A lumbar puncture, sometimes called a spinal tap, uses a thin needle in your lower back to collect a small sample of cerebrospinal fluid (CSF). This is the clear fluid around your brain and spinal cord. In neurology it helps diagnose meningitis, multiple sclerosis (MS) and bleeding around the brain. It also helps with raised brain pressure and some dementias.
The procedure usually takes 15 to 20 minutes under local anaesthetic. The most common side effect is a headache. In trials, it affected about 1 in 9 people with standard needles and about 1 in 24 with "atraumatic" needles. Serious complications are rare. Results can come back in days or take a few weeks, depending on the tests.
Brain scans show structure. CSF shows what is happening chemically and immunologically around the brain. That is why a lumbar puncture can answer questions a scan cannot.
When bacterial meningitis is suspected, NICE recommends a lumbar puncture before antibiotics, if it is safe and will not delay treatment (NICE NG240). If antibiotics have already started, it should be done as soon as safely possible.
Doctors also measure blood sugar just before the procedure. This lets them compare CSF glucose with blood glucose.
A sudden, severe "thunderclap" headache can be a sign of bleeding into the space around the brain. NICE says the first test is an urgent CT scan (NICE NG228). If a CT done within six hours of the headache starting is normal, NICE advises against routinely doing a lumbar puncture. If the CT was done after six hours and is normal, a lumbar puncture should be considered.
Timing matters. NICE says to wait at least 12 hours after the headache started. The lab then looks for xanthochromia, a yellow colour from broken-down blood, using a technique called spectrophotometry.
In MS, the immune system makes antibodies inside the central nervous system. These show up in the lab as oligoclonal bands (OCBs). When bands are found in the CSF but not in the blood, they point to antibody production within the brain and spinal cord.
Since 2017, the McDonald criteria let CSF-specific bands stand in for some of the MRI evidence otherwise needed (Thompson et al., Lancet Neurol 2018). The 2024 revision added another CSF test, kappa free light chains. A review of the new criteria describes this as interchangeable with OCBs for showing a positive CSF result (Samara and Ontaneda, Biomedicines 2025). NICE now tells doctors to follow the 2024 criteria (NICE NG220).
OCBs are common in MS but not universal. A meta-analysis found them in 87.7% of 12,253 people with MS (Dobson et al., JNNP 2013). They were found in 68.6% of 2,685 people after a first episode suggestive of MS (clinically isolated syndrome). In that group, a positive result was linked to much higher odds of later MS (odds ratio 9.88).
So a negative result does not rule MS out. A positive result is not unique to MS either. The 2025 review notes positive results can occur in other conditions with inflammation in the nervous system. Our page on MS, vitamin D and omega-3 covers the wider diagnostic criteria.
IIH is raised pressure around the brain with no known cause. It can cause headaches and vision problems. The NHS says tests usually include a brain scan and a lumbar puncture to check the pressure.
UK consensus guidelines say people with papilloedema, swelling at the back of the eye, should have a lumbar puncture after normal imaging (Mollan et al., JNNP 2018). The "opening pressure" is measured while you lie on your side. Diagnostic criteria use a cut-off above 25 cm of CSF. The guidelines say the number should not be read in isolation. Our guide to migraine, tension and cluster headaches covers more common headache types.
When a dementia diagnosis is uncertain and Alzheimer's is suspected, NICE says doctors can consider testing CSF for tau and amyloid beta (NICE NG97). FDG-PET scanning is the alternative. NICE warns that the older a person is, the more likely a false positive CSF result becomes. For suspected rapidly progressive dementia, NICE advises referral to a neurology service that can test CSF for Creutzfeldt–Jakob disease.
Blood tests for Alzheimer's markers are changing this picture. Our article on what happens in the brain in Alzheimer's explains those changes. Our page on mild cognitive impairment covers what amyloid results can and cannot predict.
CSF testing is used in some sleep disorders too. Our guide to why narcolepsy diagnosis takes years explains the CSF hypocretin test. The NHS also notes lumbar puncture is used to give medicines, such as treatment for some infections or cancers, and spinal anaesthetics.
The NHS describes lumbar puncture as usually very safe. In adults, the needle goes in below the level where the spinal cord ends.
Some situations need care first. In suspected meningitis, NICE says doctors should not routinely scan the brain before a lumbar puncture (NICE NG240). But they should scan first, and delay the procedure, if there are signs of raised pressure inside the head. These include new focal neurological signs, seizures, abnormal pupils or a reduced level of consciousness. NICE also says not to do it if there is infection at the needle site or a rapidly spreading rash. Bleeding risk should be corrected first.
