β‐Trace protein in cerebrospinal fluid: A blood–CSF barrier–related evaluation in neurological diseases

β‐Trace protein concentrations in cerebrospinal fluid (CSF) and serum from 113 patients with variuos neurological diseases and 65 controls were determined with a sensitive and specific immunonephelometric assay. In adult control patients, β‐trace concentrations were 14.6 ± 4.6 mg/L in CSF and 0.46 ± 0.13 mg/L in serum, that is 32‐fold higher in CSF. β‐trace levels in CSF correlated with age as well as with the albumin CSF/serum ratio (Q A1b ), which is considered a measure for blood‐CSF barrier function. The relationship between CSF β‐trace levels and elevated Q A1b values was studied in various neurological diseases with CSF protein increase. In spinal canal stenosis, CSF β‐trace (mean = 29.5 ± 10.5 mg/L) correlated positively with increasing Q A1b values. In bacterial meningitis, CSF β‐trace (mean = 8.7 ± 3.9 mg/L) remained invariant to changes of Q A1b values. In Guillain‐Barre syndrome, CSF β‐trace (mean = 14.4 ± 6.8 mg/L) was below the Q A1b ‐dependent reference range. In multiple sclerosis and viral meningoencephalitis, β‐trace levels were within the reference range. β‐Trace concentration in CSF can be used in conjunction with Q A1b to distinguish between different neurological pathologies associated with CSF protein increase.