Situation: A 41-year-old man is admitted to the medical ward with weakness that began in both feet 3 days ago and has now reached his thighs. He had diarrhea 2 weeks earlier. His knee and ankle reflexes are absent, and he reports tingling in both feet. Guillain-Barré syndrome (GBS) is suspected. On the 10th day of his illness, a lumbar puncture is done. Which cerebrospinal fluid (CSF) result supports the diagnosis of GBS?

GBS shows albuminocytologic dissociation: a high CSF protein with a normal cell count. It may be absent in the first week, which is why the test is timed later. Oligoclonal bands point to multiple sclerosis, and low glucose with many neutrophils points to bacterial meningitis.

Core CSF finding in GBS
The cerebrospinal fluid pattern that supports Guillain–Barré syndrome is albuminocytologic dissociation: the protein level rises while the white cell count stays normal. In this patient, the lumbar puncture was deliberately performed on day 10 because this dissociation is often absent during the first week of illness. A large international cohort of 1,231 patients found this pattern in 70% of cases when protein was defined as above 0.45 g/L with fewer than 50 cells/μL ^[4]. A meta-analysis similarly confirms that the diagnostic yield depends on both the timing of the tap and the protein threshold used ^[1].

The elevated protein reflects inflammation and disruption of the blood–nerve barrier at the spinal nerve roots, where the immune attack in GBS is concentrated. Because the pathology is centered on peripheral nerve roots rather than the meninges or brain parenchyma, inflammatory cells do not pour into the CSF in large numbers. This explains the combination of high protein with a normal cell count ^[2].

CSF pattern	Typical condition	Why it differs from GBS
High protein, normal cells	GBS (albuminocytologic dissociation)	Root-level inflammation raises protein without pleocytosis
High white cells, normal protein	Viral meningitis, early infection	Meningeal inflammation draws leukocytes into CSF
Low glucose, high neutrophils	Bacterial meningitis	Bacteria consume glucose and provoke a purulent response
Oligoclonal bands, normal cells	Multiple sclerosis	Intrathecal antibody synthesis within the CNS

Key point! A normal CSF cell count is essential for the diagnosis. In GBS, a cell count above 50 cells/μL should prompt reconsideration of the diagnosis, such as infection, malignancy, or another inflammatory neuropathy ^[3][4]. Watch out! Protein elevation may be missed if the lumbar puncture is performed too early. Repeating the tap after the first week increases the likelihood of detecting albuminocytologic dissociation ^[1][4].

The age of the patient also matters. Because normal CSF protein rises with age, using an age-adjusted upper reference limit can identify albuminocytologic dissociation in older patients who would otherwise fall below the conventional 0.45 g/L cutoff ^[3]. In a 41-year-old man, the conventional threshold is generally appropriate, but the principle of timing remains the dominant clinical consideration.