Scientists have developed a "clock" model based on a single blood test that estimates when cognitively intact individuals are likely to develop Alzheimer's symptoms[1]. The model relies on the biomarker p-tau217 and the amyloid ratio[1]. Blood levels of p-tau217 are significantly higher in Alzheimer's disease - more than 8 times higher in the dementia stage than in elderly people without the disease[1]. The p-tau217 test is up to 96% more accurate in identifying elevated beta-amyloid levels and up to 97% more accurate in identifying tau[1][5]. The combination of p-tau217 with an amyloid ratio of 42/40 produces an amyloid probability score that is most predictive[1]. The p-tau217 test is specific for Alzheimer's disease with a diagnostic accuracy of 89-98% and better than MRI, comparable to PET scan[1][2][3]. In patients with Alzheimer's disease, the levels of p-tau217 are approximately 7 times higher than in healthy subjects[3].