Analysis of Combined CSF Biomarkers in AD Diagnosis

Background: The new proposed diagnostic criteria for early diagnosis of Alzheimer's Disease (AD) underline the value of cerebrospinal fluid (CSF) biomarkers. The first aim of the study was to determine the diagnostic accuracy of CSF biomarker A beta(1-42), T-tau, and P-tau in differentiating AD patients in our cohort by means of "pure" biomarkers and in form of a combined analysis of these biomarkers. The second aim of the study was to determine the diagnostic accuracy of these markers for predicting incipient AD in patients with mild cognitive impairment (MCI). Methods: We studied 102 CSF samples: 33 AD [mean age at baseline 71.2 (54 - 86)], 16 MCI [mean age at baseline 71.3 (57 - 78)], 24 non AD dementia, including 7 vascular dementia, 4 frontotemporal degeneration, 5 dementia with Lewy Body, and 8 with other dementia [mean age at baseline 72.7 (51 - 87)] and 32 non-demented neurological patients [mean age at baseline 71.3 (45 - 87) referred to as control (CO) later in the text]. A double sandwich ELISA (Innotest beta amyloid A beta(1-42), hTau and P-tau(181) by Innogenetics, Gent, Belgium) was performed to quantify the concentration of the above biomarkers. The three biomarkers were then combined in the IATI index [(measured Ab1-42)/(240 + 1.18 *measured tau)], and in the ratios A beta(1-42)/T-tau, A beta(1-42)/P-tau, T-tau/A beta(1-42) and P-tau/A beta(1-42). Results: A beta(1-42), T-tau and P-tau(181) concentration showed statistically significant differences between AD and CO (327.2 pg/mL +/- 150.2 pg/mL and 659.4 pg/mL +/- 254.2 pg/mL; 508.2 pg/mL +/- 360.2 pg/mL and 305.3 pg/mL +/- 228.9 pg/mL; 82.2 pg/mL +/- 26.1 pg/mL and 45.3 pg/mL +/- 26.4 pg/mL, respectively, p < 0.05), while the difference between AD and MCI was statistically different only for A beta(1-42) (327.2 pg/mL +/- 150.2 pg/mL and 600.8 +/- 271.9 pg/mL, respectively, p < 0.05). The IATI index was 0.5 +/- 0.3 in AD, 0.9 +/- 0.6 in MCI, 1.37 +/- 0.9 in non AD dementia and 1.26 +/- 0.8 in non-demented neurological patients. With a cut-off fixed at 1 the sensitivity and specificity of the IATI index in discriminating AD from CO was 84% and 52%, respectively. Conclusions: This study confirms the great significance of CSF biomarker measurements in AD diagnosis in clinical routine. It is understood that a clinical diagnostic work-up is necessary in the process. Moreover, a biochemical profile of CSF biomarkers requires further investigations.