A lumbar puncture is the insertion of a needle into the subarachnoid space to measure intracranial (opening) pressure, drain cerebrospinal fluid (CSF), and administer intrathecal medications.
- Indications
- Diagnostic lumbar puncture
- Meningitis
- Encephalitis
- Subarachnoid haemorrhage
- Multiple sclerosis
- Gullain-Barre syndrome
- Malignancy
- Therapeutic
- Intrathecal antibiotics, chemotherapy, or analgesis
- CSF drainage to reduce ICP in some conditions
- Subarachnoid haemorrhage
- Cryptococcal meningitis
- Diagnostic lumbar puncture
- Contraindications
- Absolute contraindications
- Infection at the puncture site
- CNS space-occupying lesions with risk of cereral herniation
- Significant coagulopathy
- Severe thrombocytopaenia (PLT < 20,000)
- Relative contraindications
- Anticoagulation (UFH/LMWH within 24 hours)
- Antiplatelet therapy
- Obesity
- Scoliosis
- Degenerative spinal disease
- Absolute contraindications
- Indications for Head CT scan before LP
- Altered mental status
- Focal neurological deficits
- New-onset seizure
- Papilloedema
- Immunocompromised state
- Malignancy
- Age > 60 years
- When there is concern for raised ICP
- Procedure
- Review history/physical exam. Head CT-scan if indicated.
- Informed consent
- Position
- Lateral decubitus in a fetal position. This allows accurate opening pressure.
- Sitting position is less reliable for opening presure
- Site
- Supracristal plane (Tuffier line) at L3/L4 or L4/L5
- This is below the conus medullaris
- Sterile preparation and draping
- Local anaesthesia
- Insert spinal needle with stylet in midline aiming approximately towards the umbilicus
- If bone is encountered withdraw to subcutaneous tissue before redirecting
- Once CSF flows measure opening pressure if indicated
- Allow CSF to drain passively and collect samples ( 3 – 4 vials each 1mL)
- Replace the stylet before removing the needle
- CSF analysis
- Appearance
- Normal is clear or colourless
- Xanthochromia in SAH, hyperbilirubinaemia or traumatic tap
- Turbid or cloudy due to increased cells/proteins
- Opening pressure
- Normal is ~ 6 – 25 cm H2O
- WBC/Differential
- Normal is 0 – 5 cells/uL
- Neutrophilia = bacterial
- Lymphycytosis = viral/TB/fungal
- Protein
- Normal is ~ 15 – 45 mg/dL
- Glucose
- Normal is ~ 2.5 – 4.4 mmol/L (60% of serum glucose)
- Gram stain/culture
- TB testing (AFT, GeneXpert, or culture)
- Cryptococcal antigen
- PCR
- Cytology for malignancy
- Appearance
- Complications
- Post-dural puncture headache (PDPH)
- A 22 G pencil-point needle (Whitacre) is preferred over the cutting (Quincke) needle since it reduces PDPH
- Traumatic tap
- False elevation of CSF WBC making it difficult to distinguish traumatic tap from SAH
- Back pain
- Infection
- Bleeding
- Spinal hematoma
- Severe persistent back pain
- New weakness or sensory symptoms
- Sphincter dysfunction
- Cerebral herniation
- Post-dural puncture headache (PDPH)
Classic CSF patterns
| Condition | WBC / differential | Protein | Glucose | Opening pressure |
|---|---|---|---|---|
| Normal CSF | 0–5/µL | 15–45 mg/dL | 45–80 mg/dL or ~60% serum | 6–25 cm H₂O |
| Bacterial meningitis | 100–10,000/µL, predominantly neutrophils | 100–500 mg/dL | <40 mg/dL or <40% serum | >25 cm H₂O |
| Viral meningitis | 10–1,000/µL, predominantly lymphocytes | 50–100 mg/dL | Usually normal, 40–80 mg/dL | Normal or mildly ↑ |
| TB meningitis | 10–500/µL, predominantly lymphocytes | 100–500 mg/dL | <45 mg/dL or <40% serum | ↑, often >25 cm H₂O |
| Fungal meningitis | 10–500/µL, usually lymphocytes | 100–500 mg/dL | <40 mg/dL | ↑ |
| Subarachnoid hemorrhage (SAH) | RBCs often thousands–hundreds of thousands/µL | ↑ | Usually normal | ↑ |
| Gullain-Barre syndrome (GBS) | <5/µL | >45 mg/dL, often 100–500+ | Normal | Usually normal |