Lumbar punctures are carried out in hospital. This may be after an emergency admission, or the procedure may be arranged in advance.

Preparation

Before a lumbar puncture, checks will be made to confirm the procedure is safe for you. Usually a computerised tomography (CT) scan or an magnetic resonance imaging (MRI) scan will have been carried out to make sure the lumbar puncture is needed and will not cause any harm. It will not be done if you have recently taken blood-thinning medication (anticoagulants) such as warfarin.

A doctor or nurse will explain why it’s needed and you’ll be asked to provide written consent for it. 

If it’s not possible for you to provide informed consent – for example, if you are unconscious or confused, the medical staff may decide to go ahead with the procedure, if it’s in your best interests. This will normally be discussed with close relatives, but the final decision is made by medical staff.

You will usually change into a hospital gown before the procedure. As the lumbar puncture can take some time, you might want to use the toilet beforehand.

The procedure

In most cases, you’ll be asked to lie on one side and to curl up, with your knees up and your chin in, so your spine is curved. This helps to separate the bones in your spine, allowing the needle to be inserted more easily.

Sitting while bending forwards is an alternative position, although it’s not always suitable.

An antiseptic solution will be applied to the skin at the base of the spine. A local anaesthetic is then used to numb the area of the lumbar puncture site. If a child needs to have a lumbar puncture, medication may be given beforehand to help them relax and keep calm.

The doctor (or sometimes a specially trained nurse) will insert a special spinal needle between the bones at the base of the spine and into the spinal canal, penetrating the membrane containing the cerebrospinal fluid (CSF).

Occasionally, you may feel a sudden, sharp sensation in one of your legs if the needle tip touches one of the nerves within the spinal canal. This is only a brief pain and it will indicate to the doctor a need to adjust the needle’s direction.

Once the needle is in the correct position, the CSF will begin to drip out. Usually, the CSF pressure is then measured by attaching a length of plastic piping to the needle to see how far up the tube the fluid rises. This is called manometry. You may be asked to cough or strain while this is being done and the doctor may press gently on one side of your neck, to check that the CSF can pass freely between your head and spinal canal.

Following manometry, samples are usually collected in sterile containers. Only a small amount is normally needed for testing, but more may be removed if the doctor needs to reduce the pressure within the head.

Once the procedure is complete, the needle will be removed and a small plaster is applied. The whole procedure usually takes about 30-45 minutes, in most cases.

It normally takes your body less than two days to replace the fluid naturally.

After the procedure

Afterwards, you may be asked to lie flat for a period of time to reduce the chances of a post-lumbar puncture headache developing, although most headaches don’t develop for at least several hours and often not until the next day. You will normally have your pulse and blood pressure checked again.

Most people undergoing non-emergency lumbar puncture on a day-case basis will be allowed to return home as soon as possible, where they can be more comfortable and can treat any headaches with bed rest, drinking plenty of fluids and taking simple painkillers. The plaster can be removed the following day.

Returning to normal activities depends on how severe any post-lumbar puncture headache is and how long it lasts, but you should avoid driving or operating machinery for 24 hours. Once you can get up and about without experiencing troublesome headaches, you can return to normal activities, including work or school and driving. However, it’s best to avoid sports and strenuous activities for at least a week.

Getting the results

Your doctor or nurse who performs the lumbar puncture can tell you the results of pressure measurements straight away, and explain what they mean. The results of some laboratory tests, such as looking for signs of inflammation or checking for evidence of bleeding into the head, are available quite quickly – within a couple of hours, in an emergency.

Other tests, such as identifying bacteria causing meningitis, are more complex and may take at least 48 hours to complete. More specialised tests may take several days.