corona test reliability

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INTRODUCTION

I have done  rapid Covid test here in Italy.

These Rapid tests are used in Italy according to pagellapolitica.it :

These are mainly antigenic tests. I never got information which of these were used here with me.

pagellapolitica.it writes about unreliabilities in the results. Like my result could be a false negative result. I read about that before.

I got terribly confused reading news around the world. Like

www.nepalitimes.com that writes “Nepal’s decision to use rapid diagnostic kits for mass testing may actually be putting more people at risk” writes  Nepal should have gone directly for PCR like Korea and other countries instead of RDTs.

I decided to figure out what rapid test (RDT) really are and why there and risc for false results and when..

INDEX

Test Types

• PCR (Polymerase Chain Reaction, a laboratory test that shows if you have the disease). (ed. Detects corona RNA)
are highly sensitive and excellent for diagnosing acute infection,
they are expensive and require the use of special reagents, equipment and specially trained clinical laboratory scientists, all of which have been stretched thin during the pandemic so far. (

• RDT (Rapid Diagnostic Test)
There are two kinds of RDT:

1. Antigen test or  RAD (Rapid antigen detection) (ed. Detects corona proteins recognized by antibodies) Are cheaper to produce than PCR tests and can be performed very quickly, making them an option worth considering as a screening tool. (
2. serological test, a rapid blood test that shows if you have IgA, IgM, IGG antibodies). ( www.lifebrain.it )
Is useful for determining if someone had a previous SARS-CoV-2 infection, but since it takes 1-2 weeks for antibodies to develop, it is not recommended for the diagnosis of acute disease. (
• ELISA (Enzyme Linked Immuno Sorbent Assay, a laboratory analysis of blood showing the amount of antibodies)

A doctor of Spalanzani in Rome confirm that these 3d generation rapid tests are now secure.

PCR and Antigen Testing in COVID-19

(American Society of Microbiology  asm.org )writes:

Antigen tests While molecular tests can be performed in real-time, supply chain and throughput challenges have made this unrealistic during the COVID-19 pandemic. Implementing antigen testing in the COVID-19 testing algorithm could reduce strain on laboratories and reserve molecular testing for situations where high test sensitivity is required. The advantages and disadvantages of antigen testing for SARS-CoV-2 need to be considered to determine if and when it is a reliable method for COVID-19 diagnosis.

• Antigen testing is cheap and fast.
• Antigen testing may be a useful public health tool. Since antigen tests are generally considered very accurate when they are positive, they may be helpful in quickly identifying highly infectious individuals within a community. However,
it is important to note that antigen test performance in areas with low disease prevalence may be poor and data on test performance in asymptomatic individuals are limited. Since antigen tests are more likely to be positive when a person has a higher viral load,
super-spreader events or outbreaks may be prevented by identifying these individuals early and isolating them.
• Potential for use in the point-of-care setting. The rapid nature of antigen assays, as well as less reliance on expensive equipment and reagents, make them good candidates for point-of-care testing. This may reduce the burden of testing on laboratories and provide rapid results at the location where the patient is tested. …

• Lower sensitivity than PCR tests. Antigen tests are not as sensitive as PCR tests and false negatives pose a real problem. A negative antigen test should always be treated as presumptive, but can still give the patient and care provider a false sense of security. These tests may not be appropriate in settings where a positive result cannot be missed, such as hospitals or settings with high-risk patients or staff.
While they occur less frequently with this test type, false positives are also problematic
• Less expert interpretation in point-of-care settings. Although point-of-care testing is convenient, it is important to remember that the test is often performed and interpreted by healthcare professionals that are not trained in clinical laboratory science. Appropriate messaging around the interpretation of results is imperative, including the possibility of false negative and false positive results, and the continued use of public health measures, such as masking and distancing, are essential.
• Limited evidence on performance and use. There is very little literature available …
• Laboratory space, supplies and staff are still required.

Read more at (Source: asm.org )

sensitivity and specificity

Each test for Sars-CoV-2 – be it molecular, serological or antigenic – has in fact two main characteristics: sensitivity and specificity.

