Elevation of plasma phosphorylated tau181 during neurological illnesses affecting consciousness and kidney dysfunction

INTRODUCTION: Phosphorylated tau (p‐tau)181 has become a promising blood‐based Alzheimer's disease (AD) biomarker. We studied the agreement of plasma p‐tau181 and cerebrospinal fluid (CSF) markers in patients with alteration of consciousness (AOC). METHODS: Plasma and CSF were simultaneously collected in participants presenting with AOC. Plasma p‐tau181 was measured using the single‐molecule array. CSF biomarkers were classified according to the amyloid/tau/neurodegeneration (AT[N]) framework. RESULTS: Among participants enrolled, the median (interquartile range) age was 57 (28.5–75) years and 5.8% had AD. Plasma p‐tau181 yielded area under the curve of 0.85 and showed moderate correlation with CSF p‐tau181 (Rho = 0.42, P < .001). Using the historical cut‐point, many non‐AD participants had elevated plasma p‐tau181 resulting in a specificity of 0.57. Plasma p‐tau181 correlated with the glomerular filtration rate (Rho = –0.52, P < .001). Among A− participants with elevated plasma p‐tau181, 42% had kidney dysfunction. DISCUSSION: Plasma p‐tau181 showed inadequate specificity in patients with AOC partially attributable to concomitant kidney dysfunction.