Lumbar puncture

Produced by Louise Abbott, Bupa Health Information Team, January 2012.

This factsheet is for people who are having a lumbar puncture, or who would like information about it.

A lumbar puncture (sometimes known as a spinal tap) is a procedure used to investigate the cerebrospinal fluid, which surrounds the brain and spinal cord. It’s used to help diagnose conditions affecting the brain and the spinal cord.

You will meet the doctor carrying out your procedure to discuss your care. It may differ from what is described here as it will be designed to meet your individual needs.

About a lumbar puncture

In a lumbar puncture, your doctor takes a sample of cerebrospinal fluid from within your spinal canal in your lower back using a very fine needle.

Your doctor can use the fluid collected by a lumbar puncture to help diagnose certain conditions that can affect your brain, spinal cord and nervous system. Some of these conditions include:

• meningitis – this is inflammation of the lining of your brain
• encephalitis – this is inflammation of your brain
• myelitis – this is inflammation of your spinal cord
• subarachnoid hemorrhage – this is bleeding around your brain
• nervous system diseases, such as multiple sclerosis
• cancer affecting the membranes around your brain or spinal cord

You may sometimes have a lumbar puncture done so that medicine can be given directly into the cerebrospinal fluid. Medicines such as antibiotics or cancer treatments can be given in this way.

Preparing for a lumbar puncture

This procedure is often carried out if you have been admitted to hospital in an emergency, for example, if your doctor suspects you may have meningitis. Alternatively, you may have this procedure in hospital as a pre-arranged day case, which means you will be able to go home on the same day.

A doctor will ask you about your medical history. For example, he or she will check that you aren’t taking any blood-thinning medicines that would make having a lumbar puncture more of a risk for you. If a problem is found with your blood clotting, it’s likely that you won’t be able to have a lumbar puncture carried out. Speak to you doctor to find out about alternative procedures.

Before the lumbar puncture, you will usually be asked to change into a gown. If you’re feeling very anxious, your doctor may give you a sedative to take before the procedure. This relieves anxiety and helps you to relax.

A lumbar puncture is carried out under local anaesthesia. This completely blocks pain from the area of your back where the needle is inserted and you will stay awake during the procedure.

Your doctor will discuss with you what will happen before, during and after your procedure, and any pain you might have. This is your opportunity to understand what will happen, and you can help yourself by preparing questions to ask about the risks, benefits and any alternatives to the procedure. This will help you to be informed, so you can give your consent for the procedure to go ahead, which you may be asked to do by signing a consent form.

If you’re having a lumbar puncture in an emergency situation, it may not be possible to ask you to sign a consent form.

What happens during a lumbar puncture

A lumbar puncture usually takes about half an hour, although the needle is in place for only about one minute. You will probably be asked to lie on a bed on your left side with your knees pulled up towards your chest and your chin tucked in. You will need to make your back as rounded as you can towards your doctor, who will sit behind you. This position makes it easier for your doctor to find the right place on your spine to carry out the procedure. If you find this position awkward, you may be asked to lean forward over the back of a chair or table instead.

Your doctor will clean the area of your back where the needle will enter. He or she will use an antiseptic solution, which may feel cold. Next, your doctor will inject the area with local anaesthetic. After the anaesthetic has taken effect, he or she will insert a long, fine needle into the space between two bones (vertebrae) in your lower spine. As you will have had local anaesthetic, this won’t be painful, but you may feel uncomfortable or have strange, tingling sensations in your legs. You may feel a ‘pop’ as the needle goes through the tough layer around the cerebrospinal fluid. However, it’s important you remain still.

Your doctor may measure the pressure of your cerebrospinal fluid by connecting a device called a manometer to the needle. He or she may ask you to straighten your legs while the pressure is measured. Your doctor will then collect three or four samples of cerebrospinal fluid in small tubes. These will be sent to the laboratory for analysis.

After the fluid has been collected, your doctor will remove the needle. He or she will then clean the area of your back again and cover the small scratch with a plaster or sterile dressing.

What to expect afterwards

You may get a headache after having a lumbar puncture. It’s still unclear why this happens but it’s likely to be caused by cerebrospinal fluid continuing to leak into the surrounding tissue from the hole that has been made through the tissues that hold the cerebrospinal fluid. Your doctor will probably ask you to get up soon after the lumbar puncture, as long as you feel well enough.

Your back may feel a little sore where the needle was put in, but this won’t last more than a couple of days.

You will be able to go home when you feel ready, but you will need to arrange for someone to drive you. 

What are the risks?

As with every procedure, there are some risks associated with a lumbar puncture. We have not included the chance of these happening as they are specific to you and differ for every person. Ask your doctor to explain how these risks apply to you.

Side-effects

Side-effects are the unwanted but mostly temporary effects you may get after having the procedure. You may have some pain in your lower back where the needle was put in. This should go away after a couple of days.

Complications

Complications are when problems occur during or after the procedure. Most people aren’t affected. Possible lumbar puncture-related complications include those listed below.

• You may get a severe headache after the lumbar puncture. This happens in up to four in 10 people who have this procedure. It’s important that you drink enough fluids as this may help to reduce the headache. You can take over-the-counter painkillers, such as paracetamol or ibuprofen for this and you may find that lying down helps to relieve the pain. Always read the patient information leaflet that comes with your medicine and if you have any questions, ask your pharmacist for advice.
• If you have a very severe headache that doesn’t seem to be getting any better, you may need to have another procedure to help stop the pain. This involves injecting a small amount of your own blood into the space where the needle was put in. This helps to plug the hole that the cerebrospinal fluid is leaking from and stops the headache.
• Your doctor may not be able to collect any cerebrospinal fluid. This could happen if you are dehydrated, so you may need to have another lumbar puncture after you have been given something to drink to make sure you’re hydrated enough.
• You could get an infection in or around where the needle was inserted. This is rare because your lumbar puncture will be carried out in a sterile way. However, you may need to be treated in hospital with antibiotics or surgery if this happens.
• You may get excessive bleeding from where the needle was inserted. This is rare and isn’t usually serious unless you already have a problem with your blood clotting.
• You may have strange, tingling sensations in your legs if the needle has touched a nerve during the procedure. This usually gets better without any treatment.
• You may get cerebral herniation. This is a very rare complication that causes high pressure within the brain. Your doctor will carry out tests to check whether you’re at risk of this problem and may arrange for you to have a MRI or CT scan before the lumbar puncture to make sure the procedure is safe for you. If these scans show there is a problem, you may not be able to have the lumbar puncture carried out.

For answers to frequently asked questions on this topic, see Common questions.

For sources and links to further information, see Resources.