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Cognitact PlasmarkAD Alzheimer's Blood Test Shows Promise as Alzheimer's Dx Tool


NEW YORK – A team led by researchers at the Hong Kong University of Science and Technology (HKUST) has developed a plasma proteomics-based test for aiding the diagnosis of Alzheimer's disease.

The test, which measures the levels of 21 proteins in patient blood samples using Olink's proximity extension assay, has been licensed to Chinese diagnostics firm Cognitact, which currently offers the test in Hong Kong under the name PlasmarkAD and is looking to expand into mainland China and other countries, said Nancy Ip, director of the State Key Laboratory of Molecular Neuroscience at HKUST and one of the test's inventors. The test sells for around HK$7,000 (US$895).

In a study published this month in Alzheimer's & Dementia, Ip and her coauthors detailed the test's performance compared to existing Alzheimer's biomarkers including plasma amyloid beta 42/40 ratio, phosphorylated-tau 181 (p-tau 181), and neurofilament light chain (NfL), evaluating it in three cohorts comprising a total of 1,264 individuals.

The first cohort consisted of 1,000 Hong Kong Chinese subjects, of whom 317 were cognitively normal, 190 were with mild cognitive impairment (MCI), and 493 were with Alzheimer's disease. These patients had been evaluated via clinical examination, the Montreal Cognitive Assessment test, MRI, and measurement of plasma Aβ42/40 ratio, p-tau 181, and NfL using Quanterix's Neurology 4-Plex E Advantage assay and P-Tau 181 Advantage V2 assay.

The second cohort consisted of 47 Hong Kong Chinese subjects who underwent the same evaluation as the first cohort plus Aβ-PET. Of these subjects, nine were cognitively normal and negative for brain amyloid, 13 had MCI and were positive for brain amyloid, and 25 had Alzheimer's and were positive for brain amyloid.

The third cohort consisted of 217 individuals from the Spanish BIODEGMAR cohort, of whom 20 were cognitively normal and amyloid negative, 68 had MCI and were amyloid positive, and 129 had Alzheimer's and were amyloid positive. In addition to blood testing, clinical evaluation, and MRI, these subjects had cerebrospinal fluid collected for testing of CSF Aβ42/40 ratio and total tau using Fujirebio's Lumipulse G60011 assay.

In the first cohort, the PlasmarkAD test distinguished between cognitively normal subjects and those with Alzheimer's with an area under the curve of 0.97. Plasma p-tau 181 also performed with an AUC of 0.97 in this cohort, while NfL had an AUC of 0.92, and Aβ42/40 ratio had an AUC of 0.67. The PlasmarkAD test showed substantially higher performance than the other measures for distinguishing between subjects with MCI and those with Alzheimer's, with an AUC of 0.87 compared to 0.78 for NfL, 0.65 for p-tau 181, and 0.53 for Aβ42/40 ratio.

In the second Hong Kong cohort, the PlasmarkAD test distinguished cognitively normal, amyloid-negative subjects from subjects with Alzheimer's with an AUC of 0.99 and from subjects with MCI with an AUC of 0.89, in both cases outperforming plasma Aβ42/40 ratio, p-tau 181, and NfL.

In the Spanish cohort, the test distinguished cognitively normal, amyloid-negative subjects from subjects with Alzheimer's with an AUC of 0.94 and from subjects with MCI with an AUC of 0.84, indicating, the authors noted, the generalizability of the assay to a population of European descent.

The study did not include data comparing PlasmarkAD to p-tau 217, which has emerged as perhaps the most powerful plasma marker for identifying the presence of brain amyloid pathology in individuals suspected of having Alzheimer's disease.

Ip said that the researchers' "in-house data suggest that the 21-protein panel performs similarly to plasma p-tau 217 in detecting individuals [with MCI] with abnormal amyloid pathology."

Given equivalent performance, p-tau 217 enjoys the advantage of simplicity as a single-analyte assay. Ip suggested, however, that the larger size of the PlasmarkAD panel could provide useful insights into different parts of the Alzheimer's disease process.

"Our panel can simultaneously assess the activities of five biological processes crucial in AD, including neurodegeneration, innate immunity, inflammation, vascular functions, [and] metabolic activities," she said.

She added that use of markers covering a variety of biological processes could aid research into different subtypes of the disease and the various mechanisms underlying its development, which could "open the door for interventions other than anti-amyloid therapy."

Currently, the test is intended to aid diagnosis of Alzheimer's and MCI, Ip said. She added that she and her colleagues are now researching whether it might be useful for monitoring disease progression, which she noted could position it for uses including stratifying patients and guiding treatment with therapies like anti-amyloid drugs.

Recent US Food and Drug Administration approvals of anti-amyloid drugs — in particular of Eisai's Alzheimer's drug Leqembi (lecanemab) — have further accelerated interest in blood-based Alzheimer's tests as such assays could offer tools to evaluate individuals for anti-amyloid therapy that are less expensive and less invasive than the existing gold standards of PET and CSF-based testing.

Companies including C2N Diagnostics, Quest Diagnostics, Quanterix, and Alzpath currently offer laboratory-developed blood tests to aid in diagnosing individuals with Alzheimer's. This week, Laboratory Corporation of America announced that it has launched a test for plasma p-tau 217, complementing its existing portfolio of Alzheimer plasma markers which includes Aβ42/40 ratio, p-tau 181, and NfL.

At last year's Alzheimer's Association International Conference in Amsterdam, a working group brought together by the Alzheimer's Association and the US National Institutes of Health's National Institute on Aging (NIA) proposed that blood-based markers be included in clinical guidelines for Alzheimer's testing.

As the push for plasma-based Alzheimer's testing has grown, however, some have raised concerns that the accessibility of such tests will lead to their use in patient populations where the utility of testing and benefits of anti-amyloid treatment remain unproven. Last year, Quest Diagnostics began offering its AD-Detect Alzheimer's blood test as a consumer-initiated product, drawing criticism from a number of researchers and clinicians in the Alzheimer's space who said that the company's criteria for ordering the test were too lax and would likely generate large numbers of false positives that could add to patient backlogs at already overburdened memory clinics.

After initially making the test available to asymptomatic individuals, Quest backtracked on that decision and required that people ordering the test certify that they were experiencing mild cognitive impairment or decline and at least one additional risk factor. The company stopped offering the consumer-initiated test at the end of 2023.