How can you tell if bronchitis is viral or bacterial just by a blood test?!
Question: I was at the doctor today for a cold that seems to have moved into my chest and is currently causing me to cough up white-yellow phlegm. She gave me a blood test, telling me that by my white blood cell count she could tell if it was viral or bacterial. Unfortunately, she told me it was viral, so I'll have to wait out my illness. But how could she tell? I would think that regardless of whether it is viral or bacterial, that my white blood cells would be elevated to fight it, but she said the count was normal. Why doesn't my white blood cell count go up for a virus but apparently it would for bacteria?
Answers: I was at the doctor today for a cold that seems to have moved into my chest and is currently causing me to cough up white-yellow phlegm. She gave me a blood test, telling me that by my white blood cell count she could tell if it was viral or bacterial. Unfortunately, she told me it was viral, so I'll have to wait out my illness. But how could she tell? I would think that regardless of whether it is viral or bacterial, that my white blood cells would be elevated to fight it, but she said the count was normal. Why doesn't my white blood cell count go up for a virus but apparently it would for bacteria?
You're right - your white blood cell (WBC) count goes up for bacterial as well as viral infections. However, there are several different types of WBCs in a person's bloodstream, including lymphocytes, monocytes, basophils, eosinophils, and neutophils. Immature neutrophils (bands) appear different than mature neutrophils (segmented or "segs") under a microscope lens. During an acute infection, whether of viral or bacterial origin, WBCs will become elevated. Simplest way to explain the next part: your WBCs will usually eradicate a viral infection in 7-10 days with or without medications; you'll have an elevation of total WBCs as well as segs and, possibly, lymphocytes and/or monocytes. Bacterial infections, if left untreated, will progress rapidly. Your body can recognize bacterial -vs- viral infections, as well, and will usually start to "throw everything but the kitchen sink" at it. Stores of WBCs are released, increasing your total WBCs and segs. Frequently, though, your body will "know" it's got a hard battle ahead, so it also releases some of the immature WBC's, the "bands". Bands aren't released during a viral infection. BTW, an increase in bands is also referred to as "Bandemia" or a "left shift". I'm betting your doc saw an increase in total WBCs but no bands, or possibly an elevated WBC count with an increase in lymphocytes and/or monocytes (the WBCs that attack viruses). Something else - although this isn't written into stone - dark yellow-to-green mucus frequently indicates an active bacterial infection, while clear-to-light yellow mucus may frequently indicate a viral infection. Anyway, push the clear fluids, get plenty of rest, and, if you have increasing difficulty breathing or if the mucus begins to get dark (yellow to green), get back to your doc for the antibiotics. Feel better soon!
Viruses are much smaller than bacteria. Too small for your WBCs to detect/fight. WBCs fight larger invaders, like bacteria, some allergens, etc.
So if your white count was normal, the assumption was that your infection was viral.