Corona Virus Information and Testing Debate
To support our regular OH clients, Black and Banton have been using the Assure Tech Point-of-care (PoCT) COVID-19 serology test to test for the qualitative detection of IgG and IgM antibodies to Covid-19 in human whole blood.
Tests for COVID-19 aim to detect the causative virus, SARS-CoV-2, or an immune response to SARS-CoV-2.
The reliability of COVID-19 tests is uncertain due to the limited evidence base. Available evidence mainly comes from symptomatic patients, and their clinical role in detecting asymptomatic carriers is unclear.
The indications for conducting COVID-19 tests are constantly changing through the course of the pandemic and Black and Banton will continue to follow guidance when advising our clients on the use of any Point of Care Test Device.
The three main types of SARS-CoV-2 tests are:
Nucleic acid detection tests – using qPCR to detect SARS-CoV-2 viral (Ribonucleic acid) RNA; and
Serology tests – to detect IgM and/or IgG antibodies against SARS-CoV-2
and Antigen tests that detect proteins on the surface of SARS-CoV-2
Nucleic Acid / PCR Tests
Reverse transcriptase Polymerase Chain Reaction (PCR) tests detect SARS-CoV-2 nucleic acid (RNA). Most of these assays typically take several hours (including specimen processing time) to generate results, and require complex laboratory equipment and trained technicians. There are now some near patient SARS-CoV-2 PCR instruments available that can be used outside of a laboratory. These systems can provide quicker results but cannot do as many tests at once.
PCR tests are currently considered to be more clinically sensitive than serology assays for detecting early infections and, because they directly detect viral RNA, they are an indicator for viral shedding. The extent to which a positive PCR result correlates with the infectious state of an individual is still being determined. Clinical resolution and consecutive negative PCR tests in a previously positive individual are currently being used as criteria when considering release from isolation. However, this is changing constantly with increasing knowledge around SARS-CoV-2.
Serology Antibody tests
A variety of Point of Care (often referred to as PoC or PoCT) branded products, accepted by the Medicines and Healthcare products Regulatory Agency (MHRA) are being placed on the UK market for serology tests that utilise lateral flow immunoassay technology. However, the HMRA state that they are for professional use only.
Legally the product can be placed on the market but the MHRA does not quality approve the validity of these products.
Point of care serology tests are intended to detect IgG and/or IgM antibodies to SARS-CoV-2 from venous or finger prick blood samples that are placed on a test strip. These tests look like common pregnancy tests. Results take about 15 minutes.
There is a window period between virus infection and the production of IgM and IgG antibodies, and the sensitivity and specificity of IgM/IgG antibody tests early in SARS-CoV-2 infection is not well characterised. Antibodies will likely take between 5-7 days (or longer) to become detectable after infection with SARS-CoV-2. Because antibody tests do not detect active viral shedding, they cannot detect if an individual is infectious. Though they provide some useful information when combined with the clinical picture, a suggestive clinical picture plus a positive PoCT may be considered enough for a presumptive positive diagnosis and subsequent management.
Covid antigen test
Antigen tests detect protein on the surface of SARS-CoV-2 (the virus that causes COVID-19) directly from a sample taken with a swab inserted into the nose and throat. Because antigen tests do not amplify parts of the virus’ genetic code, they are less sensitive than PCR tests
The main advantages of antigen tests over PCR tests include their lower cost and their speed. Most antigen tests are designed to be used at the point of care, with results available in about 15 minutes.
Covid-19 Test Performance
COVID-19 is an emerging viral infectious disease. There is limited evidence available to assess the accuracy and clinical utility of available COVID-19 tests.
Due to the urgent nature of the COVID-19 pandemic, several SARS-CoV-2 tests are undergoing an expedited assessment by the UK Government to inform and guide their best use in the UK. These expedited assessments are based on the limited clinical and performance data currently available. The Assure Tech antibody test comes with a set of performance data, CE Declaration of Conformity documentation and company ISO13485 accreditation (for medical device manufacture). We have worked with our supplier in the UK for many years and they have distributed point of contact devices from their suppliers for several years.
- The antibody test result cannot be used for diagnosis of COVID-19. As with all diagnostic tests, a definitive clinical diagnosis should not be based on the results of a single test but should only be made by a physician after all clinical and laboratory findings have been evaluated.
- The ability of serology tests to accurately detect exposure to the Covid-19 relies on their sensitivity and specificity, which can vary significantly between different assays. Serology tests can be cross-reactive and detect antibodies produced in other infections. For example, less severe seasonal coronaviruses circulating in the community can induce antibodies that cross-react in a COVID-19 test to produce false-positive results. Serology tests can also sometimes miss detection of Covid-19 antibodies and give a false-negative result.
- Serology tests can also sometimes show detection of Covid-19 antibodies even when a person has not been infected and give a false-positive result.
Serology point-of-care COVID-19 tests cannot determine whether a person is infectious.
Serology point-of-care COVID-19 tests are not able to detect if a person has been recently infected (i.e. in the last week or so).
It is illegal to supply these COVID-19 point-of-care tests as self-tests or tests for home use in the UK.