Sensitivity corresponds to the proportion of positives to the new coronavirus correctly identified as such: the higher the sensitivity of a test, the lower the likelihood of incurring false negatives (i.e. people who according to the test are not infected, but who in actually they are).

Specificity, on the other hand, corresponds to the proportion of negatives that are correctly identified as negative for the virus: the higher the specificity of a test, the lower the probability of incurring false positives (i.e. people who according to the test are infected, when in reality they are not I am). Read more in pagellapolitica.it

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False results – when

I found two youtubes that partially explains the risks of false results.

To understand the unreliability of covid 19 testing it is important to understand how the body react on a virus infection like corona infection.

Body immune responses

To explain this, Daniel Lewis Gerard Medinger uses information from aForbes article was published on May the 27th written by William Haseltine

The body typically has two major immune responses:

1. an antibody response is also known as a lymphoid response and
2. the cell-mediated response also known as a myeloid response

What is this myeloid response?

Myeloid cells is the collective name of Granulocytes and Monocytes. They are differentiated descendants from common progenitors derived from hematopoietic stem cells in the bone marrow.  ( www.sciencedirect.com )

• Myeloid cells attack the virus and the infected cells directly
• some myeloid cells engulf and destroy virus particles.
• others killed infected cells directly
• and others still induce a protective inflammatory response by the release of compounds called cytokines
( from Greek “κύτος” kytos “cavity, cell” + kines, from Greek “κίνησις” kinēsis “movement”. Wiki

What is it that the SARS-virus is doing differently than other coronaviruses to have this effect?

SARS-virus affects the immune response in two different ways:

• The lymphoid pathway is muted
• the myeloid response becomes hyperactive.

This is why some people who recover from Covid-19 have very low, sometimes undetectable levels of anti-SARS-2 antibodies, and others have undetectable levels of “neutralizing” antibodies capable of the inactivating virus in laboratory experiments….

A hyperactive myeloid response, on the other hand, can result in the famous cytokine storm associated with the rapid decline and death of Covid-19 patients.” ( www.forbes.com )

In dampening the antibody response to infection and ramping up production of chemokines, SARS-2 is amplifying what happens to us naturally as our immune systems age. While our ability to mount an effective antibody and T cell response to new infections declines, the myeloid arm of the immune system becomes overactive. These features of the aging immune system account for both the decline in our response to new vaccines and to an increase in inflammatory auto-immune diseases such as rheumatoid arthritis. ( www.forbes.com )

To my feeling is that this is what we’re seeing with the people out there the one in ten still suffering brutal fatigue well after a covert infection and potentially the long tail of symptoms to all seems to kind of make sense right. But science needs more than just sense it needs evidence.

Does this mean that elder people may be more easilty get false negative serologic RDT result?

Covid and antibodies

Information from www.rockefeller.edu

So let’s take a look researchers at the Rockefeller University in New York looked at blood plasma samples from 149 patients they discovered that

The majority of the samples they have studied showed poor to modest “neutralizing activity,” indicating a weak antibody response. However, a closer look revealed everyone’s immune system is capable of generating effective antibodies—just not necessarily enough of them. Even when neutralizing antibodies were not present in an individual’s serum in large quantities, researchers could find some rare immune cells that make them

… In 33 percent of donors, the neutralizing activity of plasma was below detectable levels. It’s possible that for many in this group, their immune system’s first line of defense had resolved the infection quickly, before the antibody-producing cells were called in.” (Read more in www.rockefeller.edu )

Let’s look at the accuracy of the two primary antibody tests being done in the UK the Abbott test and the rosh test.

Information taken from assets.publishing.service.gov.uk
We’ll ignore the manufacturer’s figures and instead look at Public Health England’s independent tests here’s the Abbott test the specificity is very high essentially a hundred percent.

This means that the risk of false positive is negligible ie you can trust a positive result

but the sensitivity not so much 93% this means that there is a significant risk of false and negative ie if your test comes back negative.

picture starts to emerge just a question of waiting for the data until then if you’ve got any antibody test result stories you’d like to share then that starts a discussion in the comments and perhaps we can start to get a slightly fuller picture till next time.

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“The Hong Kong cocktail”

Hong Kong Doctors See Progress In Treatment Of COVID-19

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• Sources

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