Time- and threshold-dependent cerebrospinal fluid protein elevation and albuminocytologic dissociation in Guillain-Barré syndrome: a systematic review and meta-analysis.

BACKGROUND: Cerebrospinal fluid (CSF) protein elevation and albuminocytologic dissociation (ACD) are supportive features in Guillain-Barré syndrome (GBS), but their yield may depend on lumbar puncture timing and protein-threshold definition. METHODS: We registered the protocol in PROSPERO (CRD420261442200) and searched PubMed, Embase, Web of Science Core Collection, and Cochrane CENTRAL till 5th July 2026. Eligible studies reported extractable CSF protein elevation or ACD data in GBS-spectrum disorders. Records were screened and extracted independently. Random-effects logit models were used for pooled proportions. RESULTS: Twenty-four studies were included and 19 contributed quantitative data. In 12 main cohorts including 2966 patients, the pooled study-defined CSF protein elevation or ACD yield was 79.6% (95% confidence interval [CI] 70.4-86.5; I2 = 96.3%). Yield was lower during the first 0-1 days after onset (48.1%) and higher after the first week. Fixed 0.45 g/L thresholds gave a higher apparent yield than age-adjusted or age-dependent thresholds (69.5% vs 50.0%). CONCLUSIONS: CSF protein elevation and ACD are common supportive findings in GBS but their interpretation depends on timing and threshold definition. A normal CSF protein result during the first days after symptom onset does not exclude GBS. Conversely, a fixed low threshold may classify more results as abnormal than an age-adjusted reference limit. Timing and the threshold used should be reported when CSF findings are used to support the diagnosis. TRIAL REGISTRATION: PROSPERO registration: CRD420261442200.