What this test measures
ELISA (Enzyme-Linked Immunosorbent Assay) is a plate-based laboratory test that detects IgG antibody against SARS-CoV-2 in serum or plasma. The result is reported as reactive/non-reactive or as an index value.
The assay is widely used in Indian labs and was the workhorse of early Indian COVID-19 serosurveys. ICMR-developed COVID-Kavach ELISA was deployed across the country in 2020–21 for national seroprevalence mapping.
Why it matters
COVID IgG ELISA is used to confirm past SARS-CoV-2 exposure or vaccine response, in seroprevalence research (multiple ICMR national serosurveys), in clinical settings to support a past COVID-19 diagnosis where RT-PCR was never done, and occasionally for immunocompromised patient assessment.
For healthy adults, routine antibody testing is not recommended by WHO, CDC, or ICMR for clinical decisions. CLIA has largely replaced ELISA in private Indian labs because of faster turnaround and higher throughput, but ELISA remains the standard in many government and research labs.
How to prepare
No fasting required. The test can be done at any time of day. Mention vaccination history and any prior COVID-19 diagnosis.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Anti-SARS-CoV-2 IgG (ELISA) (OD ratio / Index / Reactive-Non-reactive)[1][2] | Reactive in vaccinated or recovered individuals | Non-reactive — no detectable IgG by ELISA. Possible reasons: never exposed, antibody waned, immunocompromised non-responder, or tested too early after vaccination. | Reactive — IgG present, indicating past infection, vaccination, or both. Does not measure functional protection; absolute correlation with immunity is not established. |
When to use COVID IgG ELISA
| Scenario | Best test | Why |
|---|---|---|
| Past infection confirmation | IgG ELISA or CLIA | Both work |
| Vaccine response assessment | Quantitative IgG (BAU/mL) | Numeric titre is more useful |
| Serosurvey | ELISA | High-throughput, cost-effective |
| Diagnose current COVID-19 | RT-PCR / Rapid Antigen | Antibody is for past infection |
| Immunocompromised follow-up | Quantitative IgG + neutralisation | Functional assessment needed |
Frequently asked questions
Is ELISA the same as CLIA for COVID antibody?
Both detect IgG antibody. CLIA is generally faster and has slightly higher sensitivity; ELISA is high-throughput and cost-effective. Clinical interpretation is the same.
How soon after vaccination should I test by ELISA?
At least 2–4 weeks after the dose for stable antibody response.
Can ELISA distinguish vaccine from infection antibody?
Most spike-based ELISAs cannot. ICMR-developed nucleocapsid-based ELISAs (like Covid-Kavach) can detect infection-induced antibody specifically.
My ELISA is reactive but I never had symptoms. How?
Asymptomatic COVID-19 is common — most adults in India have had at least one subclinical infection. Vaccination alone also produces reactive ELISA.
Is ELISA used for diagnosing current COVID-19?
No — antibody develops 2–4 weeks after infection. Current infection is diagnosed by RT-PCR or rapid antigen.
Does a positive ELISA mean lifelong immunity?
No. SARS-CoV-2 immunity wanes over months and variants can evade antibody response. Continued vaccination per public health guidance is important.
Is the test useful in children?
Routine testing is not recommended. Used selectively in research and immunocompromised children.
Related Infectious Disease tests
Tests commonly ordered alongside COVID ANTIBODY IGG - ELISA, or that help interpret an unexpected result.
Sources & references
- CDC — COVID-19 Antibody Testing · accessed 2026-05-30T00:00:00.000Z
- WHO — COVID-19 Antibody Testing Guidance · accessed 2026-05-30T00:00:00.000Z
- ICMR India — COVID-19 Guidance and COVID-Kavach · accessed 2026-05-30T00:00:00.000Z
- NIV Pune — COVID-19 Serology · accessed 2026-05-30T00:00:00.000Z
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