How Is Meningitis Diagnosed?

If meningitis is suspected, treatment should be sought immediately.

At the hospital, a doctor can make a quick diagnosis by withdrawing a small sample of the spinal fluid for examination. This procedure is called a lumbar puncture (spinal tap). It involves inserting a needle into the middle of the lower back and collecting some drops of fluid. The procedure can be slightly uncomfortable but is rarely painful with the use of a local anesthetic.

Laboratory analysis of the spinal fluid will confirm if the meninges are infected. The tests can usually, but not always, determine what type of germ has infected the patient.

• In mild forms of meningitis the lumbar puncture may alleviate a patient's headache, possibly by reducing the fluid's pressure on the meninges.

At the hospital, blood tests are also taken to look for the germ in the blood and to check that the patient is otherwise healthy.

In newborns, doctors may also check the fluid in their stomach with a small tube passed down the throat, and test their feces for the presence of suspected germs.

Diagnosis cannot be made through imaging tests, such as X rays or ultrasound. However, these tests can be used to insure that the brain is not in damage from pressure or the accumulation of fluid. Doctors may also order a chest X-ray, since as many as half of patients with pneumococcal meningitis also have evidence of pneumonia.