Why Is Protein Elevated in Bacterial Meningitis?

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Bacterial meningitis is a potentially serious infection of the meninges, the tissue covering of the brain and the spinal cord. Viruses, bacteria and fungi can cause meningitis, and one of the ways to tell which microorganism is causing the infection is by measuring the level of protein in the spinal fluid. Bacterial meningitis typically causes high levels of protein in the spinal fluid.

Spinal Fluid

The spinal fluid is a clear liquid that bathes the brain and the spinal cord. According to MedlinePlus, the spinal fluid acts as a cushion to protect the brain and the spinal cord against shocks. It also plays an important role in the metabolism of the brain. Normally, the spinal fluid contains between 15 and 45mg/dl of protein. When a person suffers from bacterial meningitis, the level of protein in the spinal fluid can rise markedly, up to 500mg/dl.

Protein in Spinal Fluid

According to an article in the journal "American Family Physician," the level of protein in the spinal fluid is one of the most sensitive indicators of disease in the central nervous system. The main protein in spinal fluid is albumin, a large protein important in the body’s fluid balance. During bacterial infection, the level of protein in the spinal fluid goes up, due to an increase in the presence of the replicating bacteria, which have a high composition of protein, and an increase in the number of cells that fight infection and inflammation, which are also composed of protein.

Obtaining Spinal Fluid

The method to obtain spinal fluid to measure its protein content is called a lumbar puncture, or spinal tap. After anesthetizing the skin with lidocaine, a physician inserts a needle in the lower back, in between the vertebra in the region, while the patient lies on his side, or sits up bending forward. The physician advances the needle into the intervertebral space, obtaining the fluid sample. Spinal fluid is usually as clear as water, but in cases of bacterial meningitis it can appear cloudy.

Symptoms of Bacterial Meningitis

The symptoms of bacterial meningitis include headache, fever, photophobia or aversion to bright lights, nausea and vomiting. Some bacteria that cause meningitis can produce bruising or rashes in the skin. Neck stiffness is also a common symptom. Bacterial meningitis is a potentially fatal condition, so prompt diagnosis, including determination of protein level in the spinal fluid, is important to prevent long-term complications or death.