Age matters: Impact of data-driven CSF protein upper reference limits in Guillain-Barré syndrome.

Objective: We conducted a retrospective review of patients with a diagnosis of Guillain-Barré syndrome (GBS) to assess the diagnostic impact of applying age-adjusted upper limits for CSF total protein (CSF-TP) supported by a systematic literature review. Methods: Cases coded as GBS or inflammatory neuropathy for the period 2001-2016 at The Ottawa Hospital were reviewed. Cases were included if they met the Brighton criteria for GBS with a diagnostic certainty level 1 or 2 and had contemporaneous CSF-TP data. We excluded cases with CSF pleocytosis >50 and cases with Miller-Fisher syndrome. Age-adjusted reference limits were compared with conventional 0.45 and 0.6 g/L upper limits. Results: One hundred thirty-eight cases met the study criteria, with a mean age of 47 years. The mean interval from symptom onset to lumbar puncture was 7.9 days, and mean CSF-TP was 1.23 g/L. There was a strong correlation between rising CSF-TP and time to lumbar puncture. Age-adjusted CSF-TP had a significantly lower sensitivity of only 45% in the first week (32% in the first 3 days) compared with 70% in the first week for the 0.45 g/L limit. All upper limits gained high sensitivity after the first week. Conclusions: The low sensitivity of CSF-TP for the diagnosis of GBS is exacerbated by age-adjusted upper limits. The main role of lumbar puncture in GBS in the first week may be to help exclude other inflammatory or neoplastic etiologies of acute neuropathy. After the first week, the magnitude of the CSF-TP rise reduces the effect of different upper reference limits.