Validated age-specific reference values for CSF total protein levels in children.

OBJECTIVE: To define age-specific reference values for cerebrospinal fluid (CSF) total protein levels for children and validate these values in children with Guillain-Barré syndrome (GBS), acute disseminated encephalomyelitis (ADEM) and multiple sclerosis (MS). METHODS: Reference values for CSF total protein levels were determined in an extensive cohort of diagnostic samples from children (<18 year) evaluated at Erasmus Medical Center/Sophia Children's Hospital. These reference values were confirmed in children diagnosed with disorders unrelated to raised CSF total protein level and validated in children with GBS, ADEM and MS. RESULTS: The test results of 6145 diagnostic CSF samples from 3623 children were used to define reference values. The reference values based on the upper limit of the 95% CI (i.e. upper limit of normal) were for 6 months-2 years 0.25 g/L, 2-6 years 0.25 g/L, 6-12 years 0.28 g/L, 12-18 years 0.34 g/L. These reference values were confirmed in a subgroup of 378 children diagnosed with disorders that are not typically associated with increased CSF total protein. In addition, the CSF total protein levels in these children in the first 6 months after birth were highly variable (median 0.47 g/L, IQR 0.26-0.65). According to these new reference values, CSF total protein level was elevated in 85% of children with GBS, 66% with ADEM and 23% with MS. CONCLUSION: More accurate age-specific reference values for CSF total protein levels in children were determined. These new reference values are more sensitive than currently used values for diagnosing GBS and ADEM in children.

Evaluation of a new immunoassay for chromogranin A measurement on the Kryptor system.

BACKGROUND: Chromogranin A (CgA) is a biomarker for neuroendocrine tumors (NETs). The aims of this study were to evaluate differences in measurement between the ThermoFisher Brahms CgA Kryptor assay and the CisBio assay and to investigate the influence of patient covariates. Temperature stability of CgA using both assays was determined. DESIGN AND METHODS: 406 patients were analyzed for serum CgA using both assays. We performed a comparison study to determine whether several patient covariates (gender, use of protein pump inhibitors, impaired kidney function, referral department and tumor location) influenced the results. For the stability study, pooled serum samples were aliquoted and stored at different storage temperatures (room temperature, 4 °C and -20 °C) until assayed. In addition, 15 individual samples were evaluated after storage at 4 °C using the Kryptor assay. RESULTS: Differences in measured concentrations between the assays were statistically significant. Passing & Bablok fit showed ln Y(Kryptor)=1.05 ln X(CisBio) - 0.20 with a bias of 1.0% after logarithmic transformation. Patient covariates were not associated. Patients׳ sera showed variable stability for CgA in the Kryptor assay at room temperature and 4 °C, whereas the recovery in the CisBio assay was stable at both temperatures. CONCLUSION: Differences in measured CgA concentration between the assays could not be explained by the investigated patient covariates. Serum should be stored at -20 °C prior to determination using the Kryptor assay.