What is a normal CSF result?

In adults, normal CSF has fewer than 5 white cells per microlitre, all mononuclear, a protein of 0.15 to 0.45 g/L, and a CSF to serum glucose ratio above 0.6. Values outside these ranges suggest an inflammatory or infectious process.

How does the tool tell bacterial from viral meningitis?

Bacterial meningitis typically shows a high neutrophil-predominant cell count, high protein, and a low glucose ratio below 0.4. Viral meningitis shows a lower lymphocyte-predominant count with normal glucose and only mildly raised protein. The tool matches your values to these signatures.

Why is the CSF:serum glucose ratio more useful than CSF glucose alone?

CSF glucose tracks blood glucose, so a low CSF glucose in a hyperglycaemic patient may still be normal. The ratio corrects for serum glucose and is a more reliable marker of consumption by bacteria, TB, or fungi, where it falls below 0.5.

What pattern suggests tuberculous or fungal meningitis?

A lymphocyte-predominant pleocytosis combined with a low glucose ratio and a high — sometimes very high — protein points to TB or fungal meningitis. These warrant AFB stain and culture, TB-PCR, cryptococcal antigen, and India ink testing.

Can I rely on the CSF pattern alone to decide treatment?

No. Patterns overlap, and early or partially treated bacterial meningitis can mimic a viral picture. Never withhold empirical antibiotics on CSF figures alone; always combine them with the clinical picture, Gram stain, culture, and PCR.

What is the CSF Analysis Interpreter?

Enter CSF white cell count, neutrophil predominance, protein, and glucose with serum glucose to get a pattern-based meningitis differential covering bacterial, viral, TB, and fungal causes, plus the CSF:serum glucose ratio. It runs free in your browser on Gera Tools, with nothing uploaded.

CSF Analysis Interpreter

Name: CSF Analysis Interpreter
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

Cerebrospinal fluid analysis is the central test in suspected meningitis. The combination of cell count, cell type, protein, and the glucose ratio produces recognisable patterns that point toward a bacterial, viral, tuberculous, or fungal cause. This tool maps your values onto those patterns.

The four parameters and what each one tells you

White cell count (WBC per µL) is the most direct marker of CNS inflammation. A normal CSF contains fewer than 5 cells per µL in adults. Bacterial meningitis typically drives this into the hundreds to thousands; viral meningitis produces a more modest pleocytosis usually in the tens to low hundreds.

Cell differential (neutrophil % vs. lymphocyte %) is often the first branch point in the differential. Neutrophil predominance strongly suggests a bacterial cause. Lymphocyte predominance is more consistent with viral, TB, fungal, or partially treated bacterial meningitis. A mixed picture can occur in early bacterial infection before neutrophils fully dominate.

Protein (g/L) rises in proportion to the severity of inflammation and blood-brain barrier disruption. Normal is roughly 0.15–0.45 g/L. Bacterial meningitis often exceeds 1 g/L; TB meningitis can reach very high levels. Viral meningitis typically produces only mild protein elevation, often still within or just above the normal range.

CSF:serum glucose ratio is more informative than CSF glucose alone because blood glucose is the substrate. The ratio is calculated as CSF glucose ÷ serum glucose. A ratio above 0.6 is normal. Bacteria and fungi consume glucose, so bacterial, fungal, and TB meningitis typically drive the ratio below 0.4–0.5. Viral meningitis leaves glucose essentially normal.

How it works

The interpreter computes the CSF:serum glucose ratio and then matches the overall picture against classic signatures:

Bacterial  WBC >500, neutrophil-predominant, protein >1 g/L, ratio <0.4
Viral      WBC 10–500, lymphocyte-predominant, normal glucose, mild protein
TB/Fungal  lymphocyte-predominant, ratio <0.5, protein high to very high
Normal     WBC <5, protein <0.45 g/L, ratio >0.6

The glucose ratio is calculated as CSF glucose ÷ serum glucose, which corrects for the patient’s blood sugar and is far more reliable than CSF glucose read in isolation.

A worked example

Consider a CSF with WBC 820/µL (90% neutrophils), protein 1.8 g/L, CSF glucose 1.2 mmol/L, serum glucose 5.8 mmol/L:

Ratio: 1.2 ÷ 5.8 ≈ 0.21 (well below 0.4)
Very high neutrophil-predominant pleocytosis + high protein + low ratio → classic bacterial meningitis pattern
Immediate Gram stain, culture, and empirical antibiotic cover is indicated

By contrast, if the WBC were 85/µL (80% lymphocytes), protein 0.6 g/L, and ratio 0.7, the picture would be far more consistent with a viral cause — though partially treated bacterial meningitis remains on the differential.

Notes and cautions

These patterns are typical, not absolute. Early bacterial meningitis can present with a near-normal or lymphocytic picture, and prior antibiotics blunt the classic findings of a partially treated infection. The tool is a structured aid to the differential — it does not replace Gram stain, culture, PCR, and clinical judgement, and empirical therapy should never be delayed while awaiting these results.

Additional investigations to consider alongside CSF analysis include: Gram stain and bacterial culture, meningitis/encephalitis PCR panel, cryptococcal antigen (especially in immunocompromised patients), AFB smear and mycobacterial culture for TB, and India ink if cryptococcal meningitis is suspected.