The Flu and Your INR

By: Alere Staff

As a patient on warfarin, you are no more prone to getting the flu than people not taking warfarin. However, there are some facts about the flu to keep in mind.

Each year, influenza (the flu) arrives in the fall and lingers until late spring. The flu is caused by a specific strain of virus that changes from year to year and affects between 5% and 20% of the population. Symptoms can range from mild to severe, resulting in the hospitalization of ~200,000 each year. An average of 36,000 people die annually from flu-related symptoms.1

How to prevent the flu

The Center for Disease Control and Prevention advises an annual flu vaccination if you are at high risk. Frequently washing your hands with warm, soapy water is also an effective strategy to reduce flu transmission.


The flu shares many symptoms with the common cold, but has a few distinguishing indicators. Unlike most colds, the flu can cause high fever, chills, extreme tiredness, overall body aches, and diarrhea. Secondary bacterial infections can develop while you are fighting the flu since the body’s immune system is weakened. Only a doctor can determine the difference between a bacterial infection and a viral infection.

What to do if you have (or suspect) the flu

Experts recommend that you drink plenty of fluids and get plenty of rest if you have flu symptoms. Additionally, avoiding alcohol and tobacco is highly recommended.

Special Considerations

The flu shot may result in an elevation of your International Normalized Ratio (INR) test result, but you should not be from discouraged from getting one. You should communicate your desire to receive a flu shot with your physician.

Patients taking warfarin who contract the flu are at increased risk of bleeding due to the combination of reduced appetite, fluid loss, and general stress to the body. Additional blood tests, to ensure that a sick patient remains in or near the INR target range, are often recommended. Home monitors are particularly valuable for patients taking warfarin, and those taking any medicines in addition to warfarin. Since there are no signs or symptoms before a bleeding event, only an International Normalized Ratio (INR) blood test can alert you that you are at risk of bleeding.

Additionally, you should have all over-the-counter products approved by your doctor prior taking them; especially if they are herbal, natural, or holistic in nature.

  1. Centers for Disease Control and Prevention. Seasonal Influenza.
  2. Page last updated September 20, 2013.