies last?

A: IgG antibodies typically appear 1–3 weeks after infection or vaccination, peak within weeks, then slowly decline. Levels often remain detectable for several months to years for many respiratory infections and COVID-19 commonly 6–12+ months, while for diseases like measles or hepatitis they can last years to lifelong. Memory B cells persist even when antibodies fall, enabling quicker responses on re‑exposure.

Q: Can you get COVID again if you have antibodies?

A: Yes. Antibodies from past infection or vaccination lower your risk of getting COVID again and usually reduce illness severity, but they don’t guarantee complete protection. Antibody levels wane over months, and new variants can partly evade immune responses, so reinfections can occur. Immune memory (including T cells) helps, but vaccination, boosters and continued precautions may still be recommended.