Cerebrospinal Fluid Testing

Cerebrospinal fluid testing is a set of laboratory analyses that contains samples of the fluid surrounding the brain and spinal cord area. Cerebral spinal fluid (CSF) is a clear watery fluid that occupies the space between the subarachnoid cavities and the pia mater. CSF acts as a cushion for the cortex while protecting the brain. It also provides nutrients to the central nervous system and helps regulate its waste products by flowing them back to the blood stream. The fluid that flows inside and around the brain and the spinal cord contains amino acids, electrolytes, glucose, and other molecules found in the plasma.

How the Test is Performed

There are many ways to get samples of the spinal fluid, they are:

• Lumbar Puncture

Lumbar puncture (LP) or also commonly known as spinal tap is performed by letting the patient lay down at his/her side in a fetal position (knees pulled up and chin tucked down). After cleaning the back area, a health care provider will first inject the anesthesia right into the lower spine. Once the anesthesia takes effect, a spinal needle will be inserted to the patient’s lower back area. The needle should be well positioned before collecting any spinal fluid. Once positioned, the spinal fluid pressure will first be measured then the fluid can now be collected. When done, the needle will be taken out and the needle site will be cleaned and bandaged.

Occasionally, a special x-ray called fluoroscopy will be used to help guide the needle into its proper position.

• Cisternal Puncture

CSF collection through cisternal puncture is rarely used. A needle is positioned below the occipital bone. This procedure can be dangerous because occipital bone lies close to the brain stem. This procedure is usually done for patients with back deformity or signs of infection are present.

• Ventricular Puncture

Ventricular puncture are recommended for patients with brain herniation and this procedure is done in an operating room. A hole is drilled directly into the skull exposing the brain’s ventricles, and then a needle will be inserted into the ventricles to collect the CSF sample.

Why Cerebrospinal Fluid Test is Performed

Cerebrospinal fluid testing is performed to check the pressure within. Collecting samples of fluid is done for further fluid testing. CSF analysis is used to diagnose certain medical conditions that might affect the central nervous system, like:

• Meningitis and Encephalitis

• Metastatic tumors and other tumors that shed tumor cells into the cerebral spinal fluid

• Syphilis

• Brain and spinal cord bleeding

• Multiple sclerosis

• Guillian-Barré syndrome

Precautions and Risks while Performing Cerebrospinal Fluid Testing

Performing lumbar puncture should be done with extreme caution. Some of the mild risks associated with lumbar puncture are:

• Hypersensitivity reaction to the anesthesia

• Discomfort during the procedure

• Headache after the procedure

Patients with bleeding disorders during a cerebrospinal fluid testing can suffer hemorrhage. The hemorrhage can cause increase in pressure at the spinal column which may lead into brain tumor and other serious conditions. Once the CSF is removed from a high pressure it causes brain herniation. Brain herniation causes the brain stem to compress, resulting to irreversible brain damage or even death.

Damaging the nerves might be at risk especially when the patient moves while performing the cerebrospinal fluid testing.

There is risk of introducing harmful bacteria into the blood stream while performing cerebrospinal fluid testing which causes meningitis.

If analysis of the sample fluid taken will not be performed immediately, keep the specimens refrigerated to avoid contamination.

Cerebrospinal Fluid Testing: Normal and Abnormal Results

Normal results should be as follows:

• CSF Opening Pressure: 50–180 mm H2O

• Appearance: Clear and colorless

• CSF total Protein: 15 to 60mg/100 mL

• Gamma Globulin: 3–12% from CSF total protein level

• CSF Glucose: 50 – 80 mg/100 mL

• LD: 1/10 of serum level

• Lactate: less than 35 mg/100 mL

• Leukocytes or white blood cells: for adults and children 0-5/microL while on infants up to 30/microL

• Chloride: 110–125 mEq/L

Abnormalities in the CSF

• Blood

Accidental puncture of the leptomeningeal vein during an entry of the lumbar puncture (LP) can cause spillage of blood into the CSF. Such blood stains will be initially drawn out from the blood stream but if not, the blood indicates a subarachnoid hemorrhage. In 3 to 7 days the erythrocytes from the subarachnoid hemorrhage will eventually clear out.

• Increased Inflammatory Cells

Increased inflammatory cells or pleocytosis are caused by both infectious and non-infectious processes. Polymorphonuclear pleocytosis indicates presence of acute suppurative meningitis.

• Tumor Cells

Presence of tumor cells indicates spreading of brain tumors in the subarachnoid space. It is best detected with a cytological examination.

• Increased Protein

Normal protein level of CSF is 15 to 60mg/dL but in some condition like bacterial meningitis infection, protein level would rise up to 500mg/dL. High level of protein may indicate signs of bleeding, tumor, injury, or nerve inflammation.

• Low Glucose

Abnormal level of glucose in the CSF usually reflects the blood sugar level. Some conditions that may cause glucose to be low are bacterial meningitis, mumps meningitis, subarachnoid hemorrhage, tuberculosis meningitis, fungal meningitis, and other cause of meningitis.

If the cerebrospinal fluid looks cloudy, a possible infection or build up of white blood cells or protein is most likely happening. If CSF looks bloody, then possible bleeding might be occurring. When the color is orange, brown, or yellow possible increase of protein level might be present or a previous bleeding just occurred more than 3 days prior to cerebrospinal fluid testing.