Why get a Flu test?

Rapid flu tests can tell you in about ten minutes if you have the flu; why don’t doctors use these all the time, instead of wasting your time with more questions or examining you?

POSITIVE flu tests are GREAT, and yes, they speed up our assessment. We STILL need to examine you to see, for example, if your cough is aggravated with wheezing in an asthma-like response (because that involves an additional, different treatment) or if it sounds like you have developed a pneumonia (either directly from the influenza virus or as a secondary bacterial infection)-again, different treatment.

A NEGATIVE flu test, however, is not so great. Why? Short answer- a positive flu test is nearly always accurate, but a negative flu test might be wrong.

Detailed answer: Rapid flu tests have evolved each year, and current tests are EXTREMELY SPECIFIC, meaning if the the test shows POSITIVE, there is a 99% chance you are truly infected with influenza. However, these tests are good but NOT fabulously SENSITIVE, which means they fail to detect the flu anywhere from 10-25% of the time (or greater, depending on the brand, the technique of the clinician obtaining the swab and the patient’s tolerance of the swab being appropriately swirled and held for 5-10 seconds relatively deep inside your swollen, tender, runny or stuffy nose.)

Why do doctors even use these tests if they are not super sensitive? Because it affects our treatment plan. If we have confirmation that someone has the flu (with a positive test), then we can feel generally more confident in NOT prescribing an antibiotic, and limit our conversation to pros/cons of taking an antiviral medication as well as medications for symptomatic relief. This step greatly reduces unnecessary antibiotics, which is critical in an era of increasing antibiotic resistance.

ALSO, POSITIVE TESTS LIMIT the SPREAD of FLU: Knowing a patient definitely has the flu helps doctors advise them about returning to work/school/activities, since we know flu stays infectious for up to a WEEK. Not to mention BOSSES, PROFESSORS, COACHES, etc. tend to be more understanding when everyone is clear you have “INFLUENZA TYPE A”. We all trust the certainty of such diagnoses rather than hearing we’ve got “a respiratory or viral infection.” Finally, patients KNOWING for sure they have FLU changes behavior, leading to better self-care and self-imposed quarantines (rather than telling themselves to power through it, meanwhile infecting everyone around them.) PLEASE STAY HOME at least several days, and until you are fever-free for at least 24 hours!

If you had the flu vaccine, will that affect your rapid flu test? If you had a shot- no. If your flu vaccine was the intranasal spray, there is a chance that you could have a false positive test. Studies have shown that in the first several days after receiving the nose spray vaccine, people may test positive for the flu (even though they are not infected.)

So if your test is negative but your doctor THINKS you have the flu, then what? Answer: your doctor uses her judgment, because diagnosing the flu does not REQUIRE a positive test. The CDC encourages treatment for all HIGH risk individuals with SUSPECTED (or confirmed) flu with antiviral medications.

Who is at “high risk”? Some are obvious- anyone hospitalized, patients in nursing homes, and people with immune problems, significant chronic problems (lung or heart disease, for example) or with severe illness such as pneumonia. However, HIGH RISK also includes all otherwise healthy children under the age of two years, adults over the age of 65, and women who are pregnant or have just delivered their baby within the past two weeks. There are also other less common subgroups that are high risk such as people who are very obese (BMI >40), American Indians or Alaska natives, and youth under 19 who are on chronic aspirin therapy.

Does everyone need to take the ANTIVIRAL medication? No-otherwise healthy, active adults who test positive for the flu should have a DISCUSSION with their physician about taking the antiviral medications. When taken within 48 hours of the onset of flu symptoms, these drugs have been shown to decrease the duration of the flu by one or two days…which may make a big difference to a student, parent or employee. However, these medications are not without side effects, and for some people, they may aggravate flu symptoms- particularly nausea. In controlled studies, the antiviral medications only cause about 10% more nausea/headaches/fatigue than placebo, but there is no doubt that in a minority of patients, the medicine causes more side effects than they are worth. However, since you have the FLU when you are taking the medications- you already likely HAVE nausea, headache, fatigue, etc- so it is often difficult to sort out. In my family, half of us can tolerate the antiviral medications with zero problems, and half…barely keep the pills down long enough to know.

WAIT, should EVERYONE with symptoms get a rapid flu test? NO. These tests are not free, and again, not perfect. Especially when flu is rampant in our area, clinical judgment is enough to make the diagnosis, especially in otherwise healthy individuals.

BOTTOM LINE: If you have flu symptoms, get to the doctor as soon as possible (especially if you would consider taking antiviral medications), and understand that a positive test is REALLY positive, but a negative test does not definitely rule out the possibility of the flu.

AND…PREVENTION! GET YOUR FLU SHOT NOW to reduce your chance of getting the flu (or to at least minimize your symptoms if you do catch it.)

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