From the Guidelines
A lumbar puncture (LP) shows the composition of cerebrospinal fluid (CSF), providing crucial diagnostic information about conditions affecting the central nervous system, including infections, bleeding, multiple sclerosis, certain cancers, or increased intracranial pressure. The procedure involves collecting CSF by inserting a needle between vertebrae in the lower back. A normal LP reveals clear, colorless fluid with specific ranges for protein (15-45 mg/dL), glucose (50-80 mg/dL or about 2/3 of blood glucose), white blood cells (0-5 cells/mm³), and normal pressure (10-20 cmH₂O) 1.
Key Findings
- Abnormal findings may indicate infections (elevated white cells, low glucose, high protein), bleeding (xanthochromia or red blood cells), multiple sclerosis (oligoclonal bands), certain cancers (malignant cells), or increased intracranial pressure.
- The procedure also helps diagnose meningitis, encephalitis, Guillain-Barré syndrome, and can detect neurodegenerative diseases through biomarkers.
- While generally safe, LPs should be avoided in patients with increased intracranial pressure due to mass lesions, as it could cause brain herniation 1.
- Clinical assessment rather than CT scanning should be used to determine the safety of performing an LP, with specific contraindications including local skin sepsis, clinically unstable patients, and suspicion of spinal cord compression 1.
Contraindications and Precautions
- Contraindications to LP include increased intracranial pressure, coagulopathy, and a skin infection at the site of puncture.
- Patients with a rapidly falling platelet count or those on anticoagulant therapy should be approached with caution.
- A CT scan may be necessary before LP in patients with signs suggestive of a shift of brain compartments, such as focal neurological signs or a reduced Glasgow Coma Scale (GCS) score 1.
Recent Guidelines
- Recent guidelines suggest that LP can be performed without prior neuroimaging if the GCS is >12, but may be safer at lower levels of consciousness 1.
- The UK Joint Specialist Societies guideline recommends delaying LP if any of the following features are present: signs of severe sepsis, respiratory or cardiac compromise, anticoagulant therapy, infection at the site of LP, focal neurological signs, presence of papilloedema, continuous or uncontrolled seizures, or GCS ≤12 1.
From the Research
Lumbar Puncture (LP) Overview
A Lumbar Puncture (LP) is a diagnostic tool used to collect cerebrospinal fluid (CSF) for analysis. The procedure involves inserting a needle between two lumbar vertebrae to collect a sample of CSF.
What LP Shows
LP can show various conditions affecting the central nervous system, including:
- Infections such as meningitis or encephalitis 2, 3
- Inflammatory diseases such as multiple sclerosis or Guillain-Barré syndrome 2, 3
- Subarachnoid hemorrhage or other bleeding disorders 3
- Malignancies such as leptomeningeal carcinomatosis 3
- Immune system disorders such as neurosyphilis or fungal/parasitic infections 3
CSF Analysis
CSF analysis can provide crucial information about the diagnosis of CNS diseases, including:
- White blood cell counts and differential 3
- Protein levels and glucose ratios 3
- Bacterial, viral, or fungal cultures 2, 3
- Polymerase chain reaction (PCR) testing 2, 3
- Protein composition and disease marker discovery 4
Diagnostic Yield
LP is a relatively safe procedure with a high diagnostic yield when performed appropriately 2. However, the procedure may not be necessary for all patients, and extensive testing may not be required for those with normal initial CSF analysis 5.