Nathalie Le Bastard

Standardization of preanalytical aspects of cerebrospinal fluid biomarker testing for Alzheimer's disease diagnosis: A consensus paper from the Alzheimer's Biomarkers Standardization Initiative

Numerous studies show that the cerebrospinal fluid biomarkers total tau (T‐tau), tau phosphorylated at threonine 181 (P‐tau181P), and amyloid‐β (1‐42) (Aβ1–42) have high diagnostic accuracy for Alzheimers disease. Variability in concentrations for Aβ1–42, T‐tau, and P‐tau181P drives the need for standardization.

Recommendations to standardize preanalytical confounding factors in Alzheimer's and Parkinson's disease cerebrospinal fluid biomarkers: an update

Early diagnosis of neurodegenerative disorders such as Alzheimers (AD) or Parkinsons disease (PD) is needed to slow down or halt the disease at the earliest stage. Cerebrospinal fluid (CSF) biomarkers can be a good tool for early diagnosis. However, their use in clinical practice is challenging due to the high variability found between centers in the concentrations of both AD CSF biomarkers (Aβ42, total tau and phosphorylated tau) and PD CSF biomarker (α-synuclein). Such a variability has been partially attributed to different preanalytical procedures between laboratories, thus highlighting the need to establish standardized operating procedures. Here, we merge two previous consensus guidelines for preanalytical confounding factors in order to achieve one exhaustive guideline updated with new evidence for Aβ42, total tau and phosphorylated tau, and α-synuclein. The proposed standardized operating procedures are applicable not only to novel CSF biomarkers in AD and PD, but also to biomarkers for other neurodegenerative disorders.

Improved discrimination of autopsy-confirmed Alzheimer's disease (AD) from non-AD dementias using CSF P-tau181P

To establish diagnostic accuracy (acc) and optimal cut-off levels of CSF tau phosphorylated at threonine 181 (P-tau(181P)) for discriminating Alzheimers disease (AD) from non-AD dementias in autopsy-confirmed dementia patients, CSF levels of beta-amyloid peptide (Abeta(1-42)), total tau protein (T-tau) and P-tau(181P) from patients with definite AD (n=95) and non-AD dementias (n=50) were determined with single-parameter ELISA kits. Optimal P-tau(181P) cut-off levels for differentiating AD from pooled non-AD dementias, dementia with Lewy bodies (DLB) and frontotemporal dementia (FTD) were 50.4pg/mL (acc=0.73), 52.8pg/mL (acc=0.73) and 35.3pg/mL (acc=0.90), respectively. The optimal CSF P-tau(181P) cut-off level for discriminating AD from non-AD dementias was 50.4pg/mL. Optimal CSF P-tau(181P) cut-off levels differed between non-AD diagnostic dementia categories.

Is the geriatric depression scale a reliable screening tool for depressive symptoms in elderly patients with cognitive impairment

To determine the reliability of the 30‐item Geriatric Depression Scale (GDS‐30) for the screening of depressive symptoms in dementia and mild cognitive impairment (MCI) using the Cornell Scale for Depression in Dementia (CSDD) as the ‘gold standard’.

Added diagnostic value of CSF biomarkers in differential dementia diagnosis

This study aimed to investigate whether cerebrospinal fluid (CSF) biomarkers could have helped the clinician in differential dementia diagnosis in case of clinically ambiguous diagnoses, as compared to autopsy-confirmed dementia diagnosis as gold standard. Twenty-two patients of our autopsy-confirmed dementia population totalling 157 patients had an ambiguous clinical diagnosis at CSF sampling and were included in statistical analysis. CSF levels of β-amyloid peptide (Aβ(1-42)), total tau protein (T-tau) and tau phosphorylated at threonine 181 (P-tau(181P)) were determined. A biomarker-based model was applied to discriminate between AD and NON-AD dementias. AD and NON-AD patients showed no significant differences in Aβ(1-42) and T-tau concentrations, whereas P-tau(181P) concentrations were significantly higher in AD compared to NON-AD patients. The biomarker-based diagnostic model correctly classified 18 of 22 (82%) patients with clinically ambiguous diagnoses. Using a biomarker-based model in patients with clinically ambiguous diagnoses, a correct diagnosis would have been established in the majority of autopsy-confirmed AD and NON-AD cases, indicating that biomarkers have an added diagnostic value in cases with ambiguous clinical diagnoses.

