Effects of pre‐analytical procedures on blood biomarkers for Alzheimer's pathophysiology, glial activation, and neurodegeneration

INTRODUCTION: We tested how tube types (ethylenediaminetetraacetic acid [EDTA], serum, lithium heparin [LiHep], and citrate) and freeze–thaw cycles affect levels of blood biomarkers for Alzheimer's disease (AD) pathophysiology, glial activation, and neuronal injury. METHODS: Amyloid beta (Aβ)42, Aβ40, phosphorylated tau181 (p‐tau181), glial fibrillary acidic protein, total tau (t‐tau), neurofilament light, and phosphorylated neurofilament heavy protein were measured using single molecule arrays. RESULTS: LiHep demonstrated the highest mean value for all biomarkers. Tube types were highly correlated for most biomarkers (r > 0.95) but gave significantly different absolute concentrations. Weaker correlations between tube types were found for Aβ42/40 (r = 0.63–0.86) and serum t‐tau (r = 0.46–0.64). Freeze–thaw cycles highly influenced levels of serum Aβ and t‐tau (P < .0001), and minor decreases in EDTA Aβ40 and EDTA p‐tau181 were found after freeze–thaw cycle 4 (P < .05). DISCUSSION: The same tube type should be used in research studies on blood biomarkers. Individual concentration cut‐offs are needed for each tube type in all tested biomarkers despite being highly correlated. Serum should be avoided for Aβ42, Aβ40, and t‐tau. Freeze–thaw cycles > 3 should be avoided for p‐tau181.