Friday, September 29, 2023

Is There A Blood Test For Flu

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Types Of Influenza Tests

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The first step in diagnosing influenza is almost always a physical examination that includes a review of any active flu-like symptoms. During seasonal flu epidemics, additional testing beyond a physical exam may not be needed to diagnose influenza.

When other tests are needed, they focus on identifying signs of an influenza infection. There are several different tests that can check for the presence of an influenza virus. The choice of which test to prescribe depends on the purpose of testing, how quickly results are needed, test availability, and laboratory capabilities.

One important way that influenza tests can be categorized is based on where the analysis is conducted:

  • Rapid, point-of-care tests, sometimes called rapid influenza diagnostic tests , are able to determine whether the test is positive or negative without sending the sample to a lab. These tests usually provide results within 10 to 30 minutes. The design of these tests allows them to be used in many settings including doctors offices, health clinics, and pharmacies.
  • Laboratory tests require that the sample be analyzed using equipment or methods that require the use of a medical lab. These tests often take several hours to complete and are not as widely available as rapid tests.

Another important way of categorizing tests is based on how they detect signs of an infection:

Antigen testing can also be done in a laboratory. Laboratory-based antigen testing can take longer but may provide more accurate results.

How Colds And The Flu Are Diagnosed

Colds and the flu are primarily diagnosed by your symptoms, but healthcare providers will sometimes also use a rapid test or other lab tests to confirm a flu diagnosis. Figuring out what, specifically, is behind your symptoms can better help you and your practitioner develop a treatment plan.

How Are Samples Collected For Rapid Influenza Diagnostic Tests

There are two main methods of getting a sample for testing:

  • Swab test: Your doctor will use a special swab to take a sample from your nose or throat.
  • Nasal aspirate: Your doctor will inject a saline solution into your nose and then remove a sample with gentle suction.
  • These samples are checked for the presence of viral particles. A positive result means that the rapid influenza diagnostic test detected the influenza viral particle in the fluid. However, this does not necessarily mean the virus is alive and thriving in the body because it may also detect a dead viral particle.

    • A positive result is most likely a true positive result if the respiratory specimen was collected close to illness onset during periods of high influenza activity.
    • A negative result simply means that the RIDT did not detect an influenza viral antigen and could be a false-negative.

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    Understanding A Rapid Flu Test

    The rapid flu test helps your doctor determine whether your symptoms are caused by the influenza virus. A flu test involves taking fluid samples from your nose or throat and analyzing them in a lab. Test results are usually available within 15 to 20 minutes. If you test positive for the flu, you can be treated by your doctor immediately to reduce flu symptoms. Evidence suggests that the rapid flu test may not be as accurate as other flu tests some people still have the flu despite negative test results.

    The purpose of a rapid flu test is to determine whether you have the flu so you can take advantage of early treatment. Early treatment can prevent symptoms from peaking in severity and from contributing to more serious health problems and medical conditions.

    How Do They Decide What Strains Are In The Vaccine Each Year

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    Each year, the flu vaccine, containing inactivated virus, is targeted to protect against the expected strains, based on the observations and experience of healthcare practitioners and scientists. Healthcare providers and researchers carefully track the influenza virus circulating worldwide and try to anticipate the strain that will eventually appear locally the next season.

    As influenza travels through communities around the world, it undergoes spontaneous changes that allow it to evade the protective antibodies formed from previous infections and vaccinations. The amount of “antigenic drift” varies from year to year. Bigger antigenic drifts, known as “antigenic shifts,” result in more severe illnesses since more people will be susceptible to the virus.

    Sometimes the flu strain will have significant antigenic drift during the season so that the virus will appear slightly different to the body’s immune system, decreasing the effectiveness of the vaccine’s protection. Or, the flu that predominates may end up being an unexpected strain, not the ones that the vaccine was developed to protect against.

    Usually, in these cases, the vaccination will at least lessen the severity of the infection. In individual high-risk patients , healthcare practitioners may bolster the protection by prescribing antiviral treatments before the person gets sick to provide short-term protection while influenza moves through the community.

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    Are Test Results Accurate

    At-home influenza tests are widely used to identify infections, but, like any medical test, not 100% accurate. Results are dependent on the following factors:

    Since multiple factors can be involved in interpreting the accuracy of influenza testing, it is best to discuss your at-home flu test result with a doctor who can explain how these factors apply in the context of your specific test outcome.

    Similarities Between The Symptoms Of The Flu And Covid

    The flu and COVID-19 are different viruses. They’re very contagious and have similar symptoms. This can make it hard to tell the difference between the flu and COVID-19 when symptoms appear.

    If you start to develop symptoms, follow the same precautions taken for COVID-19.

    This year is more important than ever for everyone 6 months and older to get the flu shot. This will help prevent the flu and flu-related complications. Preventing the flu will also help reduce stress on the health care system during the COVID-19 pandemic.

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    Become A Fluwatch Sentinel Practitioner

    The sentinel influenza-like-illness surveillance system is FluWatch’s primary source for outpatient influenza monitoring data in Canada.

