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Lumbar puncture

A lumbar puncture is a medical procedure where a sample of fluid is taken from inside the lower back for testing.

A hollow needle is inserted between two bones, called vertebrae, at the base of the spine and is used to draw fluid out.

A lumbar puncture is most commonly carried out when it's thought that a condition such as meningitis has developed inside the brain or nervous system. Meningitis is a serious infection of the membranes that surround the brain and spinal cord.

Cerebrospinal fluid

Cerebrospinal fluid (CSF) is a colourless fluid that surrounds and supports the brain and spinal cord. In the same way that studying a blood sample can tell doctors about the health of a person’s body, studying a sample of CSF can often reveal a great deal about the health of a person’s brain and nervous system.

For example, if bacteria are found in a sample of CSF, it's highly likely to be the result of a brain infection. If a large number of red blood cells are found in a sample of CSF, it may be due to bleeding inside the brain.

When a lumbar puncture is used

The most common reason for a lumbar puncture being carried out is to diagnose a suspected case of:

• meningitis 
• bleeding on the brain (subarachnoid haemorrhage)
• Guillain-Barré syndrome – a condition that causes inflammation of the nervous system

How a lumbar puncture is done

During a lumbar puncture, a hollow needle is inserted in between the two bones at the base of your spine and into the space surrounding the spinal cord. A small sample of a few millilitres of CSF is removed for testing.

A lumbar puncture takes around 45 minutes and is carried out under local anaesthetic, so you should not feel any pain.

If your child needs to have a lumbar puncture, they will be given medication to help relax them and keep them calm.

Read more about how a lumbar puncture is performed.

Safety

A lumbar puncture is generally safe and the risk of developing serious side effects from a lumbar puncture is relatively low.

A headache is the most common side effect and occurs in about one-third of cases. It can develop 24–48 hours after the procedure and can be moderate or severe.

Reducing risk

A study conducted in France found that about 14% of lumbar punctures detected a serious condition.

As conditions such as meningitis can be life threatening if they're not quickly diagnosed and treated, it's considered better to carry out a lumbar puncture than to take any chances.

Being told that you or your child need a lumbar puncture may cause you a lot of worry, but it doesn't necessarily mean that you have a serious condition.

Why it is necessary

A lumbar puncture is most commonly carried out to help diagnose three conditions:

• meningitis
• subarachnoid haemorrhage
• Guillain-Barré syndrome

Meningitis

The most common reason for a lumbar puncture is to help confirm or rule out a diagnosis of meningitis.

Meningitis is an infection of the outer layers of the brain and spinal cord. These layers are known as the meninges. The infection can be:

• viral – which can cause unpleasant flu-like symptoms but is not particularly serious
• bacterial – which is a medical emergency and, if not treated, can lead to coma, brain damage or death

Children under five years of age are most vulnerable to developing bacterial meningitis, which needs immediate treatment. The symptoms of meningitis can include:

• drowsiness
• confusion
• sometimes a blotchy red rash that does not fade when a glass is placed against it

A lumbar puncture can be used to check for the presence of bacteria or viruses in the cerebrospinal fluid (CSF).

Levels of white blood cells and sugar are also measured. A high white blood cell count and a low sugar count are often signs of infection.

Subarachnoid haemorrhage

A subarachnoid haemorrhage is an uncommon cause of a stroke, where blood leaks out of blood vessels over the surface of the brain.

As with all strokes, a subarachnoid haemorrhage is a medical emergency. It requires immediate treatment to prevent serious complications, such as brain damage and death.

The most common symptom of a subarachnoid haemorrhage is a sudden and severe headache, which feels like suddenly being hit on the head and is often unlike anything ever experienced before.

A lumbar puncture can be used to determine whether there is any blood in the CSF, which is often a sign of bleeding inside or around the brain.

Guillain-Barré syndrome

Guillain-Barré syndrome is a rare condition that affects around 1,500 people in the UK every year. It causes inflammation of the nervous system which disrupts its normal working.

The symptoms of Guillain-Barré syndrome, such as tingling in the hands and feet, start gradually and steadily get worse. Someone with the condition may eventually be unable to walk or swallow food.

A lumbar puncture can be used to check the protein level in the CSF. In Guillain-Barré syndrome, the amount of protein is usually higher than normal.

A lumbar puncture is also useful for ruling out other possible causes of the symptoms, such as a subarachnoid haemorrhage.

Providing treatment

As well as being used to diagnose conditions, a lumbar puncture is sometimes used to give treatments, including antibiotics or chemotherapy medicine for cancer.

A lumbar puncture can also be used to remove CSF to relieve pressure placed on the skull by the brain and fluid inside the skull cavity (known as high intracranial pressure). For example, this might be used in a condition called idiopathic intracranial hypertension, which mainly affects overweight women of childbearing age.

