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Type of Covid-19 Tests

At Costamed Medical Group, we have the following COVID-19 detection tests for you.

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Graphic

First curve: it refers to the infection by the virus. This is called the period of viremia. The second curve (soft blue): refers to the elevation of the IGM antibodies. Third curve (red) refers to the IGG antibodies. 

This shows the period, or stage of the disease in which each of the tests can detect the Covid-19 virus.

It is important that the usefulness of each test is identified for each stage of the disease. Normally, Covid-19 can have an incubation period of up to 14 days and remain infectious for up to another 21 days. This is the reason why isolation is recommended to the patient in order to avoid spreading the disease.

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Rapid Blood Test

The tests we use at our facilities are the rapid blood tests, in which immunoglobulin levels are analyzed, so the cluster of different antibodies can be measured. Our immune system, which is in charge of defending us against diseases, produces antibodies to protect us from various pathogens like bacteria, allergens, or viruses. These antibodies are different according to what they are fighting.

There are several types of antibodies:

  • Immunoglobulin A (IgA). Present in the respiratory tract, digestive system, saliva, tears, and breastmilk.
  • Immunoglobulin G (IgG). Found mainly in the blood and brings Protection against infections from bacteria and viruses.
  • Immunoglobulin M (IgM). Found in blood and lymphatic fluid. It's the first antibody that forms to fight infections.
  • Immunoglobulin E (IgE). Found in blood, but in small amounts, it's production increases when the body overreacts to allergens or when fighting a parasitic infection.
  • Immunoglobulin D (IgD). Present in the blood but in small amounts.

The rapid blood tests allow us to evaluate the clusters of these different types of immunoglobulins and to know if it is protected against the Sars COVID-19 by the development of antibodies. The antibody levels start to increase while the disease progresses.

Once an antibody is produced as a response to a specific agent, the next time this agent enters the body, the immune system identifies it and "remembers" the defense response, producing the same antibodies that were used the last time.

The rapid tests that we have analyze the IgG and IgM levels to identify the existence of active immunoglobulin (IgM) As a response to the infection in progress (Covid-19) (an acute infection). Or if there is a "memory," immunoglobulin (IgG) created against Covid-19, which will imply that you had the disease, which means you now have a defense response in your immune system.

Our fast tests are authorized by the Federal Commission for the Protection Against Sanitary Risks (COFEPRIS) issued on May 18th, 2020, in the official federation journal.

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Rapid Antigen Test

The rapid antigen test is a recently approved WHO test. It is a new type of diagnostic test for COVID-19. 

This type of test detects the proteins in the virus's protective layer, also known as antigens. 

Once detected, it is presumed that the patient has contracted the Sars CoV-2 virus and can develop the COVID-19 disease and propagate the infection. 

The antigen test is being widely used for its speed since it only takes from 20 to 30 minutes to process after the sample has been taken. 

For this test, we use a completely sealed kit that contains a long swab with which the sample is taken from the nasopharynx. Once the sample is collected, it is processed to identify the protein chains and determine the Sars CoV-2 virus's presence. The results are delivered as "Positive" or "Negative."

The rapid antigen test works better within the first 7 days of suspicious symptoms for COVID-19. After this period of time, the possibilities of delivering a false negative increase. 


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PCR Test (Polymerase Chain Reaction)

The PCR test (Polymerase Chain Reaction) is the primary
test used to detect the Sars-CoV-2 virus that causes the COVID-19 disease in humans.

The PCR test is a molecular biology lab test, and its objective is to find genetic material from pathogens that cause diseases. By taking a small sample of organic material, this material is maximized to identify a specific genetic chain of the agent.

For the Sars-CoV-2, a variant of the RT-PCR (Reverse Transcription Polymerase Chain Reaction) is performed. In this test, we do not analyze DNA, but instead the RNA of the pathogen. The RNA is analyzed with a "Reverse transcriptase," which translates into a complementary DNA.

Once this is done, it is maximized for identification. The sample is taken through a nasopharyngeal exudate by inserting a long cotton swab through both nostrils and the throat with a rotating movement.

