To diagnose meningitis, a physician will review a medical history and perform a physical examination. One method of diagnosing meningitis is to bend the neck of a patient forward while the person lies flat on his or her back. A person with meningitis will involuntarily flex the knees in response. This is believed to be a reaction to irritation of the inflamed meninges.

Certain medical tests may also be performed that can help determine the nature of the meningitis (e.g., viral or bacterial). If the meningitis is bacterial, these tests can help identify the specific type of bacterium responsible, which can help the physician to devise a more effective treatment plan. It may take a few days before the results of these tests are available. 

These tests include:

• Spinal tap. The insertion of a long needle into the spinal canal to collect cerebrospinal fluid (CSF) for laboratory testing. Analysis of CSF is the only definitive diagnosis method of meningitis. CSF is checked for indicators of an infection (e.g., the number of white blood cells, glucose and protein levels) and then interpreted by a physician to determine if meningitis is present. CSF may also help identify if the source of infection is bacterial or viral. A spinal tap is nearly always performed if meningitis infection is suspected.
  
  
• Throat culture. The back of the throat is swabbed and examined under a microscope. A throat culture can determine if the presence of microorganisms that can cause meningitis or a disease with similar symptoms (e.g., encephalitis) are present. In addition, it may also be helpful in determining the appropriate course of treatment.
  
  
• Imaging tests. Tests that produce images of internal body organs, tissues, structures and pathways (e.g., x-ray, CAT scan, MRI). Imaging tests of certain parts of the body (e.g., chest, skull) may show swelling or inflammation consistent with meningitis and the severity of the infection.
  
  
• Urine tests. Urine may be tested to check for the cause of painful symptoms associated with meningitis.
  
  
• Blood tests. Blood may be analyzed to check counts of white and red blood cells and biochemistry (hormone levels). Cultures of blood can be developed that can be examined for the presence of bacteria or viruses.
  
  
• Polymerase chain reaction (PCR). A DNA test that checks blood for the presence of viruses or parasites. A PCR may be performed if a patient is suspected of having meningitis.
  
  
• Biopsy.  Rarely, a sample of tissue from a rash thought to be caused by meningitis may be removed for laboratory analysis.