Medicine – Cerebrospinal Fluid (CSF) Findings

Cerebrospinal fluid (CSF) analysis is particularly useful when investigating meningitis, encephalitis, inflammatory neurological disease, and demyelinating disorders such as multiple sclerosis.

The major features to assess are opening pressure, appearance, glucose, protein, white-cell count and differential, microbiology, and—when appropriate—oligoclonal bands and other specialised tests.

A particularly useful examination pattern is:

Bacterial meningitis → neutrophils + low glucose + very high protein.

Viral meningitis → lymphocytes + normal glucose + moderately raised protein.

TB meningitis → lymphocytes + low glucose + high protein.

Multiple sclerosis → oligoclonal bands + raised IgG index, with glucose usually normal.

1. Normal CSF

Normal CSF is clear and colourless, often described as having a crystal-clear appearance.

There should be very few white blood cells, with normal adult CSF generally containing approximately 0–5 white cells/µL, predominantly mononuclear cells.

Normal CSF Glucose

CSF glucose is normally approximately 60–70% of the simultaneous plasma glucose concentration.

The image gives approximately one-half to two-thirds of blood glucose, which is a useful traditional approximation.

Interpretation is more reliable when CSF glucose is compared with a blood glucose measurement obtained around the time of lumbar puncture.

Normal CSF Protein

Normal CSF protein is relatively low.

The image gives approximately:

0.2–0.4 g/L.

Exact reference ranges vary according to the laboratory, patient age, and sampling site.

Normal CSF Opening Pressure

Opening pressure should be measured with the patient appropriately positioned, usually in the lateral decubitus position.

The image gives an older normal range of approximately 60–150 mmH₂O.

Modern adult reference ranges are often somewhat broader, with values around 60–250 mmH₂O frequently used depending on the clinical setting and measurement technique.

Therefore, opening pressure should always be interpreted in clinical context.

2. Acute Bacterial Meningitis

Acute bacterial meningitis produces an intense inflammatory response within the meninges and CSF.

The characteristic pattern is:

Turbid CSF + neutrophils ↑↑ + protein ↑↑ + glucose ↓.

Appearance

CSF may appear turbid or purulent because of the large number of inflammatory cells, organisms, and increased protein.

However, CSF appearance alone cannot reliably confirm or exclude bacterial meningitis.

Glucose

CSF glucose is characteristically low.

This reflects consumption of glucose by inflammatory cells and microorganisms together with impaired glucose transport across the inflamed blood-CSF barrier.

A low CSF-to-blood glucose ratio is particularly helpful.

Protein

CSF protein is usually markedly elevated because inflammation disrupts the blood-CSF barrier and allows increased protein to enter the CSF.

Therefore:

Bacterial meningitis → very high protein.

White Cells

The white-cell count is usually substantially increased, often into the hundreds or thousands of cells/µL.

The predominant cells are usually neutrophils (polymorphs).

The image gives approximately 200–3000 polymorphs/mm³, but exact counts vary widely and should not be treated as rigid diagnostic boundaries.

Microbiology

Important investigations include Gram staining and bacterial culture.

Modern assessment frequently also includes molecular/PCR-based testing, depending on local laboratory availability and the suspected organism.

Blood cultures should ideally be obtained because bacteraemia may accompany bacterial meningitis.

Opening Pressure

Opening pressure is commonly raised, although a normal opening pressure does not completely exclude bacterial meningitis.

3. Acute Viral Meningitis

Viral meningitis generally produces a less dramatic CSF disturbance than bacterial meningitis.

The classic pattern is:

Clear CSF + lymphocytes ↑ + protein mildly/moderately ↑ + glucose normal.

Appearance

CSF is usually clear, although mild turbidity can occasionally occur when the cell count is high.

Glucose

CSF glucose is usually normal.

This is one of the most useful differences between typical viral and bacterial meningitis.

Therefore:

Viral → normal glucose.

Bacterial → low glucose.

There are exceptions, so the complete clinical and laboratory picture remains important.

Protein

CSF protein is usually mildly to moderately elevated, rather than reaching the very high levels often seen in bacterial or tuberculous meningitis.

White Cells

A lymphocytic/mononuclear pleocytosis is characteristic.

The image gives approximately 10–100 mononuclear cells/mm³, although viral meningitis can produce substantially higher counts.

Early in some viral infections, particularly during the first hours of illness, neutrophils may temporarily predominate before the CSF becomes lymphocyte-predominant.

Microbiology

Modern diagnosis commonly relies on CSF PCR or other nucleic-acid amplification testing for relevant viruses.

Depending on the clinical presentation, organisms tested may include enteroviruses, HSV, VZV, and others.

Serological testing may occasionally have a role but is generally less useful than appropriate molecular testing for many acute CNS viral infections.

4. Tuberculous Meningitis

Tuberculous meningitis is caused by Mycobacterium tuberculosis infection of the meninges.

The characteristic CSF pattern is:

Lymphocytes ↑ + protein ↑↑ + glucose ↓ + opening pressure ↑.

This combination is extremely important for examinations.

Appearance

CSF may be clear, slightly cloudy, or occasionally described as viscous because of the increased protein and inflammatory material.

Historically, CSF left standing could form a delicate “cobweb” clot, although this is not relied upon in modern diagnosis.

Glucose

CSF glucose is usually low, often with a reduced CSF-to-blood glucose ratio.

This means TB meningitis shares low CSF glucose with bacterial meningitis.

