If your doctor orders a lumbar puncture test for you, he does so based on your symptoms. Something has led him to believe you have a disease or condition in your brain or spinal column. An examination of the cerebral spinal fluid (CSF) reveals enough information to make a diagnosis and implement a treatment plan.
A continuous membranous sac surrounds your brain and spinal cord. CSF fills the space and acts as a cushion for the central nervous system. The shared CSF flows between the brain and spinal cord. While your other organs have means by which molecules can gain access to them, your brain is designed differently. Instead of having openings or permeable areas for molecular passage, the brain has very tightly fused junctions forming the walls of its blood vessels. This blood-brain barrier insures that only a select few substances can assimilate into your brain.
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Certain molecules can pass easily through the blood-brain barrier, such as oxygen and carbon. Other substances cannot get to the brain via the blood vessels. These include toxins and drugs. Some substances can get through with the help of a transporter such as glucose and amino acids. A lumbar puncture and subsequent study of your CSF reveal if molecules, which ordinarily cannot pass the blood-brain barrier, have gained access. Protein, a large molecule composed of many amino acids, cannot fit through the tight junctions of the brain's circulatory system. When discovered in the CSF, protein signifies certain conditions.
The fact that high levels of protein exist within the CSF infers that some drug or abnormal condition has caused the blood-brain barrier to become more permeable. The normal total value of protein in the CSF ranges from 15 to 45 mg/dL. Fluid color, pressure, the amount and type of white blood cells, and the glucose level give the clinician further clues. The findings, along with your symptoms, narrow down the list of diagnoses. A high protein level in the CSF can represent bacterial or aseptic meningitis, brain tumor, brain abscess, multiple sclerosis, hemorrhage, epilepsy, alcoholism or neurosyphilis, according to the American Academy of Family Physicians.
Making a Diagnosis
The high level of protein in your CSF means a disparity exists. It is not an illness unto itself. Rather, your doctor will have to take many other factors into account before making the diagnosis. If you have a high white blood cell count, she will consider whether you have a bacterial infection or abscess. In the absence of a high white blood cell count, she may order a brain scan to check for a tumor or hemorrhage. Other tests may be needed to rule out MS, epilepsy and syphilis. The elevation of protein represents one aspect of a complicated process that your doctor uses to reach the diagnosis.