Serum GFAP - pediatric reference interval in a cohort of Danish children.

Objectives: Glial fibrillary acidic protein (GFAP) in blood is an emerging biomarker of brain injury and neurological disease. Its clinical use in children is limited by the lack of a reference interval (RI). Thus, the aim of the present study was to establish an age-dependent continuous RI for serum GFAP in children.

Methods: Excess serum from routine allergy testing of 391 children, 0.4-17.9 years of age, was measured by a single-molecule array (Simoa) assay. A continuous RI was modelled using non-parametric quantile regression and presented both graphically and tabulated as discrete one-year RIs based on point estimates from the model.

Results: Serum GFAP showed a strong age-dependency with declining levels and variability from infants to adolescents. The estimated median level decreased 66 % from four months to five years of age and another 65 % from five years to 17.9 years of age. No gender difference was observed.

Conclusions: The study establishes an age-dependent RI for serum GFAP in children showing high levels and variability in the first years of life.