A New Alzheimer’s Blood Test: A Diagnostic Breakthrough

For decades, the path to a definitive Alzheimer’s disease (AD) diagnosis has been challenging, relying on a combination of cognitive testing, expensive PET scans, or invasive lumbar punctures. A reliable and accessible blood test has long been a primary goal for the field, promising to significantly improve the diagnostic process for both patients and clinicians.

A landmark new study from researchers at the Mayo Clinic, published in Alzheimer’s & Dementia, shows that this goal is moving firmly into clinical reality. Their work validates a powerful new blood test using plasma-based biomarkers — marking a significant step forward for both clinical and legal communities.

The Breakthrough: A Blood Test with Near-CSF Accuracy

Critically, the study evaluated the performance of plasma biomarkers in a real-world setting — a cohort of over 500 patients from an outpatient memory clinic. This population reflects the true complexity of cognitive assessment: multiple health issues, variable presentations, and diagnostic uncertainty.

The biomarker at the centre of the study is phosphorylated tau 217 (p-tau217), a protein closely associated with Alzheimer’s pathology.

Key findings include:

• High Sensitivity (95%): Accurately identified patients with Alzheimer’s.
• High Specificity (82%): Effectively ruled out those without the disease.
• Strong Overall Accuracy (AUC 0.91): Comparable to cerebrospinal fluid (CSF) tests, long considered the gold standard.

Notably, the researchers demonstrated that a “two-cutpoint” model allowed 86% of patients to receive a definitive positive or negative result based on a single blood test — substantially streamlining the diagnostic process.

Important Consideration: The Role of Kidney Function

The study also noted that p-tau217 levels in plasma can be influenced by renal function. Specifically, patients with reduced kidney function (as measured by eGFR) exhibited higher levels of p-tau217, independent of Alzheimer’s diagnosis. This is due to the kidneys’ role in protein clearance — reduced renal filtration can lead to protein accumulation in the bloodstream.

While this does not negate the utility of the biomarker, it underscores the importance of interpreting results alongside renal function data to maintain diagnostic accuracy.

Medico-Legal Relevance

As blood-based biomarkers like p-tau217 enter clinical use, they will inevitably influence medico-legal assessments. Whether in claims concerning cognitive impairment, testamentary capacity, or questions of delayed diagnosis, this tool will become increasingly relevant.

For experts and solicitors alike, an awareness of both the strengths and caveats of these tools will be essential as standards of care evolve.

0121 485 6000

contact@gyrusgroup.com