Investigators Tout New Alzheimer Disease Blood Immunoassay Test

Tharick A. Pascoal, MD

This article, "Plasma P-Tau181 Biomarker May Be Accessible, Scalable Test for Alzheimer Disease," was originally published in NeurologyLive.

New research points to blood immunoassay as a predictor of tau and amyloid-ß pathologies, helping to identify potential cases of Alzheimer disease earlier.

Analysis of data from a number of cohorts suggests that the validated an ultrasensitive blood immunoassay for cerebrospinal fluid (CSF) tau phosphorylated at threonine 181 (p-tau181) can predict both tau and amyloid-ß pathologies, differentiate Alzheimer disease from other disorders, and identify it across the clinical spectrum.

A team, led by Tharick A. Pascoal, MD, Translational Neuroimaging Laboratory, The McGill University Research Centre for Studies in Aging, examined 37 individuals from the discovery cohort, 226 from the first validation cohort (dubbed TRIAD), 763 in the second validation cohort (dubbed BioFINDER-2), and 105 in the primary care cohort, totaling 1131 individuals.

The discovery cohort included cognitively unimpaired older adults (n = 18) and those with Alzheimer (n = 19), while the primary care cohort included young adults (n = 11), cognitively unimpaired older adults (n = 72), those with MCI (n = 12), and those with Alzheimer (n = 10).

TRIAD also included young adults (n = 27), cognitively unimpaired older adults (n = 113), and those with MCI (n = 45), Alzheimer’s disease (n=33), and FTD (n = 8).

The BioFINDER-2 cohort included cognitively unimpaired older adults (n = 337), those with MCI (n = 191) and Alzheimer (n = 126), those with behavioral variant FTD or primary progressive aphasia (PPA; n = 18), Parkinson or multiple system atrophy (n = 36), vascular dementia (n = 12), and PSP or CBS (n = 21).

The researchers noted that the blood biomarker could serve as a simple, accessible, and easily scalable test for the screening and diagnosis of Alzheimer.

The findings showed that plasma p-tau181 gradually increased along the Alzheimer continuum, with the lowest concentrations observed in amyloid β-negative young adults and cognitively unimpaired older adults, higher concentrations shown in the amyloid β-positive cognitively unimpaired older adults and mild cognitive impairment (MCI) groups.

The investigators also found the highest concentrations reported in the amyloid β-positive MCI and Alzheimer disease groups (P <.001 for Alzheimer vs all other groups).

“CSF and PET biomarkers of amyloid β and tau accurately detect Alzheimer's disease pathology, but the invasiveness, high cost, and poor availability of these detection methods restrict their widespread use as clinical diagnostic tools,” the authors wrote “CSF p-tau181 is a highly specific biomarker for Alzheimer's disease pathology. We aimed to assess whether blood p-tau181 could be used as a biomarker for Alzheimer's disease and for prediction of cognitive decline and hippocampal atrophy.”

Plasma p-tau181 distinguished Alzheimer disease dementia from young adults who were amyloid β-negative (area under the curve [AUC], 99.40%) and cognitively unimpaired older adults (AUC, 90.21—98.24% across cohorts).

Additionally, it differentiated from other neurodegenerative disorders, including frontotemporal dementia (FTD; AUC, 82.76—100% across cohorts), vascular dementia (AUC, 92.13%), progressive supranuclear palsy (PSP) or corticobasal syndrome (CBS; AUC, 88.47%), and Parkinson's disease or multiple system atrophy (MSA; AUC, 81.90%).

Additionally, the biomarker was linked with positron emission tomography (PET) measured cerebral tau (AUC, 83.08—93.11% across cohorts) as well as amyloid β (AUC, 76.14–88.09% across cohorts) pathologies.

It was also associated with 12-month cognitive decline (P = .0015) and hippocampal atrophy (P = .015).

In the primary care cohort, plasma p-tau181 was able to distinguish Alzheimer disease from young adults (AUC, 100%) and cognitively unimpaired older adults (AUC, 84.44%), though it did not distinguish from MCI (AUC, 55.00%).

“The blood p-tau181 test showed high accuracy for predicting in-vivo tau tangles and a predictive power to detect amyloid β plaque-positive individuals that was similar to high-performance mass spectrometry-based amyloid β plasma assays,” the authors wrote, noting that blood p-tau181 can identify those with brain tau and amyloid β pathology with an AUC of up to 90%.

“The strong correlation between plasma p-tau181 and amyloid β PET, together with the increased plasma p-tau181 in amyloid β PET-positive and tau PET-negative (Braak 0) individuals suggests that this new test detects Alzheimer disease type pathology in the very early disease stages,” they wrote.

The technology has applications for diagnosis and recruitment for disease-modifying trials. The blood p-tau181 assay has the potential to be incorporated into clinical practice as a rapid screening test to rule out Alzheimer’s disease pathophysiology and to guide therapy and clinical management of patients with dementia.

The study, “Blood phosphorylated tau 181 as a biomarker for Alzheimer's disease: a diagnostic performance and prediction modelling study using data from four prospective cohorts,” was published online in The Lancet Neurology.