Disclosing plasma p-tau217 early raised diagnostic certainty tenfold without adding distress

Design

Prospective single-centre randomised clinical trial

Population

220 new memory clinic outpatients with SCD, MCI or mild dementia in Spain

Primary outcome

Very high-confidence etiological diagnosis (≥90%) at 3 months

Effect

50.0% with early disclosure vs 4.6% with delayed disclosure (P<0.001)

A randomised trial at a single memory clinic in Spain enrolled 220 consecutive new outpatients with subjective cognitive decline, mild cognitive impairment or mild dementia and no etiological diagnosis. Plasma p-tau217 and neurofilament light results were disclosed to the neurologist and patient at three months or, in the control arm, at nine months.

At three months, a very high-confidence etiological diagnosis was reached in 50.0% with early disclosure against 4.6% with delayed disclosure. Early disclosure was linked to more starts of symptomatic Alzheimer treatment (14.3% vs 4.6%), fewer repeat neuropsychological assessments planned for diagnostic clarification (30.4% vs 52.8%), and more discharges to primary care (31.3% vs 12.0%). Anxiety, depression, stress and quality of life did not worsen.

Certainty converged once both arms had their results, except in mild cognitive impairment, where the early-disclosure arm stayed more certain. That is the group where a blood test may matter most.

The trial was at one specialist centre with a well-characterised population. Blood biomarkers perform less well in primary care, in kidney disease and in very old patients, and access in India remains limited and costly.

• Consider plasma p-tau217 in specialist memory clinic work-up of mild cognitive impairment to firm up the cause
• Interpret results alongside clinical assessment; blood biomarkers are less reliable in chronic kidney disease
• Discuss what a positive or negative result would change before ordering it
• A clear diagnosis can allow earlier discharge to primary care with a plan
• Patients in this trial did not show more distress after early disclosure

Why it matters

It shows a blood test can shorten months of diagnostic uncertainty in mild cognitive impairment.

Don't overread it

Higher diagnostic confidence is not the same as better patient outcomes, and the trial was at a single specialist centre.

The statistics, in plain English

50% versus 4.6% is a very large difference, but it measures clinician confidence, not whether diagnoses were correct or patients did better. The treatment and discharge differences have confidence intervals clear of zero.

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