Screening for Alzheimer’s Disease

On March 9, 2014, The-Scientist reported on a new screening test for Alzheimer’s disease.  According to the abstract of the study,

Herein, we describe our lipidomic approach to detecting preclinical Alzheimer’s disease in a group of cognitively normal older adults. We discovered and validated a set of ten lipids from peripheral blood that predicted phenoconversion to either amnestic mild cognitive impairment or Alzheimer’s disease within a 2–3 year timeframe with over 90% accuracy. This biomarker panel, reflecting cell membrane integrity, may be sensitive to early neurodegeneration of preclinical Alzheimer’s disease.

 

Note the 90% accuracy claim of the test.  Now that we have looked at ways to measure a test’s value (i.e. sensitivity, specificity, PPV and NPV), you might wonder what a 90% accuracy means in the context of this study.  Others wondered the same thing and there are a few articles discussing this research finding in the context of medical screenings and being careful about the conclusions one should draw.

  1. Screen the Healthy? – read this page for a quick overview of the issue.
  2. How a “90% accurate” Alzheimer’s test can be wrong 92% of the time – see a good infographic here that visually displays the problem.
  3. On the hazards of significance testing. Part 1: the screening problem – finish by reading this page that shows the issue with screening via probability trees, Baye’s Rule, prevalence affects, and several examples.  An excellent summary of many of the issues we have discussed with screening tests.