Blood Test to find infection

Well.. it depends which infection you are looking for.  I would start with a Complete Blood Count, which will give your blood cell counts.  This test will tell you if you have an infection in your body that it is fighting off.  Your White blood cell counts will be really high during an acute infection or it could be really low if it's a chronic infection but.... it will not tell you what kind of infection.  To find out what kind of infection if very hard to do sometimes.  It would have to a test picked by your doctor, based on symptoms.  Say if you have a sore throat, than your doctor will give you a strep test.  If you have more full body symptoms, the an HIV test.  If your having digestive issues, they can do a stool test or breath test to catch some infections.   Also.. for most acute infections, most doctors won't even run blood test to find out the cause.  Most will just give you a round of antibiotics first, and if that don't work, then they will may start to look for a cause.   Sometimes it hard for your family doctor to find a cause if you are very sick, as there are millions of types of bacteria/viruses.. It will all be based on your location and symptoms.  If your doctor cannot find a cause and antibiotics do not work, then you will most likely be referred to a specialist.