The lumbar puncture (or LP) procedure is also referred to as a spinal tap and is a type of diagnostic test. The LP procedure involves collecting a fluid sample from the area surrounding the spinal cord and brain. This fluid, referred to as the CSF or cerebrospinal fluid, circulates within the spinal cord and brain. If you have a lumbar puncture scheduled, then you will probably find it reassuring to learn more about this procedure.

Why Is Lumbar Puncture Procedure Needed?  

A lumbar puncture procedure is frequently done for one of the following reasons:

• Collect cerebrospinal fluid for laboratory analysis
• Inject medications such as chemotherapy drugs into the CSF
• Decrease spinal canal pressure by removing a small quantity of cerebrospinal fluid
• Measure the pressure of spinal canal fluid

A lumbar puncture may also help your doctor diagnose:

• Inflammatory conditions affecting the nervous system, such as multiple sclerosis and Guillain-Barre syndrome
• Cancers of the spinal cord or brain
• Subarachnoid hemorrhage (bleeding near the brain)
• Syphilis, encephalitis, meningitis, and other viral, fungal and bacterial infections

How to Prepare for a Lumbar Puncture Procedure

Prior to your lumbar puncture procedure, you need to let your doctor know if you:

• Take herbal remedies as some may thin your blood
• Might be or are pregnant
• Take blood-thinners like clopidogrel, warfarin, or aspirin or have experienced bleeding problems
• Have any allergies to certain kind of medications
• Are on any medications. And you need to ask your doctor if you should take your medications on the day of your lumbar puncture procedure

Before the procedure begins, you have to empty your bladder and sign a form issuing your consent to it, which states that you understand the risks associated with the procedure and agree to go through with it. You should also talk with your doctor about your concerns, the risks, the results and other related things.

How Is Lumbar Puncture Procedure Done?

Most patients will have a lumbar puncture procedure performed at a hospital or outpatient facility.

• First, you should put on a hospital gown, lie on your side and draw your knees to your chest. Alternatively, you may sit, leaning forward on a stable surface. Each of these positions will flex your back, so the space between your vertebrae widens and your doctor can insert the needle easier.
• Then your doctor washes your back with iodine or antiseptic soap, covers it with a sterile sheet and injects a local anesthetic into the lower back to numb the selected area. This will sting briefly during injection.
• After the anesthetic takes effect, the doctor inserts a hollow, thin needle between the two vertebrae in the lumbar region (the lower area), which travels through your dura (spinal membrane) and enters the spinal canal. At this point, you may notice a sensation of pressure.
• Your doctor may ask you to adjust your position slightly after the needle is placed. They will measure the cerebrospinal fluid pressure, withdraw a small amount of the fluid and measure the pressure again. In some cases, your lumbar puncture procedure will also include the injection of certain substance or drug.
• Finally, the doctor removes the needle and covers the puncture site with a bandage. This procedure will typically take about 45 minutes.

What Is the Normal Result of a Lumbar Puncture Procedure?

The normal values collected during a lumbar puncture will typically be somewhere between the following figures:

• Pressure: 70 to 180mm H20
• Appearance: Clear and colorless
• CSF total protein: 15mg/100 mL to 60mg/100 mL
• CSF glucose: 50mg/100 mL to 80mg/100 mL (or more than ⅔ of the blood sugar level)
• CSF cell count: 0 to 5 white blood cells (which should all be mononuclear) with no red blood cells
• Gamma globulin: 3% to 12% of the CSF total protein
• Chloride: 110mEq/L to 125 mEq/L (milliequivalents per liter)

What Does the Procedure Feel Like?

You may find it uncomfortable to maintain the necessary position for the entire test, but this is necessary as any movement can cause injury to your spinal cord. Sometimes, you are asked to slightly straighten when the needle is placed as this helps measure the cerebrospinal fluid pressure.

You will notice a sensation of hard pressure and brief pain as the needle enters the tissue that surrounds your spinal cord, but the pain will stop within a few seconds. Besides, when the anesthetic is injected, it will burn or sting.

Risk of Lumbar Puncture Procedure

Because an LP procedure involves your brain and spinal cord, there are a number of potential complications that can occur:

• Some CSF may leak from the site where the needle is inserted. This may lead to headaches and severe leakage can cause severe headaches.
• There is a small risk of an infection since the needle breaks the surface of the skin, allowing bacteria to enter through this small hole.
• You may experience temporary numbness or pain in your legs or in the lower back.
• There may be bleeding within the spinal canal.
• If there is swelling or increased pressure in your brain right before the lumbar puncture, it may lead to fluctuating CSF levels, which could cause brain herniation. This is dangerous because your brain swelling may compress the top of your spinal column or your brain stem. This is incredibly rare as doctors always conduct tests before an LP procedure to make sure it is safe.

Depending on your medical history and current conditions, there may be additional risks in your particular situation. You should always discuss risks and concerns with your physician before the procedure.

Follow-Up Care

You should rest following the lumbar puncture procedure and avoid any strenuous activities the same day. If you don’t have a physically active job, you can return to work, but you should always talk to your doctor about the potential activities.

Take pain medication. Many people find nonprescription pain relievers with acetaminophen help reduce back pain or headaches.

If you notice any of the following symptoms after your procedure, contact your doctor immediately:

• Fever or chills
• A stiff neck as this may indicate an infection
• Bleeding or drainage from the site of puncture
• Severe headache
• Loss of strength or numbness below the site of puncture