As we all know, it is influenza season again. Here in the U.S., we are in the midst of an epidemic of "flu." This moderately severe illness affects people differently. Most people report having fever, aching and fatigue.

Beyond these well-known symptoms, there's a new one that can fool your doctor, scare you and result in expensive and needless tests: flu can lower your blood count.

At our hospital we recently saw a 41-year-old woman who came to our emergency room with cough, fever, chills, runny nose and muscle aches that hadn't improved after taking antibiotics for three days. Ordinarily, this wouldn't get you admitted to a hospital, but when our patient's routine blood profile showed a low platelet count, we were concerned enough to keep her overnight. Repeat blood tests in the morning further revealed that her red blood cell count was low, her white blood cell count was low and that her platelet count was dropping further.

Fortunately, we had also done a rapid test for influenza which confirmed that she really had influenza virus, and was showing the common, but less well-known symptom of lowered blood counts.

When all three of the major blood cell lines (red cells, white cells and platelets) are low, a disease of the bone marrow, such as leukemia, or damage to the bone marrow from some chemical is suspected. Antibiotics, for example, such as this woman was taking for the infection that had been thought to cause her symptoms, are common among the various chemicals that can damage a bone marrow. Therefore, our next diagnostic step would normally have been a bone marrow examination, an expensive and sometimes painful test. Fortunately, we had also done a rapid test for influenza which confirmed that she really had influenza virus, and was showing the common, but less well-known symptom of lowered blood counts.

We stopped her antibiotics, and she received the traditional treatment — plenty of fluids and bed rest. As she got better from the flu, so did her blood counts.

So, if you are feeling tired and achy and find yourself at the hospital, and the doctors tell you that your blood counts are low and they're concerned, tell them to do a rapid influenza test and not a bone marrow.