To assess the frequency of increased cerebrospinal fluid (CSF) total protein levels in patients with Guillain-Barré syndrome (GBS) according to new age-dependent upper reference limit (URL) and disease duration. 

Elevated CSF protein levels are indicative of GBS. However, recent studies showed that the antiquated but still widely used URL for CSF total protein of 0.45 g/L leads to false positive results mainly due to the lack of age-adjustment. 

Patients with GBS who were treated at Medical University of Innsbruck between 2008 and 2018 were included into this retrospective study. Demographic, clinical data and CSF findings were obtained from patients’ medical charts. For statistical analysis, frequency of increased CSF total protein levels depending on time between symptom onset und lumbar puncture (LP) was compared using the conventional URL of 0.45 g/L and a recently published age-dependent URL (determined as the 97.5^th percentile in a large control group comprising more than 6000 CSF samples). 

A total of 70 patients with GBS aged 58±18 years comprising 40% females had CSF sampling within 6 (median; IQR 3-13) days after symptom onset. Median CSF total protein concentration was 0.66 (IQR 0.45-1.03) g/L and correlated with time between symptom onset and LP (r=0.431, p<0.001). Overall, 53 (76%) patients had elevated CSF total protein levels using the conventional URL, whereas 37 (53%) applying the age-dependent URL. Between days 0-3, 4-7, 8-14, 15-21 and thereafter, increased CSF total protein concentrations were found in 52%, 85%, 78%, 100% and 100% of patients using the conventional URL, whereas in 29%, 55%, 67%, 67% and 75% of cases using the age-dependent URL.

Frequency of increased CSF total protein concentration in GBS depends not only on timing of lumbar puncture, but also on patients’ age.