COVID-19 Testing


Two kinds of tests are available for COVID-19: viral tests and antibody tests.

  • A viral test tells you if you have a current infection.
  • An antibody test might tell you if you had a past infection.

A) Test for Current Infection (Viral Test)

1) Rapid Antigen Detection Test for COVID-19

There is urgent need of a reliable point-of-care rapid antigen detection test with good sensitivity and specificity for early detection of the disease.

  • It reduces the burden of relying on just RT-PCR tests to identify COVID-19 patients.
    "Antigen testing is useful because even if it’s less sensitive, it is rapid and the results that are positive will be positive "So, patients who test positive can get into isolation faster."
  • Antigen tests remove about half of the positives from the testing load.
  • Antigen tests are also inexpensive compared to RT-PCR.
  • An antigen test can only reveal whether a person is currently infected with SARSCoV2. Before or after the infection has passed, antigens won't be present.
  • Since antigen testing doesn't involve any processes of amplifying the virus or its genetic material, a swab sample may have too little antigen to be detected. This could produce a false negative result. As a precaution, a negative test should be followed up by the more accurate RT-PCR test, to confirm a true negative for COVID-19.
  • Accuracy is the single largest problem with antigen tests, which are much less sensitive than RT-PCR as a diagnostic tool.
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Real Time RT-PCR is the Gold standard test for detecting cases of COVID-19. The advantage of this platform lies in its accuracy of detection.However, wherever available, it is advised to use real time RT-PCR as the front line test for diagnosis of SARS-CoV-2.

An RT-PCR test is considered very reliable because it can detect even a single virus particle in swabs taken from inside the mouth or nose, where the virus particles are most prevalent.

Advantages of RT-PCR testing
  • Sensitive and specific: There are real-time variations of the RT–PCR technique that are quick, super sensitive, and specific. They can deliver a reliable diagnosis in three hours. That said, the process on average takes around eight hours to produce a conclusive result.
  • More accurate, less prone to contamination: Compared to other methods to isolate and detect viruses, RT–PCR is much faster and less likely to be contaminated or cause errors during the testing process.
  • Severity of infection can be estimated: A standard real-time RT–PCR set-up usually goes through 35 cycles, which means that, by the end of the process, around 35 billion new copies of the sections of viral DNA are created from each strand of the virus present in the sample.
Limitations of RT-PCR Testing

Only detects ongoing infection: The main limitation of RT-PCR testing is that it cannot be used to detect a past infection with SARS-CoV-2, which is important for understanding the development and spread of the virus, as viruses are only present in the body for a specific window of time.

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3) The TrueNat and CBNAAT systems

  • These have also been deployed for diagnosis of COVID-19 in view of availability of customized cartridges. These platforms have a quick turnaround time (30-60 minutes) but only 1-4 samples can be tested in one run, limiting the maximum numbers that can be tested to 24-48 samples / day only.
  • TrueNat is a chip-based, portable RT-PCR machine.The device is on its way to becoming one of the main diagnostic tools for COVID- 19 as India looks to expand its testing capacity. It is the fastest available PCR-based technique recommended by ICMR till date.
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B) Test for Past Infection (Antibody Test)

IgG Antibody test for COVID-19 (Only for surveillance and not diagnosis):

IgG antibodies generally start appearing after two weeks of onset of infection, once the individual has recovered after infection and last for several months. Therefore, the IgG test is not useful for detecting acute infection. However, detection of IgG antibodies for SARS-CoV-2 may be useful in the following situations:

  • a. Serosurveys to understand the proportion of population exposed to infection with SARS-CoV-2 including asymptomatic individuals. Depending upon the level of seroprevalence of infection, appropriate public health interventions can be planned and implemented for prevention and control of the disease. Periodic serosurveys are useful to guide the policy makers.
  • b. Survey in high risk or vulnerable populations (health care workers, frontline workers, immunocompromised individuals, individuals in containment zones etc) to know who has been infected in the past and has now recovered.
Antibody testing for COVID-19 may be done if:
  • You had symptoms of COVID-19 in the past but weren't tested.
  • You're about to have a medical procedure done in a hospital or clinic, especially if you've had a positive COVID-19 diagnostic test in the past.
  • You've had a COVID-19 infection in the past and want to donate plasma, a part of your blood that contains antibodies that can help treat others who have severe cases of COVID-19.

Results of COVID-19 antibody tests may not always be accurate, especially if the test was done too soon after infection or the test quality is questionable.

