What this test measures
CLIA (Chemiluminescence Immunoassay) is a highly sensitive lab platform that detects IgG antibody against SARS-CoV-2 in serum or plasma. The result is qualitative (reactive/non-reactive) or semi-quantitative depending on the assay.
Most CLIA assays target the spike protein or its receptor-binding domain — the same target as Covishield and most other COVID-19 vaccines. Nucleocapsid-targeted CLIA assays (less common in India) detect infection-induced antibody specifically.
Why it matters
CLIA is the preferred lab platform for COVID-19 IgG in most NABL-accredited Indian labs because of its high sensitivity (>95%) and specificity (>98%) compared to rapid card tests or older ELISA versions. It is used for clinical confirmation of past infection or vaccine response, for ICMR-led serosurveys, in immunocompromised patient assessment, and for occasional pre-employment or pre-procedural requirements.
For healthy adults, routine antibody testing is not recommended by WHO, CDC, or ICMR for clinical decisions. The test is more useful in immunocompromised patients where vaccine response may be poor and additional doses or passive immunisation are considered.
How to prepare
No fasting required. The test can be done at any time of day. Mention vaccination history and 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 (CLIA) (Index / Reactive-Non-reactive)[1][2] | Reactive in vaccinated or recovered individuals | Non-reactive — no detectable IgG. Either never exposed, never vaccinated, antibody waned, or immunocompromised non-responder. Quantitative testing can help characterise the response. | Reactive — IgG present from past infection, vaccination, or both. Indicates likely past exposure/immunity; absolute protection against re-infection is not guaranteed. |
COVID IgG platform comparison
| Platform | Sensitivity | Specificity | Turnaround | Best use |
|---|---|---|---|---|
| CLIA | ~95–98% | ~98–99% | Hours | Clinical and research use |
| ELISA | ~92–95% | ~95–98% | 4–8 hours | High-throughput labs |
| Rapid card | ~85–95% | ~92–98% | 15 minutes | Point-of-care triage |
| Neutralisation assay | High | High | Days | Research; functional immunity |
Frequently asked questions
Is CLIA more accurate than rapid antibody tests?
Yes. CLIA has higher sensitivity and specificity than rapid card tests. For confirming past infection or vaccine response in clinical or research settings, CLIA is preferred.
Can CLIA tell me if my antibodies are from vaccination or infection?
Most CLIA assays target spike protein and cannot distinguish. Nucleocapsid-targeted CLIA assays (less common in India) can identify infection-induced antibody.
How soon after a COVID vaccine dose should I test IgG?
At least 2–4 weeks after the dose to allow antibody to develop. Earlier testing can give a false negative.
I am vaccinated but my CLIA IgG is negative. Why?
Possible reasons: antibody has waned, immunocompromised state, assay variability, or rarely vaccine non-response. Discuss with your doctor — additional doses may be appropriate for immunocompromised patients.
Do I need this test before travel?
Most countries no longer require COVID antibody testing for entry. Check current travel advisories before booking.
Is the test useful in pregnancy?
It can confirm past exposure or vaccine response. Routine antibody testing is not part of antenatal care.
Can a positive IgG mean I have current COVID-19?
No. IgG develops 2–4 weeks after infection or vaccination. Current infection is diagnosed by RT-PCR or rapid antigen.
Related Infectious Disease tests
Tests commonly ordered alongside COVID ANTIBODY IGG - C.L.I.A, 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 · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — COVID-19 Antibody Test · accessed 2026-05-30T00:00:00.000Z
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