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Pediatric Cancer — Diagnosis & Tests
Lumbar puncture in children — why and what to expect
Medically reviewed by Dr. Muralidhar Muddusetty, MS (Surgical Oncology) · Last reviewed June 2026
Hearing that your child needs a lumbar puncture — or spinal tap — can feel frightening. Most children tolerate it well, and it is one of the most important tests for understanding whether cancer has reached the fluid around the brain and spinal cord. This page explains exactly what a lumbar puncture involves, why it matters, and how to prepare your child and yourself.
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Understanding the procedure
What is a lumbar puncture — and why does my child need one?
A lumbar puncture (also called a spinal tap) is a procedure that removes a small amount of fluid from the space around the spinal cord. That fluid — called cerebrospinal fluid, or CSF — bathes and cushions the brain and spinal cord. Analysing it tells the oncology team things a blood test or scan cannot.
The fluid itself matters. Cerebrospinal fluid circulates around the brain and spinal cord in a closed system. In certain childhood cancers — particularly leukaemia and some brain tumours — cancer cells can enter this system. A blood test cannot detect this. The only reliable way to check is to sample the CSF directly through a lumbar puncture.
In childhood leukaemia, a spinal tap is a standard diagnostic step. Acute lymphoblastic leukaemia (ALL), the most common childhood cancer, can involve the central nervous system. Checking the CSF at diagnosis — and at key points during treatment — tells the team whether leukaemia cells have reached the brain and spinal cord. This directly affects which treatment protocol your child follows.
It is also used in brain tumour cases. When a child has a tumour in or near the brain, the CSF may carry shed tumour cells that have spread along the spinal cord. Lumbar puncture results help the team stage the disease — understanding how far it has travelled — and plan treatment accordingly.
The procedure is also used to deliver treatment, not just to diagnose. In some leukaemia protocols, after checking the CSF, the doctor may inject a small amount of treatment directly into the spinal fluid at the same sitting. This is called intrathecal therapy. It targets any cancer cells that might be present in the CNS and that systemic treatment may not reach as effectively.
A lumbar puncture is not the same as surgery. No general anaesthetic is required in most cases (though sedation is commonly used for children). No cut is made. The needle is thin, the sample taken is small, and the child can usually return home the same day.
What the CSF test checks for
Cancer cells
CNS involvement
Microscopic examination looks for leukaemia or tumour cells in the fluid. Finding them changes the treatment plan.
Cell counts
White cell count in CSF
Elevated white cells can indicate inflammation, infection, or cancer cell infiltration of the central nervous system.
Chemistry
Protein & glucose
Abnormal protein or glucose levels in the CSF can point to tumour activity or infection alongside cancer treatment.
Flow cytometry
Cell typing
In leukaemia, flow cytometry identifies the exact type of leukaemia cells present in the CSF — guiding targeted therapy.
Pressure
Opening pressure
The pressure at which fluid flows through the needle is measured. High pressure can indicate a blockage or inflammation.
Culture
Infection screen
Children on cancer treatment are at higher infection risk. CSF can be tested for bacteria or fungi when an infection is suspected.
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Step by step
What to expect before, during, and after your child's lumbar puncture
Knowing exactly what will happen helps parents feel more prepared — and a calmer parent helps a child feel calmer too. Here is a typical sequence for a paediatric lumbar puncture in an oncology setting.
Preparation: what to do the day before and morning of
If your child will be sedated or have a general anaesthetic, you will be given nil-by-mouth instructions — typically no food or milk for several hours before the procedure, and no clear fluids for two hours before. Follow these exactly; eating before sedation increases the risk of complications. Bring any comfort items your child finds reassuring — a favourite toy, a blanket, music on a phone. Wear comfortable, loose clothing so the lower back is accessible without fully undressing. Arrive a little early so your child can settle in the ward before the team comes.
Numbing cream applied at least an hour before
A local anaesthetic cream (such as EMLA) is applied to the skin of the lower back under a small dressing. It needs at least 45 to 60 minutes to take full effect. This step is why lumbar punctures in children hurt far less than parents expect — the skin is genuinely numb before the needle is placed. While waiting, the team will check your child's blood count and clotting levels if not done recently, and a nurse will explain the procedure and answer questions. This is a good time to ask anything you have been thinking about.
Positioning your child for the procedure
There are two positions used: lying curled on one side (like a foetal position, drawing the knees toward the chest) or sitting on the edge of the bed hunched forward over a pillow. Both are designed to open the spaces between the vertebrae so the needle can pass through safely. A nurse or a parent (if present) usually helps the child hold still in this position. Staying still is the most important thing your child can do — moving during needle placement increases discomfort and the risk of the needle needing to be repositioned.
The CSF sample is collected
After the skin is cleaned with antiseptic, the doctor injects a small amount of local anaesthetic into the deeper tissue. The spinal needle is then advanced into the subarachnoid space — the fluid-filled area around the spinal cord — between the third and fourth or fourth and fifth lumbar vertebrae (well below the point where the spinal cord itself ends). Your child may feel pressure or a brief ache in the lower back or down one leg; this is normal. Several small vials of CSF are collected — the total amount removed is tiny and the body replaces it within hours. If intrathecal therapy is being given, the doctor will inject the treatment directly into the same space at this point before the needle is removed.