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Advisory on Strategy for COVID-19 Testing in India
(Version VI, dated 4th September 2020)

Recommended by the National Task Force on COVID-19 - ICMR

A. Routine surveillance in containment zones and screening at points of entry:

Choice of Test (in order of priority):

  • i. Rapid Antigen Test (RAT) [as per attached algorithm]
  • ii. RT-PCR or TrueNat or CBNAAT
  • 1. All symptomatic (ILI symptoms) cases including health care workers and frontline workers.
  • 2. All asymptomatic direct and high-risk contacts (in family and workplace, elderly ≥ 65 years of age, immunocompromised, those with co-morbidities etc.) of a laboratory confirmed case to be tested once between day 5 and day 10 of coming into contact.
  • 3. All asymptomatic high-risk individuals (elderly ≥ 65 years of age, those with co-morbidities etc.) in containment zones.

*RAT for containment zone: Ideally, it is suggested that 100% people living in containment zones should be tested by RAT particularly in cities where there has been widespread transmission of infection.

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B. Routine surveillance in non-containment areas:

Choice of Test (in order of priority):

  • i. RT-PCR or TrueNat or CBNAAT
  • ii. Rapid Antigen Test (RAT)*
  • 4. All symptomatic (ILI symptoms) individuals with history of international travel in the last 14 days.
  • 5. All symptomatic (ILI symptoms) contacts of a laboratory confirmed case.
  • 6. All symptomatic (ILI symptoms) health care workers / frontline workers involved in containment and mitigation activities.
  • 7. All symptomatic ILI cases among returnees and migrants within 7 days of illness.
  • 8. *All asymptomatic high-risk contacts(contacts in family and workplace, elderly ≥ 65 years of age, those with co-morbidities etc. [RAT is recommended as the first choice of test in order of priority]
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C. In Hospital Settings:

Choice of Test (in order of priority):

  • i. RT-PCR or TrueNat or CBNAAT
  • ii. Rapid Antigen Test (RAT)
  • 9. All patients of Severe Acute Respiratory Infection (SARI).
  • 10. All symptomatic (ILI symptoms) patients presenting in a healthcare setting.
  • 11. Asymptomatic high-risk patients who are hospitalized or seeking immediate hospitalization such as immunocompromised individuals, patients diagnosed with malignant disease, transplant patients, patients with chronic co-morbidities, elderly ≥ 65 years.
  • 12. Asymptomatic patients undergoing surgical/non-surgical invasive procedures (not to be tested more than once a week during hospital stay).
  • 13. All pregnant women in/near labor who are hospitalized for delivery.
Points to be noted:
  • No emergency procedure (including deliveries) should be delayed for lack of test. However, sample can be sent for testing if indicated as above (1-13), simultaneously.
  • Pregnant women should not be referred for a lack of testing facility. All arrangements should be made to collect and transfer samples to testing facilities.
  • Mothers who test positive for COVID-19 should be advised to wear a mask and undertake frequent handwashing while handling their baby for 14 days. They should also be advised on breast cleaning before feeding the neonate. These measures are likely to reduce transmission of COVID-19 to their babies.
  • 14. All symptomatic neonates presenting with acute respiratory / sepsis like illness. (Features suggestive of acute respiratory illness in a neonate are respiratory distress or apnea with or without cough, with or without fever. Neonates may also manifest with only non-respiratory symptoms like fever, lethargy, poor feeding, seizures or diarrhea).
  • 15. Patients presenting with atypical manifestations [stroke, encephalitis, hemoptysis, pulmonary embolism, acute coronary symptoms, Guillain Barre syndrome, Multiple Organ 3 | P a g e Dysfunction Syndrome, progressive gastrointestinal symptoms, Kawasaki Disease (in pediatric age group)] based on the discretion of the treating physician.
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D. Testing on demand (State Governments to decide simplified modalities):

  • 16. All individuals undertaking travel to countries/Indian states mandating a negative COVID-19 test at point of entry.
  • 17. All individuals who wish to get themselves tested.
Frequency of testing :
  • A single RT-PCR/TrueNat/CBNAAT/RAT positive test is to be considered confirmatory, without any repeat testing.
  • No re-testing is recommended prior to discharge from a COVID-19 facility after clinical recovery(please refer to MoHFW guidelines), including for transfer from a COVID area/facility to a non-COVID area/facility.
  • If symptoms develop following a negative RAT test, a repeat RAT or RT-PCR should be done.
Points to be noted:
  • WHO case definition for ILI: Individual presenting with acute respiratory infection with fever ≥ 38◦C AND cough with onset within the last 10 days.
  • WHO case definition for SARI: Individual presenting with acute respiratory infection with history of fever ≥ 38◦C AND cough with onset within the last 10 days AND requires hospitalization.
  • All healthcare workers and frontline workers coming in contact with suspect/confirmed COVID-19 patients should ensure use of appropriate PPE.
  • Home quarantine for 14 days is recommended for all individuals before undergoing elective surgery to minimize chances of infection before the procedure.
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