Covid-19 antibody test kits approved: what you need to know

UNATHI NKANJENI

Serological tests, a blood test that looks for signs of a previous Covid-19 infection, have been approved to be used as part of SA’s fight against the pandemic.

On Tuesday, the SA Health Products Regulatory Authority (SAHPRA) authorised the use of one rapid and point of care serological test kit.

Five lab-based serology tests have also been approved.

Here is what you need to know.

A serological test is an antibody test that looks for the presence of antibodies, which are specific proteins made by the body in response to infections. The test involves collecting a small blood sample from a patient by using a device that pricks their finger. The test can determine whether a person has been exposed to a particular virus.

The antibody test was approved a month after President Cyril Ramaphosa said they would be made available and would improve “community surveillance” of the spread of Covid-19 infection.

The “rapid test” kits are different from the Polymerase chain reaction (PCR) test being used in the country, said the authority. “The difference between the molecular PCR and the serology test is that the PCR tests are able to detect and diagnose whether one has been infected with Covid-19 and thus give a clinical diagnosis.

“Serology tests can detect if one has developed antibodies for Covid-19. This means the tests cannot be used for clinical diagnosis,” the authority said.

Dr Boitumelo Semete-Makokotlela, CEO of SAHPRA, warned that the serology tests cannot be conducted at home. She said they have to be administered by qualified professionals and must have been validated. They should only be used within the department of health’s surveillance strategy

“Rapid test kits cannot be used to clinically diagnose Covid-19 cases, but they may play a role in research and epidemiological and sero-surveillance studies. Rapid test kits are not recommended by the World Health Organisation for clinical diagnosis of SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) infection,” Semete-Makokotlela said.

The antibody test kits may not be sold to the public.

Health minister Zweli Mkhize confirmed the tests were now available and issued guidelines for their use.

“Today I am pleased to announce the director-general for health has issued guidelines for the use of SARS-CoV-2 antibody tests, and that SAHPRA announced its approval of several test kits, both labs based and point of care or bedside rapid tests,” he said.

“This is a very welcome development and I would like to thank the ministerial advisory committee on Covid-19 and members of the strategic management bodies in the department of health for all the hard work that has gone into ensuring antibody tests are used appropriately and effectively as we continue to battle Covid-19. It will be important to understand the limitations of antibody testing.”

According to the health department, these tests may be used to:

  • Diagnose Covid-19 retrospectively in patients who have recovered from a Covid-19 compatible illness and are negative based on results from the SARS-CoV-2 PCR Test.
  • Diagnose Covid-19 in patients who are admitted with suspected SARS-CoV-2 infection but who test negative for RT-PCR (reverse transcription-polymerase chain reaction) as an ancillary investigation. This will include children with suspected multisystem inflammatory syndrome who may test negative by SARS-CoV-2 PCR.
  • Identify past exposure to SARS-CoV-2 in individuals optimally at 21-days post-infection.
  • To assess SARS-CoV-2 vaccine responses.
  • To identify potential convalescent plasma donors.

A negative antibody test result does not reliably rule out prior SARS-CoV-2 infection. Possible causes would be:

  • Insufficient sensitivity of antibody test.
  • Acute phase testing (specifically within 14 days post-symptom onset).
  • Some patients may not form detectable antibodies, especially following asymptomatic SARS-CoV-2 infection.
  • Waning of antibodies over time, and as soon as one to two months in asymptomatic or mild cases.

A positive antibody test result does not reliably prove prior SARS-CoV-2 infection. Possible causes would be:

  • Insufficient specificity of antibody test.
  • Cross-reacting antibodies, for example those directed against other human coronaviruses.

The department said the biological significance of specific anti-SARS-CoV-2 antibodies is uncertain. This is due to a number of factors, such as the detection of antibodies that may not correlate with immune protection.

“A positive antibody test result therefore should not be regarded as proof of immunity and must not be used to reduce or abandon protective measures,” said the department.

“Antibodies detected by different assays do not necessarily represent neutralising antibodies that are assumed to be the best measure of humoral immunity and protection against infection and/or disease.”

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