Lumbar puncture (spinal tap) is the most common means of collecting a specimen of CSF. You are positioned on your side with your knees curled up to your abdomen and your chin tucked in to your chest. (Occasionally this procedure is performed with the person sitting bent forward).

The skin is scrubbed, and a local anesthetic is injected over the lower spine. The spinal needle is inserted, usually between the 3rd and 4th lumbar vertebrae.

Once the needle is properly positioned in the subarachnoid space, pressures can be measured and fluid can be collected for testing. After the sample is collected, the needle is removed, the area is cleaned, and a bandage is applied. You will be asked to remain flat, or nearly flat, for 6 to 8 hours after the test.

Lumbar puncture (with fluid collection) may also be part of other procedures, particularly a myelogram (X-ray or CT scan after dye has been inserted into the CSF).

Alternative methods of obtaining CSF are rarely used, but may be indicated if there is a problem such as lumbar deformity or infection, which would make lumbar puncture impossible or unreliable.

Cisternal puncture involves insertion of a needle below the occipital bone (back of the skull). It can be hazardous because the needle is inserted close to the brain stem.

Ventricular puncture is even more rare, but may be indicated when sampling of CSF is necessary in people with possible impending brain herniation. It is usually performed in the operating room. A hole is drilled in the skull and a needle is inserted directly into the lateral ventricle of the brain.

• Infant test or procedure preparation (birth to 1 year)
• Toddler test or procedure preparation (1 to 3 years)
• Preschooler test or procedure preparation (3 to 6 years)
• Schoolage test or procedure preparation (6 to 12 years)
• Adolescent test or procedure preparation (12 to 18 years)

The position may be uncomfortable, but it is imperative that you remain in the curled position to avoid moving the needle and possibly injuring the spinal cord.

The scrub will feel cold and wet. The anesthetic will sting or burn when first injected. There will be a hard pressure sensation when the needle is inserted, and there is usually some brief pain when the needle goes through the meninges. This pain should stop in a few seconds.

Overall, discomfort is minimal to moderate. The entire procedure usually takes about 30 minutes, but it may take longer. The actual pressure measurements and fluid collection only takes a few minutes.

• Pressure: 50 to 180 mm H20
• Appearance: clear, colorless
• CSF total protein: 15 to 45 mg/100 ml
• Gamma globulin: 3 to 12% of the total protein
• CSF glucose: 50 to 80 mg/100 ml (or approximately 2/3 of serum glucose level)
• CSF cell count: 0 to 5 white blood cells (WBC), no red blood cells (RBC)
• chloride: 110 to 125 mEq per liter

Note: mg/ml = milligrams per milliliter; mEq/L = milliequivalent per liter

(See also CSF coccidioides complement fixation, CSF culture, CSF oligoclonal banding, CSF smear, CSF VDRL test.)

• Pressure, increased: increased intracranial pressure (pressure within the skull) from trauma or infection
• Pressure, decreased: obstruction to the flow of CSF above the puncture site (spinal cord tumor), shock, fainting, diabetic coma
• Appearance
  • Cloudy: infection, white blood cells in the CSF, protein in the CSF, microorganisms
  • Bloody or reddish colored: bleeding within the brain or subarachnoid space, spinal cord obstruction, traumatic lumbar puncture (first specimen bloody, rest clear)
  • Brown, orange, yellow color: elevated protein in the CSF, old (greater than 3 days) blood in the CSF
• Protein, increased: blood in the CSF, diabetes, polyneuritis, tumors, trauma, any inflammatory or infectious condition
• Protein, decreased: rapid CSF production
• Gamma globulin, increased: demyelinating disease (e.g. multiple sclerosis), neurosyphilis, Guillain-Barre syndrome
• Glucose, increased: systemic hyperglycemia (elevated blood sugar)
• Glucose, decreased: systemic hypoglycemia (low blood sugar), bacterial or fungal infection (such as meningitis), tuberculosis, carcinomatous meningitis
• WBC, increased: active meningitis, acute infection, beginning of a chronic illness, tumor, abscess, brain infarction (stroke), demyelinating disease (such as multiple sclerosis)
• RBC: bleeding into the spinal fluid, traumatic lumbar puncture

Additional conditions under which the test may be performed:

• Chronic inflammatory polyneuropathy
• Dementia due to metabolic causes
• Encephalitis
• Epilepsy
• Febrile seizure (children)
• Generalized tonic-clonic seizure
• Hydrocephalus
• Inhalation anthrax
• Normal pressure hydrocephalus (NPH)
• Pituitary tumor
• Reye's syndrome

• Risks of lumbar puncture include:
  • Hypersensitivity (allergic) reaction to the anesthetic.
  • Discomfort during the test.
  • Headache after the test.
  • Bleeding into the spinal canal.
• Brain herniation (if performed on a person with increased intracranial pressure), and resulting in brain damage or death.
• Damage to the spinal cord (particularly if the person moves during the test).
• Cisternal puncture or ventricular puncture carry additional risk of damage to the brainstem or brain tissue and risk of bleeding within the brain; resulting in incapacitation or death.