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What is a Swine Flu test?

A swine flu test, also known as the H1N1 test, is a blood test that detects swine flu virus (H1N1 flu virus strain). A swine flu test helps distinguish the cause of influenza and diagnose H1N1 virus as a cause of the flu. It is carried out in two ways: 

  • Detecting the presence of viral antigen (virus fragments)
  • Detecting the virus in phlegm (mucus) or in a tissue swab from the nasopharynx.

Swine flu means flu or influenza of pigs, although this virus H1N1 infects pigs, birds as well as humans. This virus does not spread through eating pork but by coming in direct contact with an infected person. Common symptoms associated with swine flu include fever, cough, sore throat, body ache, lethargy and fatigue. All these symptoms may go on up to a week. Sometimes, when the infection is severe, it causes difficulty in breathing and even respiratory distress; however, in majority of patients, the symptoms are milder and self-limiting.

  1. Why is a Swine Flu test performed?
  2. How do you prepare for a Swine Flu test?
  3. How is a Swine flu test performed?
  4. What do Swine Flu test results indicate?

Swine flu test is performed to distinguish the cause of flu and diagnose H1N1 viral infection when symptoms of flu are present. This test is usually performed within three days of the onset of flu symptoms and provides rapid results in detecting viral antigen in the blood.

The signs and symptoms of flu include:

In severe cases or in hospitalised patients, symptoms of respiratory distress (difficulty in breathing, gasping for breath, etc.) are also seen. Swine flu test is more commonly performed for patients who are:

  • Hospitalised
  • Have weak immunity (on immune suppressive medicines or suffering from HIV infection etc.)
  • At high risk for developing complications
  • Aged

A swine flu test is also the first test prescribed for ruling out H1N1 infection during the outbreaks of influenza or respiratory illness.

No special preparations are needed for this test.

It is a simple test that takes less than five minutes. An experienced laboratory specialist collects a blood sample from a vein in your arm by inserting a small needle into the vein. A small quantity of blood is withdrawn into a sterile vial or a test tube. A momentary pricking pain is felt when the needle injects but the procedure itself, is otherwise, risk-free.

Some people may experience light-headedness and bruising at the site of injection. However, at most times, these symptoms disappear quickly. Rarely, an infection may occur at the site of blood withdrawal.

Normal results: An absence of H1N1 is considered normal, which indicates that swine flu is not the reason for the ongoing symptoms.                 

A negative result does not necessarily mean an absence of H1N1 strain; sometimes, it means the presence of an insufficient viral load to be detected or poor specimen collection.

Abnormal results: Presence of  H1N1 antigen in blood indicates an ongoing infection with swine flu virus.

Swine flu test holds more significance for children; elderly; immunocompromised patients; or those with pre-existing lung diseases, such as chronic bronchitis and interstitial lung disease, as they are more prone to complications, such as sepsis, pneumonia, encephalitis etc.

The accuracy of this rapid antigen test is about 70%, which means even if the test is negative, the possibility of having swine flu remains; thus, a thorough clinical history, complete blood count and chest X-ray are mandatory, apart from swine flu antigen test.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. This information is purely from an educational perspective and is in no way a substitute for medical advice from a qualified doctor.

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  1. Center for Disease Control and Prevention [internet], Atlanta (GA): US Department of Health and Human Services, Influenza Signs and Symptoms and the Role of Laboratory Diagnostics
  2. Center for Disease Control and Prevention [internet], Atlanta (GA): US Department of Health and Human Services, Influenza Virus Testing Methods
  3. National Institute of Allergies and Infectious diseases [internet]: National Institute of Health. US Department of Health and Human Services; Influenza
  4. Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
  5. Center for Disease Control and Prevention [internet], Atlanta (GA): US Department of Health and Human Services, What To Do If You Get Sick: 2009 H1N1 and Seasonal Flu
  6. Center for Disease Control and Prevention [internet], Atlanta (GA): US Department of Health and Human Services, Influenza Diagnostic Testing During the 2009-2010 Flu Season