Literature Review

Automated measurements of plasma predict amyloid status

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Findings represent significant advances

The investigation by Palmqvist et al. “makes several significant advancements in the field,” said Sid E. O’Bryant, PhD, professor of pharmacology and neuroscience at the University of North Texas Health Science Center in Fort Worth, in an accompanying editorial. The study’s protocol design clears the ground for a context of use of a blood screen for amyloid positivity. Also, the fully automated immunoassay “yields performance measurements that are superior to [those of] many earlier nonautomated procedures,” said Dr. O’Bryant. When Dr. Palmqvist and colleagues applied their discovery findings from a training cohort directly to a test cohort, it produced strong results. “This study suggests that the field is one step closer to the actual application of blood-based biomarkers with specific contexts of use in Alzheimer’s disease.”

The main concern about the plasma biomarkers, however, is the scalability of the methods used to measure them. “If primary care physicians are to use such a technology, the technology must have the capacity to conduct hundreds of millions of assays annually around the globe,” said Dr. O’Bryant. “A blood test for primary care must fit into the existing protocols and parameters in clinical laboratory settings. The blood collection and processing procedures are not applicable to standard clinical lab practice and will cause substantial barriers to clinical application.”

In addition, the study authors emphasize the utility of the immunoassay for primary care, but the study was designed to test for amyloid positivity, which is more appropriate for clinical trials. “No currently available drugs for patient use target amyloid,” said Dr. O’Bryant. “Therefore, this specific context of use is geared more toward clinical trial application than primary care physicians who currently need a test for the presence or absence of Alzheimer’s disease so currently available treatments and support can be put in place for patients and family members.”

Nevertheless, Dr. Palmqvist and associates have presented promising data, Dr. O’Bryant continued. The question in the field is ceasing to be whether blood biomarkers can be used in Alzheimer’s disease, and becoming how they can be used.



Validation cohort was small

Dr. Palmqvist and colleagues acknowledged that a lack of data about APOE was a limitation of their validation analysis. Other limitations that they acknowledged were the small population size, which precluded subpopulation analysis, and the lack of improvement in predictive ability when they replicated the model that included plasma tau.

“Overall, the accuracies of the amyloid-beta 42 and amyloid-beta 40 assays are not sufficient to be used on their own as a clinical test of amyloid-beta positivity,” said Dr. Palmqvist and colleagues. “Additional assay development is needed before this can be recommended, possibly together with other blood biomarkers and screening tools in diagnostic algorithms.”

Even though additional validation studies are necessary, the present findings indicate “the potential usefulness blood assays might have, especially considering the ongoing great need to recruit large cohorts for Alzheimer’s disease drug trials in preclinical and prodromal stages,” the authors concluded.

This investigation was funded by foundations including the European Research Council, the Swedish Research Council, and the Knut and Alice Wallenberg foundation. Several authors are employees of the Roche Group. One author served on a scientific advisory board for Roche Diagnostics, and another received institutional research support from that company.

SOURCE: Palmqvist S et al. JAMA Neurol. 2019 Jun 24. doi: 10.1001/jamaneurol.2019.1632.


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