The New Alzheimer’s Blood Test (p-tau) vs. Amyloid PET Scans: What Patients Should Know

By Dr Soumit Singhai FRCP, Consultant Geriatrician

Why these new Alzheimer’s tests matter

When someone develops memory problems, one of the most important questions is whether Alzheimer’s disease could be the underlying cause.

Until recently, the only way to confirm Alzheimer’s was through specialist brain scans (such as an amyloid PET scan) or invasive spinal fluid tests. Now, a new Alzheimer’s blood test that measures the p-tau protein (phosphorylated tau) is available.

This simple test has raised an important question for patients and families:
Is the blood test enough, or do I still need a brain scan such as an amyloid PET?

The new Alzheimer’s blood test (p-tau protein)

• How it works: This blood test measures levels of phosphorylated tau (p-tau), a protein linked to Alzheimer’s-related changes in the brain.
• Results: Reported on a scale of 0 to 100, giving a probability score:
  • Low score → low probability of Alzheimer’s disease
  • Intermediate score → uncertain, may still need further tests
  • High score → high probability of Alzheimer’s disease
• Advantages for patients:
  • Quick and non-invasive (just a blood sample).
  • More affordable than a brain scan.
  • Useful for detecting early signs of Alzheimer’s.
• Limitations:
  • Provides a probability, not a visual confirmation.
  • Intermediate scores can feel uncertain.
  • Still becoming widely available in clinical practice.

Blood test vs. brain scan: side-by-side comparison

Feature	New Alzheimer’s Blood Test (p-tau protein)	Amyloid PET Scan
Type of test	Blood sample	Brain imaging with tracer
What it shows	Probability score (0–100) for Alzheimer’s	Visual image of amyloid plaques
Result categories	Low / Intermediate / High probability	Positive or Negative (yes/no)
Accuracy	Strongly predictive, especially at high/low ends	Gold standard, highly specific
Advantages	Non-invasive, affordable, quick, widely scalable	Clear visual confirmation, most definitive test
Limitations	Gives probability not certainty, intermediate results may need further tests	More expensive, less available, radiation exposure
Best use	First-line test to screen or triage	Confirmation when blood test is intermediate or absolute certainty required

What this means for patients choosing private memory care

For families exploring private memory care, the choice often comes down to certainty vs. convenience:

• The new Alzheimer’s blood test (p-tau protein test) is simple, affordable, and effective as a first step.
• The amyloid PET scan provides the highest level of certainty, especially when results are unclear or when proof is needed for treatment eligibility.

In practice, many patients begin with the blood test. If the result is clearly low or high, that may be sufficient. If the result is intermediate, or if there is still doubt, an amyloid PET scan is the best next step.

Frequently Asked Questions

What is the new Alzheimer’s blood test?

It is a simple blood test that measures p-tau protein levels, which are linked with changes in the brain caused by Alzheimer’s disease.

How accurate is the p-tau blood test compared to a brain scan?

The p-tau test is very accurate, especially at the low and high ends of the scale. However, in the intermediate range, an amyloid PET scan is often needed for confirmation.

Is the new blood test enough to diagnose Alzheimer’s on its own?

In many cases, yes — especially when the result shows very low or very high probability. But when results are uncertain, an amyloid PET scan gives the most definitive answer.

What are the advantages of the blood test over a PET scan?

It is non-invasive, more affordable, and quick. It provides a good estimate of Alzheimer’s probability without the need for radiation or specialist imaging.

What are the advantages of an amyloid PET scan over the blood test?

A PET scan gives a clear visual yes/no answer about amyloid plaques in the brain, making it the gold standard test when absolute certainty is required.

Which test should I have first?

Most patients start with the new Alzheimer’s blood test. If the result is uncertain or if absolute proof is needed, an amyloid PET scan may then be recommended.