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ACB Expert briefing on COVID-19 diagnosis, patient assessment and monitoring

04/04/2020 10:12:47

Association for Clinical Biochemistry and laboratory medicine (ACB) members work in healthcare laboratories to help prevent, diagnose and treat illness using their knowledge of science and their technical skills.

This expert briefing aims to clearly convey ACB members’ role in diagnosing, assessing and monitoring COVID-19 and the science behind their work to the media and public.

When did scientists first know about COVID-19?

SARS-CoV-2 (the novel coronavirus that causes COVID-19) was first described in China in late December and the first UK case was seen a month later.

What are UK clinical scientists doing to make sure COVID-19 tests are ready for roll out?

Clinical and healthcare scientists have been working hard for several weeks to procure, validate (make sure a test accurately measures what it is supposed to measure), and roll out these tests. This has involved rapid redeployment and training of staff to cover extended shifts.

How do clinical scientists test whether someone has COVID-19?

There are three main ways of testing for SARS-CoV-2 (the novel coronavirus that causes COVID-19):

1. Molecular detection of viral genetic material: the gold standard

How good is the test?
These tests, known as nucleic acid amplification tests (NAAT, also called PCR; polymerase chain reaction), are highly accurate when identifying those with and without the disease.

Is the test ready for roll out?
NAAT or PCR tests could not be developed, or scaled up until fundamental information about the virus was known, i.e. its genetic code. Reference laboratories around the world, including in the UK, were amongst the first to develop these tests with commercial manufacturers soon following suit. Most manufacturers, including the largest producers, are based outside the UK. Additional consumables, such as tubes and pipettes also need to be sourced in large quantities from overseas. UK laboratories have been working hard to do this for several weeks, as have laboratories all over the world.

Is the test safe for clinical scientists to use?
The SARS-CoV-2 virus has been designated as a Hazard Group 3 pathogen by the Advisory Committee on Dangerous Pathogens. Laboratories must have appropriate measures in place to ensure the safety of their staff. Before extracting and detecting the genetic material, the virus must be inactivated so it is safe to handle. This is a complex process that requires specialist equipment and chemicals in addition to the equipment and chemicals needed to carry out the test. 

2. Detecting viral proteins from patient samples: fast but less accurate

How good is the test?
Although this test can be done quickly, it is not as good at correctly identifying those with the disease and is usually much worse at diagnosing acute infections (within 6 months of infection) as compared to the gold standard of molecular detection of viral genetic material.

Is the test ready for roll out?
There are currently no such tests being used to diagnose COVID-19.

3. Detecting antibodies in samples from infected patients: of limited use

How good is the test?
This test is of limited use in diagnosing active viral infections, especially those caused by respiratory viruses. 

Why is this test of limited use?
Antibodies are proteins produced in the body to help the immune system get rid of bacteria and viruses. If a test detects antibodies produced by the patient’s body to get rid of COVID-19, it can only show that the patient has been infected at some time in the past. Antibodies produced early on in the infection (known as IgM) are often not able to correctly identify those without the disease and can cause false positive results. Antibodies produced later in infection (known as IgG) are often more reliable. On top of this, both types of antibody test can generate false positive results as they may detect antibodies produced to protect patients when infected by similar viruses, such as the seasonal coronaviruses that circulate annually causing cold symptoms. At the moment we do not know at what stage of infection patients with COVID-19 start to produce protective antibodies and how long the protection is likely to last for.

Is the test ready for roll out?
These tests are only just coming to the market and scientists need to make sure they accurately measure COVID-19 antibodies and give reliable results. Clinical scientists are doing this by using blood from people with confirmed COVID-19 infection and people confirmed never to have had COVID-19. Without spending time making sure the test is able to accurately detect COVID-19 antibodies, a patient who has never been infected could end up with a positive result. This scenario could lead to a false sense of security, especially in a healthcare worker or other frontline worker who is required to work in a high-risk environment. 

Assessment & monitoring of patients

How can laboratory findings help patients with COVID-19?
Analysing samples from patients with COVID-19 can help scientists see what happens in the body at different stages of the COVID-19 infection. This information is used by doctors to help them decide how treat their patients.

Studies have shown that patients with severe cases of COVID-19 have increased levels of molecules in the body produced by heart disease. By measuring the levels of these molecules in patients with COVID-19, clinical scientists can see if the condition of the patient is likely to get worse. Doctors can use these laboratory findings to improve the health of the patient by giving them treatments usually used for heart disease.  

Definitions

Clinical scientists often use the following terms in their work. These definitions may help if you go on to read more technical documents about COVID-19.

Test validity: the extent to which a test accurately measures what it is supposed to measure
SARS-CoV-2: the novel coronavirus that causes COVID-19
Test sensitivity: the ability of a test to correctly identify those with the disease
Test specificity: the ability of the test to correctly identify those without the disease

Contact: communications@acb.org.uk

Further information on diagnosing COVID-19:
http://www.acb.org.uk/whatwesay/acb_newspage/2020/04/04/diagnosing-and-testing-for-covid-19-update-from-acb-microbiology-professional-group

Further information on assessment and monitoring of patients with COVID-19:
http://www.acb.org.uk/whatwesay/acb_newspage/2020/03/23/coronavirus-and-covid-19-update-from-acb-scientific-committee

 

 

 

 

Agnes Becker

(This page is maintained by the ACB Publications & Communications Committee)


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