Protein

Protein is usually markedly elevated.

Very high CSF protein can occur, particularly when inflammation is severe or CSF flow is impaired.

White Cells

The typical cellular response is lymphocytic/mononuclear pleocytosis.

The image gives approximately 100–300 mononuclear cells/mm³, but considerable overlap occurs.

Importantly, early TB meningitis can occasionally show a more neutrophilic pattern before becoming predominantly lymphocytic.

Microbiology

The image lists acid-fast bacilli using Ziehl–Neelsen staining.

This is correct historically, but direct AFB microscopy has limited sensitivity.

Modern investigation may include:

Mycobacterial culture.

Nucleic-acid amplification/PCR-based testing.

AFB microscopy.

Larger-volume CSF samples can improve microbiological yield.

Opening Pressure

Opening pressure is commonly raised in tuberculous meningitis.

This can result from meningeal inflammation and impaired CSF circulation or absorption, sometimes leading to hydrocephalus.

5. Multiple Sclerosis

CSF analysis in multiple sclerosis (MS) differs considerably from meningitis because MS is a chronic immune-mediated demyelinating disorder rather than a meningeal infection.

Routine CSF appearance and glucose are generally normal.

The major abnormalities involve intrathecal immunoglobulin production.

Appearance

CSF is usually:

Clear and normal in appearance.

Glucose

CSF glucose is generally:

Normal.

A substantially reduced CSF glucose concentration would suggest an alternative diagnosis rather than typical MS.

Protein

Total protein may be normal or mildly elevated.

The image simply describes protein as high, but marked protein elevation is not characteristic of uncomplicated MS and should prompt consideration of another process.

White Cells

CSF may be completely normal or show a mild mononuclear/lymphocytic pleocytosis.

A large white-cell count is unusual and should raise suspicion for infection or another inflammatory neurological disorder.

The image gives 5–50 mononuclear cells/mm³, but typical MS often has fewer cells, and counts above roughly 50 cells/µL would be atypical.

6. Oligoclonal Bands

The classic CSF finding in MS is the presence of CSF-restricted oligoclonal IgG bands.

These indicate intrathecal immunoglobulin synthesis.

The important concept is not simply that oligoclonal bands are “positive,” but that bands are present in CSF in a pattern demonstrating intrathecal production when compared with serum.

7. IgG Index

The CSF IgG index may also be elevated in MS, reflecting increased production of immunoglobulin within the central nervous system.

However, modern diagnosis places substantial importance on CSF-specific oligoclonal bands, interpreted alongside MRI and the clinical presentation.

Neither oligoclonal bands nor an elevated IgG index is completely specific for MS.

8. Normal CSF – Note Form

Appearance: clear and colourless.

Glucose: approximately 60–70% of simultaneous plasma glucose.

Protein: low, approximately 0.2–0.4 g/L in the older reference shown; laboratory ranges vary.

White cells: approximately 0–5 cells/µL.

Opening pressure: depends on technique and patient factors; the older 60–150 mmH₂O range is narrower than many modern adult reference ranges.

9. Acute Bacterial Meningitis – Note Form

Appearance: turbid or purulent.

Glucose: ↓↓↓.

Protein: ↑↑↑.

White cells: markedly ↑.

Predominant cell: neutrophils/polymorphs.

Microbiology: Gram stain, bacterial culture and appropriate molecular testing.

Opening pressure: often ↑.

10. Viral Meningitis – Note Form

Appearance: usually clear.

Glucose: usually normal.

Protein: mildly/moderately ↑.

White cells: ↑.

Predominant cell: lymphocytes/mononuclear cells.

Early disease: neutrophils may occasionally predominate initially.

Microbiology: viral PCR/nucleic-acid testing where appropriate.

Opening pressure: normal or mildly ↑.

11. TB Meningitis – Note Form

Appearance: clear to slightly cloudy; may have increased viscosity.

Glucose: ↓↓↓.

Protein: ↑↑↑.

White cells: ↑.

Predominant cell: lymphocytes/mononuclear cells.

Microbiology: mycobacterial culture + molecular testing ± AFB staining.

Opening pressure: commonly ↑.

12. Multiple Sclerosis – Note Form

Appearance: normal/clear.

Glucose: normal.

Protein: normal or mildly ↑.

White cells: usually normal or mildly increased.

Predominant cells when increased: mononuclear/lymphocytic.

Key finding: CSF-restricted oligoclonal IgG bands.

IgG index: may be ↑.

Opening pressure: usually normal; a significantly raised pressure suggests another or additional diagnosis.

Key Clinical Pattern

The easiest way to remember the CSF patterns is:

Bacterial meningitis

Neutrophils ↑↑↑ + protein ↑↑↑ + glucose ↓↓↓

Viral meningitis

Lymphocytes ↑ + protein ↑ + glucose NORMAL

TB meningitis

Lymphocytes ↑↑ + protein ↑↑↑ + glucose ↓↓↓

Multiple sclerosis

Oligoclonal IgG bands + raised IgG index ± mild lymphocytosis; glucose NORMAL

High-Yield Distinction

Low CSF glucose → think bacterial or TB meningitis.

Normal CSF glucose + lymphocytes → think viral meningitis.

Neutrophils + low glucose → strongly suggests bacterial meningitis.

Lymphocytes + low glucose + very high protein → strongly suggests TB meningitis.

Oligoclonal bands → strongly associated with MS, but not completely specific.