8 Tests for detecting Covid-19 that you might not know.

To diagnose Coronavirus (COVID-19) infection has become very important.  The importance of reliability, the increasing need for screening have grown importance these days. These test

There are tests to diagnose the current infection (antigen test) and past infection (antibodies test). In both scenarios, different types of samples need to be taken. 

What are different tests to Diagnose Covid-19? 

  1. Current infection:
    1. Polymerase chain reaction (PCR)
      1. Open System:
        • RTPCR machine (ABI 7500, Rotor gene Q, Roche light cycler, Biorad CFX-96, Qiagen)
      2. Closed system:
        • Truenat ( Molbio Diagnostics)
        • CBNAAT/ Gene Xpert (Cepheid company)
        • Bioarray – Multiplexing (Biofire)
    2. Rapid antigen test/ Lateral flow assay/ point care testing
  2. Past infection:
    1. Rapid Antibody kit
    2. Laboratory-based immunoassays
      • Covid Antibody IgG
      • Total Covid Antibody IgM +IgG

Now let’s start a brief introduction about each test one by one, which you need to know and also how to read the result.

Polymerase chain reaction (PCR)

Polymerase chain reaction is considered as confirmatory for diagnosis of Covid infection.

Rapid antigen test gives results with 15 minutes. It yields confirmed positives but doesn’t exclude false negatives.

Antibody test (or serology) helps to diagnose antibodies formed after infection or vaccination. It doesn’t help in the diagnosis of active infection.

PCR test used to diagnose the presence of viral RNA. The best time to do a PCR test 5th to 7th day of the infection. PCR test detects viral RNA in the body before antibodies have formed. Therefore, it detects that someone has an early infection period or not.

The best specimen for PCR is a nasopharyngeal swab or Bronchoalveolar Lavage (BAL). Other specimens that can be used are oropharyngeal swab, saliva but has lesser accuracy.

Rapid Antigen Test or Lateral Flow Test:

Rapid antigen kits are a easy and quick diagnostic tool. It is designed to give active Covid-19 infection, not antibodies to the disease.

Best sample: Nasopharyngeal swab sample.

The sample is placed on the absorbent pad of the lateral flow assay. Then, it flows along with the pad via a capillary line to the strip coated with antibodies.

If the sample contains specific SARS Cov-2 proteins, it will bind to the antibodies and show as the colored line on the test, indicating infection.

Antibodies test

If you are looking whether you had developed antibodies after Covid-19 infection. The best time to do an antibody test is after 2-3 weeks of infection.

This test also tells whether antibodies have developed after vaccination or not. The best time for test after vaccination is 2- 3 weeks later of 2nd dose of vaccination.

For this test, the sample should be taken is venous blood.

Who should get tested for COVID-19 infection?

  1. If you have symptoms of Covid-19
  2. If you are a contact
  3. If you are asked or referred to get tested by your doctor or health care provider.
  4. If you are potentially exposed to the virus
  5. If you have tested positive for COVID-19 in recent 3 months and recovered well. There is no need for repeat testing if they don’t develop new symptoms.
  6. If you have taken part in some activities which involve high-risk group areas for COVID-19, where you couldn’t follow physical distancing such as travel, attending a mass gathering, being in a crowd, being in an enclosed space or poorly ventilated area for a long time.

It’s important to know that whether you are vaccinated or not, if you are having any symptoms, you should get yourself tested. Even CDC also recommends this.

How to test for COVID-19 infection?

You should contact your local health care provider.

If possible, some may come to your home to collect sample, if you have any signs and symptoms of COVID-19.

How to understand results of COVID-19 tests?

If your test is Positive or Negative, the first thing to check is what test is done for you and follow the instructions below:

How to read your RTPCR report:

If your test comes positive, it's a confirmed positive.

No need for extra testing. Unnecessary testing will waste your time and may delay your treatment. When your test comes positive, first and foremost you need to consult your doctor. You can explain your symptoms to your doctor. Your doctor will establish whether you will get treated in-home or you need hospitalization.

If your test comes Negative, it's a confirmed Negative. 

If you have symptoms and the test comes as Negative, it means that your report is False Negative. The false-negative result may depend on the various factors. Mainly it may occur if the sample is not taken correctly or have transported to the testing lab not properly. 

Inaccurate results may also occur when you have given your sample very early or very late of the infection. The best time for testing for current infection is the 5th- 7th day

If your test is Inconclusive, then reapeat test after 2-3 days.

An inconclusive result means your screening test has come positive and your confirmatory test has come negative. The probable reason for this is more Ct value (above 33). This means the detectable DNA is less in the sample.

How to read Rapid Antigen test report:

If your rapid antigen test comes positive, it's a confirmed positive.

You can tell your symptoms to your doctor and start the treatment.

If your rapid antigen test is Negative, it is not a confirmed that you are Covid negative.

There will be a doubt that you might have the infection. RAT test doesn’t confirm True Negative, unlike True positive results. A negative RAT test and you are having any symptoms, you need to do an RTPCR test to confirm COVID-19 infection. RAT test is better when you are in a hurry and you need a report on an ASAP basis.

How to read Covid Antibodies test report:

Different antibody tests have different biological reference interval values. Please correlate your results with the parameters given by your lab and consult your doctor.