You or your child may undergo the following diagnostic tests:

• Blood cultures. Blood samples are placed in a special dish to see if it grows microorganisms, particularly bacteria. A sample may also be placed on a slide and stained (Gram's stain), then studied under a microscope for bacteria.
• Imaging. Computerized tomography (CT) or magnetic resonance imaging (MRI) scans of the head may show swelling or inflammation. X-rays or CT scans of the chest or sinuses also may show infection in other areas that may be associated with meningitis.

• Spinal tap (lumbar puncture). For a definitive diagnosis of meningitis, you'll need a spinal tap to collect cerebrospinal fluid (CSF). In people with meningitis, the CSF often shows a low sugar (glucose) level along with an increased white blood cell count and increased protein.

  CSF analysis may also help your doctor identify which bacterium caused the meningitis. If your doctor suspects viral meningitis, he or she may order a DNA-based test known as a polymerase chain reaction (PCR) amplification or a test to check for antibodies against certain viruses to determine the specific cause and determine proper treatment.