That is why you may be asked to stop certain medicines, such as blood thinners, beforehand. Only do this on your doctor's instructions.
The NHS describes the steps:
It usually takes 15 to 20 minutes, but can take longer. It should feel uncomfortable, not painful. Tell the doctor if it hurts. If you are anxious about needles, say so. Afterwards, you will usually be monitored for one to two hours. Outpatients can usually go home after a few hours.
The best-known side effect is post-dural puncture headache. The International Headache Society defines it as a headache within five days of the procedure, caused by CSF leaking through the needle hole (ICHD-3). Headaches from low CSF pressure are typically orthostatic: worse when upright and eased by lying down (ICHD-3). Neck stiffness or hearing symptoms are common with it. It usually settles within two weeks on its own. If not, it can be treated by sealing the leak with a "blood patch", an injection of your own blood.
How often it happens depends partly on the needle:
Atraumatic needles have a rounded tip that parts tissue rather than cutting it. Ask which type your hospital uses.
In the memory-clinic study, 31% reported some complaint afterwards. Back pain affected 17% and any headache 19%, but only 0.7% were admitted to hospital. A history of headache was the biggest risk factor. Being over 65 and an atraumatic needle were protective.
ICHD-3 lists other risk factors: being female, being aged 31 to 50, and a previous post-dural puncture headache.
Probably not. A Cochrane review of 24 trials with 2,996 people compared bed rest with getting up straight away (Arevalo-Rodriguez et al., Cochrane 2016). Bed rest did not prevent headache, and may have slightly increased it (relative risk 1.24). Whether extra fluids help remains unclear. The memory-clinic study also found rest made no difference.
The NHS still advises resting for 24 hours, drinking plenty of fluids, and lying flat if you get a headache. Lying down may ease a headache once it has started. Follow your own hospital's instructions.
The NHS lists common side effects that usually go within a few days:
It describes complications as extremely rare. They include long-term back pain, infection, nerve damage, hearing loss, double vision and blood clots.
Get urgent advice from your GP, out-of-hours service or the hospital team if you have severe pain or a headache that won't go away. The same applies to a high temperature, unusual sweating, or a wound leaking for more than a week. In the UK, NHS 111 can help.
Call an ambulance (112 or 999 in Ireland, 999 in the UK, 911 in the US) if your arms or legs feel weak or numb. Also call if you have problems peeing or pooing, or feel confused.
The NHS says diagnostic results may come back in a few days, but can take a few weeks. Urgent tests, such as for meningitis, are processed much faster. Specialist tests, such as OCBs or dementia markers, often take longer. You may need a follow-up appointment.
A result is one part of the picture. A raised opening pressure needs context. OCBs are not unique to MS. Dementia markers can give false positives in older people. Ask the specialist what your results mean for you.
A lumbar puncture is a specialist test, done in hospital.
In Ireland and the UK, it is arranged by a hospital consultant, often a neurologist, or done in the emergency department. The NHS says you will usually be referred by a consultant or specialist. It is not something you can request directly from your GP.
In the US, it is ordered by a physician, often a neurologist or emergency doctor. We have not checked US costs.
Don't wait for a test appointment if you have a sudden, very painful headache unlike anything before. The same goes for a headache with fever, stiff neck, confusion, seizures or a rash. The HSE says to call 112 or 999 in Ireland. In the UK call 999, and in the US call 911.
You will have a local anaesthetic, so it should not be painful. The NHS says you may feel pressure, discomfort or brief pins and needles. Tell the doctor if you are in pain.
Serious nerve damage is extremely rare, according to the NHS. In adults, the needle goes in below where the spinal cord ends. Call an ambulance if your legs feel weak or numb afterwards.
The NHS advises resting for 24 hours and avoiding heavy lifting or sport until you feel well enough. Some people take longer to recover. Ask your team, especially if your job is physical.
MRI shows structure. CSF shows infection, bleeding, pressure and inflammation that scans can miss. In suspected bleeding around the brain, a lumbar puncture may follow a normal CT done more than six hours after the headache began.
It means no bands were found. It does not rule out MS, because about 1 in 8 people with MS do not have them. Your neurologist will weigh it alongside your MRI and symptoms.
This article is general information, not medical advice. It does not replace advice from your GP, neurologist or hospital team. Do not stop any medicine before a procedure unless your doctor tells you to.
Reviewed by: Proco Team
Last updated: November 2026