PrecivityAD test has guided clinical decision-making

Doctors rely on the blood test when considering Alzheimer's treatment, study shows

Lindsey Shapiro, PhD avatar

by Lindsey Shapiro, PhD |

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The PrecivityAD blood test from C2N Diagnostics significantly influences clinicians’ decisions about whether to treat people with cognitive impairments for Alzheimer’s disease.

C2N, which sponsored the recent study, believes those findings offer robust real-world evidence that blood biomarker testing in the clinic helps to guide treatment decisions and improve patient care.

PrecivityAD, which measures certain Alzheimer’s biomarkers, already is available in clinics in 49 U.S. states, the District of Columbia, and Puerto Rico to help doctors diagnose the neurodegenerative disease.

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“These data address a major gap in the further use of blood biomarkers in the real world, patient care setting,” Joel B. Braunstein, MD, CEO of C2N, said in a press release.

Braunstein noted that the findings “complement the previously published work on clinical validity and test performance of the PrecivityAD blood test.”

The study, “A blood biomarker test for brain amyloid impacts the clinical evaluation of cognitive impairment,” was published in the Annals of Clinical and Translational Neurology.

Buildup of toxic clumps, or plaques, of the amyloid beta protein in the brain is a hallmark of Alzheimer’s. Identification of these plaques using brain positron emission tomography (PET) scans is used to diagnose the disease and differentiate it from other causes of cognitive decline.

Still, existing studies estimate that Alzheimer’s is misdiagnosed at a rate of about 30-50%. While PET scans and analyses of the fluid that surrounds the brain and spinal cord increase diagnostic accuracy, these tests are not as easily implemented in routine clinical care and may not be accessible for all patients.

PrecivityAD is a blood test designed to predict the likelihood that a person, aged 60 or older, with cognitive dysfunction will be amyloid-positive on a PET scan, helping to bypass the need for more expensive, invasive, or complicated diagnostic techniques.

PrecivityAD measures two forms of amyloid beta

It measures the ratio of two forms of amyloid beta — amyloid beta 40 and 42 — in addition to determining which type of the apolipoprotein E (ApoE) is present in a person’s blood. Certain mutations in the gene encoding ApoE are associated with the production of an abnormal protein that’s strongly linked to Alzheimer’s risk.

Based on PrecivityAD test results, as well as a person’s age, an Amyloid Probability Score (APS) on a scale of 0-100 is generated, with higher scores indicating a greater likelihood of being amyloid-positive on a PET scan, and subsequently develop Alzheimer’s.

Clinical validation studies have shown that the test’s APS predicted, with more than 80% accuracy, which of 686 cognitively impaired adults were amyloid-positive on a PET scan. This and other studies in both cognitively normal and cognitively impaired adults suggest that the PrecivityAD test may help clinicians in Alzheimer’s diagnosis.

However, real-world evidence regarding its impacts on clinical decision-making were lacking.

That’s why C2N launched a study called the Quality Improvement PrecivityAD Clinician Survey (NCT05477056), whose findings were now published.

Specialists in 15 states surveyed

Neurologists or other cognitive specialists across 15 different U.S. sites were educated on the intended use of PrecivityAD and the resulting APS, and were asked to complete online surveys after administering the test to their patients.

Ultimately, the analysis included data from 347 patients, 56% of whom were women, with a median age of 75. These patients, who met PrecivityAD test’s intended use criteria, corresponded to 95% of all patients selected by clinicians to undergo the test.

A total of 133 patients (38%) were considered to have a low APS and therefore, a low likelihood of Alzheimer’s, whereas 162 (47%) had a high APS and were considered more likely to have the disease. The remaining 52 patients (15%) had an intermediate APS.

Prior to the PrecivityAD test, clinicians had rated patients in the low APS group as having an average 58% chance of developing Alzheimer’s, which was significantly reduced to 23% after seeing the test results. Likewise, the mean Alzheimer’s probability in the intermediate group dropped significantly from 64% to 52%.

On the other hand, the clinician-rated likelihood of Alzheimer’s was increased significantly from a mean of 71% pre-test to 89% post-test for those in the high APS group.

This shift influenced which patients the doctors were likely to prescribe Alzheimer’s therapies.

Particularly, the use of these medications was decreased significantly by 46% in the low APS group, because they weren’t considered likely to have the amyloid deposition that marks the disease. Correspondingly, Alzheimer’s medications were increased significantly by 57% in the high APS group.

“Among the 347 patients, 85% (295/347) had clinically useful Low or High APS results,” the researchers wrote, adding that participating clinicians “reported value in APS results in both the Low APS and High APS categories.”

“This study is among the first to show clinical management changes by cognitive specialists using a [blood biomarker] test assessing the presence or absence of brain amyloid among … patients being evaluated for AD or other causes of cognitive decline,” the team wrote.

Blood-based tests gain credibility, popularity

The recent findings add to a growing body of evidence that blood-based tests like PrecivityAD can help to boost diagnostic accuracy while minimizing the need for less feasible tests.

“Larger trials with longer follow-up are warranted to further explore the effect of the PrecivityAD blood test results on changes in diagnostic and management strategies as well as patient outcomes,” the researchers wrote.