A lumbar puncture is an effective way of providing short-term symptom relief until a more permanent method of treatment can be provided.

How it is performed

Preparation

Sometimes, a computerised tomography (CT) scan of your brain may be carried out before a lumbar puncture to check that there's nothing wrong with the pressure inside the skull. If there is something wrong, it may be too dangerous to do a lumbar puncture because it could damage the brain.

A neurologist, who specialises in treating conditions of the brain and nervous system, or a doctor with expertise in emergency medicine will usually carry out the lumbar puncture.

They will explain why the procedure is required and any possible risks. You will then be asked to provide your consent to have the procedure.

If it is not possible for you to provide informed consent - for example, if you are unconsciousness or mentally confused - a lumbar puncture may be carried out if it's considered too dangerous to wait until you can give consent.

The procedure

You may be asked to lie on one side with your legs pulled up and your chin tucked in, so that your spine is curved. This will help separate the bones in your spine, allowing the needle to be inserted more easily. Sitting while bending forwards also works well.

An antiseptic solution will be applied to the skin at the base of your spine, which may feel cold. A local anaesthetic will then be used to numb the area of skin around your lower back.

If your child is having a lumbar puncture, they may be given medication to help keep them calm (a sedative) or be held in position. This is because it's very important to keep still during the procedure.

The doctor will push a hollow needle in between the two bones at the base of the spine and into the space around the spinal cord. The anaesthetic should help prevent you feeling any pain, although there may be some pressure as the needle is pushed in. Some people feel a sharp sensation in their back or leg.

After the needle has been inserted, a small amount of cerebrospinal fluid (CSF) will drip back into a sterile pot underneath the needle. Only a few millilitres of CSF are usually removed.

If the doctor needs to measure the pressure of the CSF, they will attach a special tube to the needle to check the pressure of the fluid coming out. Once the procedure is complete, the needle will be removed and a small plaster will be put on the skin.

The CSF sample will be sent to a laboratory to be tested. The lumbar puncture procedure usually takes about 45 minutes.

After the procedure

After having a lumbar puncture, you will be asked to lie flat on your back for a few hours. This can sometimes help prevent a headache developing.

How soon you can return home depends on why the lumbar puncture was carried out. If it's thought there may be a threat to your health, such as meningitis, you will probably need to stay in hospital as a precaution until the results of the tests are known.

However, if your condition is not thought to be serious, you will probably be able to leave hospital on the same day.

You can remove the plaster after 24 hours and you should drink plenty of fluids over the next few days. Do not drive for 24 hours after having a lumbar puncture.

If your child has had the procedure and the results show that nothing is seriously wrong, they will be able to go to school the following day. However, they should avoid playing sports or doing PE for a week.

Side effects

Headaches

A headache is a common side effect of a lumbar puncture. One-third of people will develop a headache, usually within 24–48 hours of having the procedure. However, in some cases, it can take up to 12 days for the headache to develop.

Pregnant women and young, slim women who are 18–30 years of age are thought to be most at risk of developing a headache after having a lumbar puncture.

The cause of the headache is unclear. One theory is that a temporary disruption in the fluid surrounding the brain causes the brain to sag, placing pressure on pain-sensitive areas of the brain.

Most people describe having a dull or throbbing pain at the front of their head that can sometimes spread to their neck and shoulders. The pain is usually worse when standing or sitting up and moving your head. Lying down often helps relieve the pain.

In most cases, the pain is mild and can be treated with painkillers, such as paracetamol, which are available from pharmacies. Some people have also reported that drinks containing caffeine, such as coffee, tea and or cola, have helped reduce their symptoms of pain.

Severe headaches

A small number of people have more severe pain after a lumbar puncture. Contact your GP for advice if you develop a severe headache. You may need to be admitted to hospital so that you can be given stronger pain relief.

If you cannot speak to your GP, call NHS Direct on 0845 4647 or contact your local out-of-hours service.

Treatments for severe headaches include using stronger, opiate-based painkillers or injecting painkilling medication directly into the skull.

When to get medical advice

Contact your GP for advice if you or your child have any of the following symptoms after having a lumbar puncture:

• vomiting or nausea
• high temperature (fever) of 38C (100.4F) or above swelling and redness around the injection site
• clear fluid or blood leaking from the injection site
• sensitivity to bright lights

Results

Some tests involving cerebrospinal fluid (CSF), such as a white blood cell count or checking for red blood cells, can be done quite quickly.

In the case of a medical emergency, the test results should be available within a couple of hours.

Other tests, such as checking for bacteria, are more complex and may take 48 hours to complete.

In non-emergency cases, such as having a lumbar puncture to help confirm or rule out a diagnosis of Guillain-Barré syndrome, it may take several weeks for the results to become available.