Combined CSF tau, p-tau181 and amyloid-beta 38/40/42 for diagnosing Alzheimer's disease

Cerebrospinal fluid (CSF) concentrations of amyloid-beta (A beta) 1-38, 1-40, 1-42, total-tau and phospho-tau in samples from 156 patients with Alzheimer's disease (AD) (n = 44), depressive cognitive complainers (DCC, n = 25) and various other forms of non-Alzheimer dementias (NAD, n = 87) were analyzed by electrochemiluminescence and enzyme linked immunosorbent assay, respectively. A significant decrease of CSF A beta 1-42 was the most powerful single marker for differentiation of AD from DCC, yielding accuracies of beyond 85%. Increased p-tau and the ratio A beta 1-42/A beta 1-38 yielded accuracies of beyond 80 and 85%, respectively, to discriminate AD versus NAD. Combining p-tau with A beta 1-42/A beta 1-38 resulted in a sensitivity of 94% for detection of AD and 85% specificity for excluding NAD. Decreased CSF A beta 1-42 represents a core biomarker for AD. The lack of specificity for exclusion of NAD can be most effectively compensated by the ratio A beta 1-42/A beta 1-38. The ratio A beta 1-42/A beta 1-38/p-tau powerfully discriminates AD versus NAD and fulfils the accuracy requirements for an applicable screening and differential diagnostic AD biomarker.