The added value of Aβ42/Aβ40 in the CSF signature for routine diagnostics of Alzheimer's disease.

The cerebrospinal fluid (CSF) signature of Alzheimer's disease (AD) includes abnormal levels of amyloid-β 1-42 (Aβ42), total tau (t-Tau) and phosphorylated tau (p-Tau). Several studies have reported that the CSF Aβ42/Aβ40 ratio could outperform CSF Aβ42 as a more accurate marker of brain amyloidosis, since it normalizes the CSF Aβ42 levels according to the total production of Aβ in the brain. In the present study, we wanted to assess the diagnostic utility of adding the Aβ42/Aβ40 ratio within the core AD CSF biomarkers for the classification of patients, according to NIA-AA criteria and Erlangen score. We consecutively recruited 168 patients (62 with AD and 106 with other neurological diseases) who referred to our Memory Clinic for diagnostic work- up from 2003 to 2016. The use of CSF Aβ42/Aβ40 ratio increased the percentage of correctly diagnosed AD patients from 72.0% to 82.8%. The high gain in sensitivity (from 75.8% to 85.5%) was obtained in face of loss of specificity (from 95.3% to 82.5%). Our study showed that the use of CSF Aβ42/Aβ40 could significantly improve the routine diagnostic work up of AD.