Yet another installment of Tales from the Trenches....
Swine flu has continued to spread throughout the summer. And everyone assumes it is going to get worse over the coming months. Mind you, other run of the mill respiratory viruses are also starting to show up during the fall and winter—a.k.a. common cold viruses and sore throat viruses. So how does your doc figure out if your fever and runny nose is from a cold or the flu?
The symptoms and the patient's examination are often enough for a doctor to tease out the diagnosis of flu (those patients are sicker appearing, and usually start with higher fevers and body aches). But in the past few years, primary care doctors have started doing rapid flu tests in their offices to help confirm the diagnosis of flu.
The test is 99% accurate if the test is POSITIVE. A positive flu test means you do indeed have an influenza infection. Cool. Some of these rapid tests even differentiate between Influenza Type A and Type B, which was really important last flu season since the A strain was resistant to Tamiflu. That test helped doctors select the correct antiviral medication for a patient who was diagnosed in the first couple of days of symptoms.
But what if your rapid flu test is NEGATIVE? That's where this great test gets a failing grade. It's only accurate about 50% of the time for swine flu (H1N1 virus). Nope, that wasn't a typo. It's only right half of the time. So if you truly have a flu-like illness with a negative rapid flu test you may still have swine flu. That will make your doctor scratch her head and diagnose/treat for flu based on her clinical judgment (just like in the good old days before these tests).
These tests will get even more confusing when seasonal flu strains arrive in the coming weeks. Rapid flu tests look for Type A and Type B, they do not specifically test for H1N1 (which is one of many Type A strains). If you test positive for Influenza Type A today, we assume it's swine flu because there we aren't seeing much of seasonal flu yet. However, as winter arrives, a positive Type A test may mean swine flu H1N1 strain or seasonal Type A strain. This may be a real problem in determining which antiviral to treat with, because we won't have a definitive answer with this simple test.
Bottom line: Is it even worth it to do a rapid flu test? Today... the answer is yes, because a positive test confirms the diagnosis. But if the rapid flu test is negative, let your doc put his medical skills to the test and decide if you have flu.