Alzheimer's disease (AD), a condition marked by cognitive decline and the presence of beta-amyloid (Aβ) plaques and neurofibrillary tangles in the brain, poses diagnostic challenges. Amyloid positron emission tomography (PET) imaging is a well-established diagnostic aid for AD but comes with high costs, invasiveness, and the need for specialist equipment, unlike blood tests. Now, new study findings have revealed that a novel amyloid blood test could reduce reliance on PET imaging for some patients experiencing mild cognitive issues to enable therapeutic focus on non-AD causes, thus expanding access to quality evaluation and reducing healthcare costs.

In what is considered one of the largest published studies, researchers evaluated the efficacy of amyloid blood testing in diagnosing AD. The study utilized 6,192 anonymized lab results from patients who were administered Quest Diagnostics’ (Secaucus, NJ, USA) AD-Detect Beta-amyloid ratio test AΒ42/40. This test measures the ratio of amyloid beta 42 and 40 proteins (Aβ42/40) found in the brain and also circulating in the bloodstream. The clinical accuracy of the Quest test was verified against 250 samples from individuals who also had amyloid PET scans and demographic data. Additionally, the study examined the blood test's performance across various interpretative ranges based on different cutoffs, or amyloid levels in the blood.

Findings from the study suggest that the Quest test, which analyzes amyloid protein levels using highly sensitive mass spectrometry, could effectively indicate when AD is unlikely to be the cause of a patient's mild cognitive impairment. The analysis showed that up to 99% of patients who tested negative for amyloid proteins in the brain via PET imaging would likely also test negative using the Quest blood test. This predictive capability could lead to a 40% reduction in the need for PET brain scans, offering significant potential healthcare cost savings for these patients.

"These findings show Aβ42/40 testing is very helpful in identifying amyloid pathology in populations with a high prevalence of AD, particularly older individuals," said Michael Racke, MD, Medical Director of Neurology at Quest Diagnostics. "We believe the comparatively low specificity reflects the limits of PET scans to identify the earliest stages of AD pathology and that many of these patients will progress to be PET-positive as the disease worsens."

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