    Physicians, nurse practitioners and registered nurses who are involved in primary care are welcome to become FluWatch sentinel practitioners.

    Learn more about the FluWatch sentinel practitioner program or e-mail to sign up.

    Is There Anything Else I Need To Know About A Flu Test

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    A new flu vaccine is made each fall. The Centers for Disease Control and Prevention recommends the vaccine for most people 6 months or older. It is especially recommended for people in high-risk groups, such as young children, adults over the age of 65, and individuals with pre-existing conditions, such as asthma or heart disease. If you have questions about the flu vaccine, talk to your health care provider.

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    Laboratory Methods And Clinical Data

    Nasopharyngeal swabs were prospectively collected and tested. The colloidal gold method was applied immunochromatography and a double-antibody sandwich to detect influenza A/B antigens by influenza A/B viral antigen detection kit . Preservative solution containing the dissolved sample was added to the well in the test card, and chromatography was performed after 1520min to detect the influenza antigens.

    The nucleic acid test was used for a definitive diagnosis of influenza. The specimens were delivered to the laboratory of Beijing Haidian District Center for Disease Control and Prevention following a standard institutional protocol used at the study center, which is a national sentinel surveillance hospital. The influenza A/B nucleic acid assay kit, H1N1 influenza A/seasonal influenza H3 nucleic acid assay kit and the Victoria/Yamagata influenza B nucleic acid test kit were used and assayed for each sample on the ABI 7500fast real-time quantitative PCR system.

    Data on demographics , clinical presentation were collated. Medical history , routine blood test results , and influenza colloidal gold test were included for analysis.

    Is There Anything Else I Should Know

    Treated or untreated, most influenza infections will go away within one or two weeks, although fatigue and a cough may last a while longer. A few people, however, may develop serious secondary complications. These complications often arise just as influenza symptoms are fading.

    Anyone is susceptible to complications from the flu, but the very young, the elderly, and people who are immunocompromised or who have pre-existing lung disease are most affected. Complications such as pneumonia, sepsis, and encephalitis can be very serious and may require immediate medical treatment.

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    How Do You Know If You Need A Flu Test

    Your need for a flu test will come down to the symptoms to present to your doctor, and how they decide to diagnose those symptoms. The most common signs and symptoms of the flu, per the CDC, usually include:

    • Fever and chills
    • Cough
    • Fatigue or tiredness
    • Vomiting and diarrhea

    You may realize that the symptoms listed above are also very common to those seen with COVID-19and if your doctor decides to test for that first, and it comes back negative, they will likely move on to a flu test, Robert L. Murphy, MD, a professor of infectious diseases at Northwestern Medicine Feinberg School of Medicine, tells Health.

    Is There A Test That Can Detect Both Flu And Covid

    Blood Test Tube For Influenza Virus Testing Stock Photo

    Yes. There is a test that will check for seasonal flu type A and B viruses and SARS-CoV-2, the virus that causes COVID-19. This test is being used by U.S. public health laboratories for surveillance purposes. Testing for these viruses at the same time will give public health officials important information about how flu and COVID-19 are spreading and what prevention steps should be taken. The test will also help public health laboratories save time and testing materials, and to possibly return test results faster.

    The Food and Drug Administration has given CDC an Emergency Use Authorizationexternal icon for this new test. Initial test kits were sent to public health laboratories in early August 2020. CDC will continue to manufacture and distribute these kits.

    More information for laboratories is available.

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    Will My Health Care Provider Test Me For Flu If I Have Flu

    While your doctor may test you for flu, not everyone who goes to the doctor with flu-like symptoms will be tested. After evaluating you, your doctor may choose to diagnose you with flu without the need for testing based on your symptoms and his or her own clinical judgement.

    Please visit diagnosing flu for more information.

    When Is It Ordered

    Flu tests are mostly ordered during flu season , especially when a person is hospitalized, has a weakened immune systems, or is otherwise at an increased risk of serious complications. Testing is usually ordered within 3 days of the onset of signs and symptoms, such as:

    • Headaches
    • With some flu strains, diarrhea and vomiting

    When influenza has not yet been documented in the community, a healthcare practitioner may order a rapid flu test both to document the presence of influenza in the area and to help diagnose an individual’s current illness.

    Testing may be ordered during outbreaks of respiratory illnesses when influenza is the suspected cause.

    Sometimes testing may be done when someone who died had a severe, acute illness and influenza was the suspected cause.

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    Appropriate Use Of Antimicrobials

    Using rapid and point-of-care influenza tests may help clinicians more appropriately prescribe antibiotics and antiviral medications.58,59,65,66

    Two small 2014 studies examined the effect of positive point-of-care test results on physician-prescribing of antibiotics.65,66 Both concluded that point-of-care tests may help reduce the use of antibiotics. Similarly, the retrospective analysis of 4.9 million US emergency department visits found patients received fewer antibiotics if they tested positive for influenza by rapid antigen testing.59 However, in its 2014 systematic review of rapid viral testing of children presenting to the emergency department with acute respiratory infection, the Cochrane Collaboration found no evidence to support the use of routine rapid testing to reduce antibiotic use in children.58

    How Is A Flu Test Performed

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    All flu tests require a respiratory sample. This can include samples from:

    • Your nasal cavity with a swab.
    • Your nasal cavity through a wash or aspirate, meaning your healthcare provider injects a saline solution into your nose and removes the sample with gentle suction. This collection method is sometimes used on very young children.
    • The upper part of your throat with a swab through your nose.

