Cerebrospinal fluid (CSF)

When to request this test

• Suspected meningitis or cerebrospinal fluid infection
• Suspicion of acute bacterial meningitis: headache, fever, photophobia, vomiting, neck stiffness, and/or altered level of consciousness

In adults, major causes of bacterial meningitis include: N. meningitidis, S. pneumoniae, L. monocytogenes.

Clinical features may be non-specific in neonates and young infants (e.g. poor feeding, apathy, jaundice, apnoea, full fontanelle, fever, hypothermia) and in older infants may include irritability, drowsiness, poor feeding, high fever, and/or vomiting.

Common bacterial pathogens in neonates and young infants include: Streptococcus agalactiae (Group B streptococcus), E. coli, Klebsiella species, L. monocytogenes, and in older infants and children: S. pneumoniae, H. influenzae, and N. meningitidis.

Acute meningitis may be caused by a range of pathogens, some of which are not bacteria. Microbiologic diagnosis, including bacterial culture from CSF and blood, should be obtained as soon as possible to confirm etiology.

In presentations of subacute or chronic nature, consider diagnostic tests for TB meningitis, particularly in HIV-endemic areas.

Contraindications

Absolute

Blood culture++, then start antibiotics within one hour, and perform a scan before lumbar puncture if:

• Glasgow score <8 or deteriorating/fluctuating level of consciousness
• Signs of raised intracranial pressure: diplopia, abnormal pupillary responses, decerebrate or decorticate posture, low HR + elevated BP + irregular respirations, papilloedema

Relative

Blood culture, then start antibiotics within one hour, and lumbar puncture as soon as possible after patient stabilization:

• Septic shock or haemodynamic compromise (with need of vasopressive agents)
• Significant respiratory compromise eg apnoeic episodes
• New focal neurological signs or seizures
• Seizure within previous 30 min and/or ongoing decreased conscious state following a seizure
• INR >1.5 or platelets <50 x 10⁹/L

Interferences & limitations

• Bacterial contamination by skin flora: use a sterile container for urine and follow careful aseptic sampling procedure
• Antibiotic treatment before sampling can inhibit bacterial growth and skew results
• Haemorrhagic sample may interfere with CSF biochemistry (proteinorachy and glycorachy are then not interpretable)