Recovery: lying flat and watching for a headache
After the needle is removed and a dressing applied, your child will lie flat for 30 to 60 minutes. This reduces the chance of a post-lumbar-puncture headache by giving the small needle-hole time to seal. Encourage your child to drink fluids once they are allowed — this helps the body replenish CSF quickly. Some children feel a dull back ache at the needle site for a day or two; a warm compress and rest help. If your child develops a headache that is noticeably worse when sitting or standing and better when lying down, tell the care team — this is the classic pattern of a post-LP headache and can usually be managed at home with rest and fluids, though occasionally a short hospital visit is needed.
When to seek medical attention after discharge
Most children go home the same day. Contact the hospital immediately if your child develops a fever above 38°C, severe or worsening headache not relieved by lying flat, redness or swelling at the needle site, difficulty walking or weakness in the legs, or neck stiffness with a high fever. These are uncommon but are signs that need prompt evaluation. Otherwise, your child can resume normal gentle activity within 24 hours. The oncologist will review the CSF test results with you, typically within one to five working days depending on which tests were requested.
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Common questions
Your questions about lumbar puncture in children — answered
Is a lumbar puncture painful for a child?
Most children do not find a lumbar puncture as painful as they fear. In paediatric practice, the procedure is almost always done with a local anaesthetic cream applied to the skin well before the needle is inserted, and in younger children or those who are very anxious, a short-acting sedative or general anaesthetic may be used. The most uncomfortable moment is typically the local anaesthetic injection, which stings briefly. After that, the deeper needle is inserted while the local anaesthetic takes effect. Your child may feel pressure or a mild ache in the back or down one leg — this is normal and passes quickly. The whole procedure usually takes 20 to 30 minutes from start to finish. Afterwards, a short period of lying flat helps reduce the chance of a headache.
What is the doctor looking for in the CSF test after a lumbar puncture?
The cerebrospinal fluid (CSF) collected during a lumbar puncture in a child with suspected or confirmed cancer is examined in several ways. The laboratory checks for cancer cells — in leukaemia, for example, this is called looking for central nervous system (CNS) involvement, meaning whether leukaemia cells have entered the fluid around the brain and spinal cord. The CSF is also checked for white cell count, protein and glucose levels, and the presence of any infection. In children with brain or spinal cord tumours, the CSF may contain shed tumour cells. The results from a CSF test guide treatment decisions — particularly whether treatment needs to be directed at the brain and spinal cord in addition to the rest of the body.
Why does a child with leukaemia need a spinal tap?
A spinal tap — the same procedure as a lumbar puncture — is a standard part of diagnosing and treating childhood leukaemia. Leukaemia cells can travel through the bloodstream into the cerebrospinal fluid that surrounds the brain and spinal cord. This is called CNS (central nervous system) involvement. The spinal tap allows the doctor to look directly at the CSF to find out whether leukaemia cells have reached the CNS. This matters enormously for treatment planning: if CNS involvement is found, treatment will include steps aimed specifically at clearing leukaemia cells from the spinal fluid. Even if no cancer cells are found at diagnosis, preventive treatment into the spinal fluid is usually given as part of standard leukaemia treatment protocols to keep the CNS safe throughout therapy.
How long does it take to get lumbar puncture results?
The time varies depending on what is being tested. A basic count of cells in the CSF and a glucose-protein check can be available within a few hours of the procedure. Looking for cancer cells under a microscope — called a CSF cytology or cytospin — usually takes one to two working days, since the fluid needs to be spun down and the slide prepared carefully. More detailed tests, such as flow cytometry to identify specific types of leukaemia cells, may take two to five days. Your child's oncologist will let you know the expected turnaround and will call you as soon as the results are available. Results are discussed in the context of all other test findings — a lumbar puncture result is never interpreted alone.
What are the risks and side effects of a lumbar puncture in a child?
Lumbar puncture is a well-established, commonly performed procedure in children. The most common side effect is a post-lumbar-puncture headache, which occurs because a small amount of spinal fluid can leak through the needle site, temporarily reducing the cushioning around the brain. Lying flat for a period after the procedure reduces this risk. The headache, if it occurs, is usually positional — worse when sitting or standing, better when lying down — and improves over one to two days with rest and fluids. Other rare risks include localised back soreness, a small bruise at the needle site, or, very rarely, infection. Serious complications are uncommon in experienced paediatric hands. Your care team will explain all risks and how to monitor your child at home after the procedure.
Can I stay with my child during the lumbar puncture?
In most paediatric oncology centres, one parent or caregiver is welcome to stay close to the child during the preparation — holding their hand, talking to them, or helping them stay still with calm reassurance. Whether you remain in the room during the needle insertion itself depends on the hospital's policy, your child's age, the level of sedation being used, and what you yourself are comfortable with. For procedures done under general anaesthesia, parents wait outside the room until the child is ready to be brought to the recovery area. Being present during preparation and recovery makes a real difference to how calm and safe a child feels. Ask your nurse coordinator ahead of time what the usual practice is at your centre, so there are no surprises on the day.
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