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,  < .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,  < .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.