Another test for Alzheimers

As StatsChat readers will know, there are lots of candidate tests for Alzheimer’s Disease, all of which are much better than just flipping a coin. These tests may be useful in selecting people for clinical trials, and if we ever get effective disease-modifying treatments, for deciding who to treat. At the moment, though, these tests aren’t much use.

BBC News has another one

Scientists in Japan and Australia have developed a blood test that can detect the build-up of toxic proteins linked to Alzheimer’s disease.

The work, published in the journal Nature, is an important step towards a blood test for dementia.

The test was 90% accurate when trialled on healthy people, those with memory loss and Alzheimer’s patients.

If you’re not paying careful attention, 90% accuracy sounds pretty good. But that’s the accuracy in a group of people where about half of them have Alzheimer’s.  In the population, where most people are ok, the false positive rate will still be scarily high.

Also, in contrast to some tests I’ve written about, the main focus of this paper is differentiating Alzheimer’s Disease from other sorts of dementia

The research paper says

The plasma composite biomarker showed 96.7% sensitivity, 81.0% specificity, and 90.2% accuracy in the overall data (n = 51) when predicting individual Aβ status (Aβ⁺ or Aβ⁻) using the common cut-off value (0.376) (Extended Data Fig. 8e–g). The results suggest that the plasma biomarker could be helpful for the differential diagnosis of AD and aid in determining therapeutic strategies, by providing additional information on the brain Aβ deposition status of individuals.

That’s going to be useful when we get treatments, since the treatments for Alzheimer’s probably won’t work on unrelated kinds of dementia, but it doesn’t really fit with the framing in the story

Alzheimer’s disease starts years before patients have any symptoms of memory loss.

The key to treating the dementia will be getting in early before the permanent loss of brain cells.