The PCR test is highly specific and efficient at differentiating the virus from other pathogens, and it is highly sensitive even when the pathogen is in minimal quantities and the first phases of the infection.

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Sensitivity of the Tests

  • The results of our IgG test are the following:
    • Sensitivity 100%
    • Specificity 99.5%
    • Accuracy 99.6%
  • The results of our IgM test are the following:

    • Sensitivity 91.8%
    • Specificity 99.2%
    • Accuracy 97.8%
  • The results of our Rapid Antigen  test are the following:
    • Sensitivity 93.3% (98,2 % for tests with Ct values of ≤33) 
    • Specificity 99.4%

  • The PCR test is 100% trustworthy.

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Considerations to perform the Fast Blood test

  • The test must be scheduled by an appointment
  • An official result is handed over, with a quantity response, such as "POSITIVE" or "NEGATIVE."
  • The results include an interpretation guide; however, if you wish to see a physician afterward, we will gladly schedule an appointment for you.
  • A medical order is not required for you to take the test.
  • No fasting required

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Considerations for taking the Rapid Antigen test

  • The test must be scheduled by an appointment.
  • Do not smoke; use a nasal spray or nasal drops at least three hours before the sample is taken. 
  • An official result is delivered as "Positive" or "Negative."
  • If the test is "Negative," but there is a high suspicion, then the suggestion is to take a PCR test to detect the virus's DNA. 
  • You do not need a medical order for this test.

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Considerations for PCR test

  • The test must be scheduled by an appointment
  • Do not eat, drink, smoke, use nasal spray or nasal drops, use mouthwash, or brush your teeth at least three hours before taking the sample. 
  • An official test result is provided with the qualitative results as "Detected" or "Not detected." 
  • If the test is "Not detected," but it is a highly suspicious case, it is suggested that it be retaken. 
  • A medical order is not needed for the PCR test.

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FREQUENTLY ASKED QUESTIONS. IGM / IGG RAPID TEST

  • What is the IGM / IGG rapid test?

IGM antibodies are those that are produced in our body when an external microorganism is attacking our body and our immune system uses them against that microorganism to neutralize its pathogenic effect, that is why they appear during the 2nd stage of the active disease.

  • What is the IGG test for?

The IGG helps us to know whether, or not we had contact with the disease. If we had contact with the disease, we are no longer infectious because we already generate antibodies to the virus. This test only detects if we already had the disease, not if it is active.

  • What does it mean when both IGM / IGG test positive?

This means it is most likely between day 10 and day 14 of the disease. The appearance of IGM antibodies can extend for a period of up to 25 days. The appearance of IGG antibodies begins around day 10, but can remain high, up to 3 months.

  • What does it mean if IGM is positive and IGG negative?

It is in the period of the disease where the body is responding with the biggest attack against the virus with IGM antibodies. This means you are in a contagious stage of the disease, and should self isolate according to doctor’s instructions.

  • What does IGM negative mean IGG positive?

A person has the disease, but it is no longer contagious. And has more immunity to not contract COVID-19 again.

  • PCR positive and IGG positive

PCR positive means you are with actual infection and have the viral DNA in your body. It is possible to be IGG positive also, but this cannot be determined unless you have a full antibody test including IGM (which also indicates active infection.

  • PCR positive and IGM positive

Depending on the day that symptoms started, we may be in an infectious state from -14 to day 0.

The 14 days after the onset of symptoms are crucial from the epidemiological point of view to know until when the contacts that have positive PCR (have symptoms or not) until when they could be infectious, which are 21days later.

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FREQUENTLY ASKED QUESTIONS. PCR TEST

This is intended as a guideline as there is not 100% accuracy in the periods due to person-to-person variations.

  • From what moment can the PCR test detect the Covid-19 virus?

During the first period (prior to the onset of symptoms) at least 24 to 48 hours after contact. (-7) should be -7 not 24 to 48 hours

After 7 days, the virus can begin to spread to other organs of the body.

  • What does the PCR test consist of?

