How do the rapid IgM-IgG antibody tests for SARS-CoV-2 work?

Alberto Martín

Lucare Ibérica answer your questions about the Rapid IgM-IgG Antibody Test for SARS-CoV-2

How do the Rapid IgM-IgG Antibody Tests for SARS-CoV-2 work?

Unlike the PCR technique used for the diagnosis of COVID-19 which takes several hours, the rapid tests are able to give a result within 15 minutes. Also
called serological tests where a blood sample is taken to detect the antibodies produced by the body's defences days after being infected by the virus.

The kits work similarly to pregnancy tests and are based on a technique called paper-based immunochromatography. It consists of a paper that has either
antibodies that recognise the proteins of the virus, in the case of antigens, or virus molecules that recognise the antibodies generated by our body to defend itself, in the case of serologies. a coloured line appears on the device when the patient is positive for SARS-CoV-2.

The antibody tests do not detect the virus directly, but rather the antibodies that the body has produced to defend itself against it. The result also indicates that the person
is or has been infected, but is reached by a different route. In particular, two types of antibody are recognised:

  • Immunoglobulin M (IgM): These are the first to appear in any infection. They occur approximately 5-7 days later than the appearance of symptoms. 
  • Immunoglobulin G (IgG): These can take time to form after defeating an infection or after administration of a vaccine, but are usually detectable in
    blood from 15-20 days.

Clungene COVID-19 IgG - IgM Rapid Test:

The Clongene Biotech rapid test has a very high sensitivity and specificity for both IgM (96.8% / 100%) and IgG (93.1% / 96.7%).

Performance of the Rapid Antibody Test (IgM - IgG):

  1. Remove the test cassette from the sealed bag.
  2. Hold the dropper vertically and transfer 1 drop (approximately 10μl) of
    the sample at the front of the sample well (S) making sure there are no bubbles
    of air. For greater accuracy, transfer the sample using a pipette capable of
    deliver 10μl volume.
  3. Then add 2 drops (approx. 70μl) of tampon immediately
    in the sample well (S).
  4. Start the timer.
  5. Wait for the coloured lines to appear. 6.Interpret the test results to
    the 15 minutes. Do not read the results after 20 minutes.

Interpretation of results

  • IgM negative and IgG negative: No antibodies have been generated, apparently not
    the disease. However, a negative result for both antibodies does not rule out 100% of the
    infection. It could be that your immune system has not yet generated antibodies by
    be in an early stage (less than 7 days) of infection. Be vigilant.
  • IgM positive and IgG negative: early stage of infection. Contagiousness. If it has not been done, it
    recommends a PCR test.
  • Positive IgM and positive IgG: disease in advanced or past evolution It could be contagious,
    although the probability is low. If this has not been done, a PCR test is recommended.
  • IgM negative and IgG positive: past infection and cured. It has generated antibodies. It is not contagious.

Internal use document for Lucare Ibérica and distributors. Lucare Ibérica is not responsible for the misinterpretation of the information detailed in this document