Meningitis - Diagnosis

The first clues that a person may have meningitis can be obtained from a simple physical examination. The doctor may try to move the patient's head in various directions. For a person with meningitis, these movements can be difficult and painful.

The standard test for diagnosing meningitis is called a lumbar puncture (LP), or spinal tap. An LP involves the insertion of a thin needle into the space between the vertebrae that make up the spine. A small sample of cerebrospinal fluid is removed. Cerebrospinal fluid (CSF) is a clear liquid present in the space between cells in the brain and the spinal cord. It serves a number of important functions. It provides a cushion for the brain and spinal cord, brings nutrients to these structures, and carries away waste products.

CSF normally contains certain fixed amounts of various chemicals, such as sugar, sodium, potassium, and calcium. An infection in the meninges will cause a change in these amounts. For example, bacteria "eat" sugar, so the presence of bacteria in the meninges causes a reduction in the amount of sugar in the CSF.

The presence of white blood cells in the CSF is also a clue to the presence of meningitis. The immune system produces white blood cells to fight off infections. A healthy body would normally not have white blood cells in the CSF. If they are present, the immune system is probably fighting an infection in the brain or spinal cord, such as meningitis.

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