This test is performed using a swab that is inserted through the nose until it touches the back of the throat, where a small rotation is made to obtain a sample of mucus, or nasal discharge as this is the place where the virus has its highest concentration during the -7 and first 7 days.

  • What does this test analyze?

This test analyzes deoxyribonucleic acid, or known as: DNA. Each person, or organism has unique characteristics in their DNA (genetic identity) The test extracts DNA from the virus to identify the fraction of DNA, as Covid-19.

  • Is it the most effective test?

Yes, it is the most effective to diagnose Covid-19, in the first stage (first days) when the symptoms have not yet appeared. (-7 day after exposure)

  • When should I have this test done?

We recommend doing this test in case you have suspicions of being infected, or for those people who have been in contact with someone who has tested positive for COVID-19.

  • What is the difference of PCR and the quick antibody test?

PCR indicates if you have the infection during the first (-7 days) days when symptoms are not yet showing. Approximately one week later (0-7 days) (depending on the patient) when symptoms appear, IGM antibodies begin to rise, which are the type of antibodies detected by the IGM / IGG rapid test.

  • The PCR test is positive, but I have no symptoms. What does this mean?

You have contracted the virus and is in your body, but symptoms have not developed as you may be still in the incubation period.

  • The PCR test is positive and I have symptoms.

The incubation period is over and the body begins to respond with the presence of IGM antibodies. (Day 0)

  • If my PCR test is positive, what should I do?

Seek medical advice; early detection and correct treatment can prevent future complications of the disease.

  • From what moment can the PCR test detect the Covid-19 virus?

During the first period (prior to the onset of symptoms) at least 24 to 48 hours after contact. (-7) should be -7 not 24 to 48 hours

After 7 days, the virus can begin to spread to other organs of the body.

  • What does the PCR test consist of?

This test is performed using a swab that is inserted through the nose until it touches the back of the throat, where a small rotation is made to obtain a sample of mucus, or nasal discharge as this is the place where the virus has its highest concentration during the -7 and first 7 days.

  • What does this test analyze?

This test analyzes deoxyribonucleic acid, or known as: DNA. Each person, or organism has unique characteristics in their DNA (genetic identity) The test extracts DNA from the virus to identify the fraction of DNA, as Covid-19.

  • Is it the most effective test?

Yes, it is the most effective to diagnose Covid-19, in the first stage (first days) when the symptoms have not yet appeared. (-7 day after exposure)

  • When should I have this test done?

We recommend doing this test in case you have suspicions of being infected, or for those people who have been in contact with someone who has tested positive for COVID-19.

  • What is the difference of PCR and the quick antibody test?

PCR indicates if you have the infection during the first (-7 days) days when symptoms are not yet showing. Approximately one week later (0-7 days) (depending on the patient) when symptoms appear, IGM antibodies begin to rise, which are the type of antibodies detected by the IGM / IGG rapid test.

  • The PCR test is positive, but I have no symptoms. What does this mean?

You have contracted the virus and is in your body, but symptoms have not developed as you may be still in the incubation period.

  • The PCR test is positive and I have symptoms.

The incubation period is over and the body begins to respond with the presence of IGM antibodies. (Day 0)

  • If my PCR test is positive, what should I do?

Seek medical advice; early detection and correct treatment can prevent future complications of the disease.

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REFERENCES

Tipos de anticuerpos

2018. inglés. Sanchari Sinha Dutta. News-Medical.net

https://www.news-medical.net/life-sciences/Types-of-Antibodies-(Spanish).aspx


¿En qué difieren los análisis de anticuerpos y las pruebas diagnósticas para COVID-19?

2020. Español. William F. Marshall, III M.D. Mayo Clinic.

https://www.mayoclinic.org/es-es/diseases-conditions/coronavirus/expert-answers/covid-antibody-tests/faq-20484429


¿Cómo funcionan y en qué se diferencian las PCR y los test rápidos de coronavirus?

2020. Español. Mónica Gail. Gaceta Médica

https://gacetamedica.com/investigacion/como-funcionan-y-en-que-se-diferencian-las-pcr-y-los-test-rapidos-de-coronavirus/


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