Figure 3

BDNF increases in plasma frozen at − 20 °C for 12 months. (A) Plasma isolated using K2EDTA tubes and stored at − 20 °C had increased BDNF by 12 months (p =  < 0.0001, Kruskal–Wallis test with Dunn’s post hoc). (B) Plasma isolated by lithium-heparin tubes and stored at − 20 °C had increased BDNF by 12 months (p ≤ 0.0001, Kruskal–Wallis test with Dunn’s post hoc), and had significant inter-month variability. (C) BDNF in plasma isolated from lithium-heparin gel separators increased by 12 months following storage at − 20 °C (p ≤ 0.0001, Kruskal–Wallis test with Dunn’s post hoc), and had significant inter-month variability. (D) Plasma isolated by sodium-heparin tubes had significantly increased BDNF by 12 months, following storage at − 20 °C (p ≤ 0.0001, Kruskal–Wallis test with Dunn’s post hoc), and had significant inter-month variability. (E) When plasma was isolated by glass sodium-heparin tube and stored at − 20 °C, BDNF concentration increased significantly by 12 months (p ≤ 0.0001, Kruskal–Wallis test with Dunn’s post hoc), and had significant inter-month variability. BDNF: brain-derived neurotrophic factor. K2EDTA: potassium EDTA. Li-Hep: lithium heparin. Na-Hep: sodium heparin. *p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001, ****p ≤ 0.0001. Dotted lines indicate the expected range of the means for each plasma separator (calculated to be ± 47.9%, based on inter-assay CV and the mean concentration of BDNF recovered from each plasma separator at Time 0). + : indicates the mean.