COVID-19 Update: Finger Prick COVID-19 Blood Tests
Several days ago, the Therapeutic Goods Administration (TGA) approved the use of a Point of Care (POC) serology test for COVID-19 purposes. The finger prick blood test looks for antibodies, which are a protein made in your bloodstream to fight infections such as COVID-19. The finger prick test returns a result in as little as 15 minutes. It is also much cheaper than the alternative Oral Swab PCR test.
On initial review, many employers may be led to believe that the use of this new finger prick test, may help them to better screen their workforce for COVID-19. However, this is certainly not the case.
The finger prick test is designed to detect IgG and/or IgM antibodies to COVID-19 (SARS-CoV-2). In layman terms, the test determines if the individual has an elevated level of immune response to fighting a COVID-19 infection, rather than detecting the actual COVID-19 virus (as done with Oral Swab PCR test).
It takes time for our bodies to make the IgG and IgM antibodies, so people can already have the COVID-19 virus and be spreading the infection to their colleagues and family before we can detect their antibodies using the finger prick blood test.
Whilst the test is very useful in determining if someone does have COVID-19, it is important to properly understand that a negative test does not mean you do not have COVID-19 as it takes several days for the body to develop the antibodies (IgG and/or IgM) which the finger prick test measures.
The actual test can be performed by a trained first aider, paramedic, allied health clinician or nurse but the interpretation of the result must be by a Medical Professional. Interpretation of the results requires an adequate understanding of the immunology underpinning the time course of the IgM and IgG antibody response to the SARS-Cov-2 antigen as well as an adequate understanding of the COVID-19.
Therefore, it is not recommended that workplaces use the COVID-19 finger prick blood test as a method of screening employees who are shedding the virus and may infect others within the workplace. KINNECT recommends workplaces continue to utilise a non-invasive workforce screening approach encompassing temperature checks, symptom screening and a health declaration. Should you require assistance with preparing your workforce screening approach, or would like KINNECT to provide an onsite workforce screening service at your workplace, please contact us.
The Royal College of Pathologists of Australasia (RCPA) advises against COVID-19 IgG/IgM rapid tests for the detection of early COVID disease
The Royal College of Pathologists of Australasia (RCPA) supports the use of molecular tests for SARS-COV-2 and advises against the use of serological COVID-19 IgG/IgM rapid tests, such as a pin prick blood test, to detect early COVID disease.
President of the RCPA, Dr Michael Dray said,
“The IgG/IgM tests have a fundamental limitation; they rely on the detection of antibodies made by the patient in response to SARS-COV-2, they do not detect the virus. Patients may only make antibodies to COVID-19 infection a week to 12 days after they first become sick, therefore, if doctors rely on these rapid tests early in the disease, their diagnosis will be wrong.”
The graph below demonstrates the difference between the level of IgG and IgM antibodies and the virus titre, in relation to the incubation period for COVID-19.
The RCPA states that:
- Molecular testing on a single throat with deep nasal swab is the current test of choice for the diagnosis of acute COVID 19 infection;
- COVID-19 IgG/IgM rapid tests have no role to play in the acute diagnosis of COVID-19 virus infection, and most importantly;
- COVID-19 IgG/IgM rapid tests will miss patients in the early stages of disease when they are infectious to other people.
“The RCPA therefore recommends that the new IgG/IgM tests are not used to screen for early infection, and that current Polymerase Chain Reaction (PCR) tests remain as the primary testing method for COVID-19. Whilst these new antibody tests may have a place in detecting unrecognised past infection and immunity, that role still needs to be rigorously evaluated.
“Most importantly, from a public health perspective, COVID-19-positive patients are infectious to other people early in infection when the COVID-19 IgG/IgM tests are giving false-negative results. False negatives would have serious risks of incorrectly reassuring people and therefore increasing the spread of infection within the community.
“Furthermore, elderly or immunocompromised patients may take some time to develop anti-SARS-COV-2 antibodies, and some may never develop antibodies. Reliable detection of IgM antibodies early in infection is also problematic due to cross-reactions resulting in false-positive results. In sharp contrast, the basic strength of molecular tests is that they directly detect gene sequences of the virus in the early stages of infection when the patient is infectious,” said Dr Dray.
Australia is among the world leaders for the number of SARS-COV-2 molecular tests performed per 100,000 population, with more than 250,000 undertaken in Australia so far. New Zealand pathology laboratories are also performing large numbers of molecular tests, with over 1,770 tests performed per day currently.
The RCPA Quality Assurance Program (QAP) recently introduced one of the first quality assurance programs for SARS-COV-2 in the world. This program will help laboratories optimise their molecular tests that have had to be developed rapidly in response to the COVID-19 pandemic.
In the early days of the pandemic, Australia effectively and rapidly developed and implemented robust national testing capacity through the Public Health Laboratory Network (PHLN). Testing is now broadly available through a range of hospital and private pathology providers, providing additional valuable support to Australia’s response to this public health emergency.
“The Therapeutics Goods Administration (TGA) requires that all SARS-COV-2 tests kits, both molecular and antibody-based, are subject to an effective evaluation process in Australia, this is especially important during this the COVID-19 emergency where the risk to the community of a false negative test is very high.
“It is encouraging that further review and assessment of the antibody tests has been commissioned by the TGA. The RCPA and its Fellows look forward to working with the TGA and other stakeholders to determine the best use of these COVID-19 IgG/IgM rapid tests in the Australian setting. By doing this, we will be able to safeguard Australia’s world-class testing capability for COVID-19 and ensure that the highest quality testing technology is available to support the Australian community. The College also looks forward to providing similar assistance to the authorities in New Zealand,” said Dr Dray.