A CSF Analysis (Biochemistry & Cell Count) is a laboratory test performed on cerebrospinal fluid (CSF)—the clear fluid that surrounds and protects the brain and spinal cord. The sample is usually collected through a lumbar puncture (also called a “spinal tap”), where a clinician carefully withdraws a small amount of spinal fluid from the lower back.

This test focuses on two main areas:

• Biochemistry: measures key chemical components in CSF, most commonly glucose and protein.
• Cell count: measures the number of white blood cells (WBCs) and red blood cells (RBCs) in the CSF (often with a differential to see what types of WBCs are present).

In plain language, the results help doctors understand whether there is infection, inflammation, or bleeding involving the brain/spinal cord:

• CSF white blood cells (WBCs): Higher-than-normal WBCs often suggest infection (such as meningitis) or other inflammatory conditions. The type of WBCs can provide clues (for example, neutrophils may be seen more in some bacterial infections).
• CSF red blood cells (RBCs): RBCs in CSF may indicate bleeding around the brain (such as subarachnoid hemorrhage). Sometimes RBCs appear due to a “traumatic tap” (minor bleeding from the needle during the lumbar puncture), so clinicians interpret RBC results in context.
• CSF protein: Elevated protein can occur with infection, inflammation, bleeding, nerve disorders, or disruption of the blood–brain barrier. Very low protein is less common and is usually interpreted alongside other findings.
• CSF glucose: Low CSF glucose (especially compared to blood glucose) can be seen in certain infections (classically some bacterial, fungal, or TB infections) and other inflammatory processes. Normal glucose does not rule out all infections.

CSF testing is typically interpreted together with other studies (such as CSF culture, PCR tests for viruses, imaging, and blood tests) because no single CSF value alone provides the full diagnosis.

Doctors most often order CSF biochemistry and cell count when symptoms suggest a condition affecting the brain, spinal cord, or the tissues around them (the meninges). It is commonly part of an urgent evaluation for meningitis or other serious neurologic conditions.

This test may be recommended if you have symptoms such as:

• Fever with severe headache
• Neck stiffness or pain when bending the neck
• Confusion, unusual sleepiness, or changes in mental status
• Light sensitivity (photophobia)
• Seizures
• Nausea/vomiting with a severe headache
• Sudden “worst headache of life” (a concern for bleeding such as subarachnoid hemorrhage)

It may also be ordered to help evaluate or monitor conditions such as:

• Suspected central nervous system infection (bacterial, viral, fungal, or tuberculosis-related)
• Autoimmune or inflammatory neurologic diseases
• Unexplained neurologic symptoms (for example, weakness, numbness, vision changes) when clinicians need to assess for inflammation in the nervous system
• Possible bleeding around the brain, especially if imaging is inconclusive

Certain risk factors may increase the urgency for CSF testing, including a weakened immune system, recent serious infection, recent neurosurgery, exposure to meningitis, or symptoms in infants/older adults where meningitis can present atypically.

• Meningitis (bacterial, viral, fungal)
• Encephalitis
• Subarachnoid hemorrhage (bleeding around the brain)
• Multiple sclerosis and other inflammatory demyelinating disorders
• Tuberculous meningitis
• Neuroborreliosis (Lyme disease involving the nervous system)
• Guillain–Barre9 syndrome (often assessed with CSF protein findings alongside other tests)
• Cancer involving the central nervous system (e.g., leptomeningeal spread; usually evaluated with additional CSF tests such as cytology)

• Rapid identification of serious infection (supporting timely treatment of meningitis/other CNS infections)
• Clarifying the cause of severe headache (including evaluation for bleeding or inflammation)
• Assessing brain/spinal cord inflammation to guide diagnosis and next-step testing
• Monitoring neurologic autoimmune or inflammatory conditions when CSF findings are part of the overall clinical picture
• Supporting safe, targeted care by helping clinicians decide on antibiotics/antivirals and the need for hospital monitoring