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    What Do The Results Of A Flu Test Mean

    • Positive result: A positive result means that the test detected influenza viral antigen or RNA.
    • Negative result: A negative result means that the test didnt detect any influenza viral antigen or RNA.
    • Invalid result: If your test reveals an invalid result, it means there was an error in the testing. This could mean an issue with the sample collection or the test itself. Youll need to take another test.

    Should I Get A Flu Shot

    The Centers for Disease Control and Prevention recommends that everyone 6 months old and older get a flu shot each season. In particular, people who are at high risk of complications from the flu should receive the vaccine. These include young children, the elderly, residents of nursing home and other long-term care facilities, pregnant women, and people with pre-existing conditions such as asthma, COPD, heart disease, and liver or kidney disorders.

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    The Real Reason For Withdrawing The Eua Request

    The first Facebook post we referenced quoted from and linked to a that informed labs that as of Dec. 31 the agency would withdraw its emergency use authorization request for the CDC 2019 or, for short, the CDC 2019-nCoV RT-PCR.

    It is standard practice for the Food and Drug Administration to issue temporary emergency use authorizations for tests and other medical products that have not yet undergone the FDAs full approval process but need to be used in an emergency to diagnose, treat or prevent serious diseases.

    The FDA issued the EUA for the CDCs 2019-nCoV RT-PCR in . At that time, no other tests were available in the U.S. to determine whether someone had COVID.

    But its important to remember that what the CDC developed and submitted for its EUA request was not a tangible product but rather a protocol for how to test for COVID, said Susan Whittier, a professor of pathology and cell biology at Columbia University Irving Medical Center. That means the CDC wrote out directions specifying which reagents were needed to test the laboratory samples for the presence of the COVID virus. The CDC does not distribute COVID tests.

    Its not like they have a test that laboratories can purchase. We borrow their protocol and use the reagents that they say, said Whittier, who recently retired as director of the clinical microbiology lab at Columbia. So withdrawing the EUA request just means that protocol will no longer be available.

    Polage agreed.

    When Should I Get An At

    Blood Test Tube For Influenza Virus Testing Stock Image

    There are no strict guidelines or clear recommendations for when to take an at-home flu test.

    In general, flu testing is only conducted when you have symptoms that could be caused by an underlying infection with an influenza virus. Testing is most often done when symptoms are significant or when you are at higher risk of flu complications because of your age, coexisting medical conditions, or pregnancy.

    A flu test is often not necessary if you have only mild symptoms and flu transmission in your community is high. In these cases, testing may not be needed because it would not change the way you are treated.

    If you have flu-like symptoms or are concerned about possibly having the flu, you should talk with a doctor. Since there are multiple factors involved in determining whether a flu test is appropriate, the doctor can address whether testing, including at-home testing, is recommended in your situation.

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    Why Do You Need It

    When your doctor finds the flu virus, they can give you antiviral drugs early on. This is when they work best. If you get diagnosed early — within 48 hours after symptoms show up — these drugs can ease your symptoms and shorten the illness by a day or so. After the first 2 days, though, these meds wont do much for you.

    A flu test can also help your doctor rule out giving you antibiotics. Those dont work against viral infections like the flu.

    Influenza Virus Testing Methods

    Table 1: Influenza Virus Testing Methods

    Rapid Influenza Diagnostic Tests4 A and B NP5 swab, aspirate or wash, nasal swab, aspirate or wash, throat swab < 15 min.
    Rapid Molecular Assay A and B
    Immunofluorescence, Direct or Indirect Florescent Antibody Staining A and B NP4 swab or wash, bronchial wash, nasal or endotracheal aspirate 1-4 hours No
    RT-PCR7 and other molecular assays A and B NP5 swab, throat swab, NP5 or bronchial wash, nasal or endotracheal aspirate, sputum Varies No
    Rapid cell culture A and B NP5 swab, throat swab, NP5 or bronchial wash, nasal or endotracheal aspirate, sputum 1-3 days
    Viral tissue cell culture A and B NP5 swab, throat swab, NP5 or bronchial wash, nasal or endotracheal aspirate, sputum 3-10 days No
  • Serologic testing is not recommended for routine patient diagnosis and cannot inform clinical management. A single acute serum specimen for seasonal influenza serology is uninterpretable and should not be collected. Serological testing for detection of antibodies to seasonal influenza viruses is useful for research studies and requires collection of appropriately timed acute and convalescent serum specimens and testing of paired sera at specialized research or public health laboratories.
  • Clinical Laboratory Improvement Amendments of 1988.
  • NP = nasopharyngeal
  • Rapid molecular assays can provide results in approximately 15-30 minutes.
  • VTM = Viral transport media
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