COVID

Covid-19 testing:

 

which, when and why?

There are now 4 types of Covid-19 tests available;

    1. PCR 

    2. Rapid antibody tests for IgM and IgG

    3. ELISA antibody tests for IgM and IgG

    4. Antigen test .  

How accurate are they?

The manufacturers quoted accuracy rates for the methods used at Atlantic Clinic are:

PCR: Specificity and sensitivity 99.999%

Rapid antibody test:

– IgM specificity 96% and sensitivity 85%

– IgG specificity 98% and sensitivity 93%

ELISA: 

– IgM specificity 97.5% and Sensitivity 82%

– IgG specificity 97.3% and sensitivity 91.2%

 

ANTIGEN:

Sensibility : 85.0 %    Specifity : 100%

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1. PCR (polymerase chain reaction): 100€

This detects the presence of genetic material from the coronavirus., and the result can be finished the same day.

 

How?  Swabs (like a long cotton bud) collect mucous from the back of the throat and nose.

Time for result: When tested in the morning, the result will be ready in the afternoon of the next working day. PCR tests can only be done Monday to Friday.

Ask for weekends emergency.

When? The test shows positive early in the disease (within a couple of days after symptoms begin).

Why? 

  1. To diagnose the illness in the early stages of the infection, or;

  2. Increasingly some countries require a negative PCR test within 3 days prior to entry to avoid the 14-day quarantine period.

Limitations: 

After recovery the PCR may no longer be detectable so it is not so useful to diagnose a previous infection.

b. The PCR may persist for some time even after recovery because of residual genetic material leading to confusion over whether a patient is still contagious.

c. The test may be falsely negative if the sample is not taken correctly, or if the virus is not present in that part of the body (it may be only in the lungs, for example).

2. Rapid antibody tests: 40€ 

This detects the presence of antibodies (the body’s defense against the virus) which are produced in response to the infection.

How? The sample is either a drop of blood from a finger prick or a blood sample taken from the vein. 

Time for the result: the result is ready in half on an hour.

When? Antibodies take at least 7 days from infection or 4 days from the start of symptoms to show up. The IgM antibodies are seen first as the disease progresses. After recovery, the IgM disappears and IgG persists.

Why? 

  1. It is the quickest and cheapest test.

  2. It is most useful for those who have had no symptoms, or symptoms some time ago, (a minimum of 4 days) and would like to know if:

  •  You have had the disease in the past and have recovered, or;

  • You are currently infected and what stage of infectivity or recovery you are in.

Limitations

Not useful for diagnosis in the early stages of the disease (PCR is better).

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3. ELISA antibody test (enzyme-linked immunosorbent assay) 65€.

This also detects antibodies but uses more sophisticated techniques and needs skilled technicians. It may be more accurate than the rapid test.

How?  A blood sample is taken from the vein. 

Time for result:  the result are ready the same day.(about 3 hours)

When? As with the rapid test, the antibodies take at least 7 days from infection or 4 days from the start of symptoms to show up. 

Why? It is often used to confirm a rapid antibody test result that is in doubt.

Limitations

  1. It is more expensive than the rapid antibody test and takes longer to get the results.

  2. Not useful for diagnosis in the early stages of the disease (PCR is better).

4. Antigen test.  45€

This test detects the protein S from the surface of the virus and study the viral load of the virus alive.

How? : Swabs (like a long cotton bud) collect mucous from the back of the throat and nose.

Time for result:  The result will be in 30 minutes with also a certificate if you need it for travelling.

When?: When you have symptoms or you think you had a contact with a covid positive person (is necessary 5 days since the contact).

Why? : To diagnose the illness in the early stages of the infection, or in case you need it for travelling.

Limitations:

This test needs a sufficient viral load for been detected, so if you haven’t got symptoms, is necessary to wait 5 days to do the test. If you want to know before these days, you must choose a PCR test.

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