Viral meningitis is usually diagnosed by laboratory tests of spinal fluid obtained with a spinal tap. The specific cause of viral meningitis can be determined by tests that identify the virus in specimens collected from the patient, but these tests are rarely done.
Diagnosis is based upon clinical history compatible with meningitis, and a physical exam in which pain is elicited upon flexing the neck. Often a patient with meningitis will have so much pain that the neck will be rigid.
A spinal tap (collecting spinal fluid by means of a small needle inserted into the back) will often demonstrate cells under the microscope compatible with a viral infection.
All types of meningitis are diagnosed by growing bacteria from a sample of the infected person's spinal fluid, which is collected by performing a lumbar puncture (spinal tap). Results show whether or not the cerebral spinal fluid (CSF) has increased white blood cells. Blood tests are also conducted to determine whether or not there is a significant increase or decrease in the white blood cell count.
Because viral meningitis has symptoms in common with bacterial meningitis, which is life-threatening, it's important to get an immediate diagnosis. Your doctor will evaluate your or your child's symptoms, looking for specific signs such as the combination of fever, headache, and stiff neck. To confirm the diagnosis, your doctor will need to do a lumbar puncture, also known as a spinal tap, to withdraw some cerebrospinal fluid (CSF) and check for a viral infection. Before the fluid is withdrawn, an area in the lower back is numbed with a local anesthetic. Then, a long, hollow needle is inserted into the spinal canal to withdraw the fluid. If the symptoms are caused by a virus, the fluid will have a high number of white blood cells. The fluid will also be examined under a microscope and sent to a laboratory where it will be grown (cultured) in case a bacteria is present.
Your doctor will ask questions about your health, do an exam, and use one or more tests.
Lumbar puncture is the most important lab test for meningitis. It is also called a spinal tap. A sample of fluid is removed from the spine and tested to see if it contains organisms that cause the illness.
Your doctor may also order other tests, such as blood tests, a CT scan, or an MRI.