No correlation between time-linked plasma and CSF Aβ levels

Plasma beta-amyloid protein (Abeta) isoforms are considered potential biomarkers for Alzheimers disease (AD) and dementia. The relation between plasma and cerebrospinal fluid (CSF) levels of Abeta isoforms remains unclear. In order to identify possible correlations between Abeta levels in plasma and CSF we determined Abeta levels in time-linked plasma and CSF samples. Abeta concentrations in plasma (Abeta(1-42) and Abeta(N-42)) and CSF (Abeta(1-42)) samples from 49 AD patients, 47 non-Alzheimers disease dementia (NONAD) patients, 39 MCI patients and 29 controls were determined using a multi-parameter fluorimetric bead-based immunoassay using xMAP((R)) technology (for plasma) and a conventional single-parameter ELISA (for CSF). Plasma Abeta(1-42) concentrations did not correlate with CSF Abeta(1-42) concentrations in the total study population, or in the different diagnostic groups. No correlations between plasma Abeta(N-42) and CSF Abeta(1-42) levels were found either. The CSF/serum albumin index did not show any significant differences between AD, NONAD, MCI and controls. These results suggest that the Abeta levels in plasma are independent of the Abeta levels in CSF both in dementia and controls. The fact that CSF and plasma Abeta do not correlate in patients as well as controls and no significant differences in plasma Abeta(1-42) or Abeta(N-42) between patients and controls can be detected hampers the diagnostic utility of the plasma Abeta levels as biomarkers for dementia.

Importance and Impact of Preanalytical Variables on Alzheimer Disease Biomarker Concentrations in Cerebrospinal Fluid

BACKGROUND Analyses of cerebrospinal fluid (CSF) biomarkers (β-amyloid protein, total tau protein, and hyperphosphorylated tau protein) are part of the diagnostic criteria of Alzheimer disease. Different preanalytical sample procedures contribute to variability of CSF biomarker concentrations, hampering between-laboratory comparisons. The aim of this study was to explore the influence of fractionated sampling, centrifugation, freezing temperature, freezing delay, and freeze-thaw cycles on CSF biomarker analyses. METHODS We studied fractionated sampling in sequential aliquots of lumbar CSF. Centrifuged and noncentrifuged samples from the same fraction were compared. CSF samples were subjected to different protocols (liquid nitrogen, -80 °C, and -20 °C; 24 h at 2-8 °C; and 24 and 48 h at room temperature). To study the influence of freeze-thaw cycles, samples were thawed up to 4 times and refrozen at -80 °C. CSF was collected in polypropylene tubes. We measured CSF biomarker concentrations with commercially available single-analyte Innotest assays. RESULTS CSF biomarker concentrations from non-blood-contaminated samples are not influenced by centrifugation or fractionated sampling. Freezing temperature and delayed storage can affect biomarker concentrations; freezing of CSF samples at -80 °C as soon as possible after collection is recommended. Consecutive freezing and thawing of CSF samples up to 3 times had little effect. CONCLUSIONS Temperature of freezing, delay until freezing, and freeze-thaw cycles significantly influence CSF biomarker concentrations, stressing the need for standard operating procedures for preanalytical sample handling. The differences observed in this study are, however, relatively small, and the impact on the clinical value of these CSF biomarkers needs to be determined.

Cerebrospinal Fluid Aβ1-40 Improves Differential Dementia Diagnosis in Patients with Intermediate P-tau181P Levels

It is assumed that the concentration of amyloid-β1-40 (Aβ1-40) in cerebrospinal fluid (CSF) reflects the total amount of Aβ protein in the brain and thus allows a better interpretation of inter-individual differences in Aβ quantity than the Aβ1-42 concentration. In this study, Aβ1-40 was added to the existing CSF biomarker panel of Aβ1-42, total tau (T-tau), and phosphorylated tau (P-tau181P) in order to test whether the accuracy of the differential dementia diagnosis improved. The concentration of Aβ1-40 (INNOTEST® β-amyloid(1-40) prototype version, Innogenetics NV, Belgium) and the other biomarkers (INNOTEST®) was determined in CSF samples from 80 Alzheimers disease (AD) patients, 75 non-AD dementia patients, and 30 controls. A large proportion of the study population had autopsy-confirmed neurodegeneration (AD: 73/80 = 91%; non-AD: 38/75 = 51%). The levels of Aβ1-40 were decreased in AD (10856 ± 4745 pg/mL) and non-AD patients (10519 ± 4491 pg/mL) when compared to controls (14760 ± 7846 pg/mL) (p = 0.002 and p = 0.001). The Aβ1-42/Aβ1-40 ratio was significantly decreased in AD (0.043 ± 0.021) as compared to non-AD patients (0.064 ± 0.027; p < 0.001) and controls (0.053 ± 0.023; p < 0.001). In order to differentiate AD from non-AD patients, a decision tree was constructed. The diagnostic accuracy of the decision tree that contained Aβ1-42, Aβ1-40, P-tau181P, and the Aβ1-42/Aβ1-40 ratio was significantly better than the diagnostic accuracy (80% versus 74%) of the decision tree without Aβ1-40 and the Aβ1-42/Aβ1-40 ratio (p < 0.001). In conclusion, no difference in Aβ1-40 CSF levels was found between AD and non-AD patients, but adding CSF Aβ1-40 and the CSF Aβ1-42/Aβ1-40 ratio to a biomarker-based decision tree, might have an added value for discriminating AD from non-AD patients in case of intermediate CSF P-tau181P values.

Comparison of Two Analytical Platforms for the Clinical Qualification of Alzheimer's Disease Biomarkers in Pathologically- Confirmed Dementia

Combined analysis of the Alzheimers disease (AD) biomarkers amyloid-β(1-42) (Aβ(1-42)), total tau (T-tau), and hyperphosphorylated tau (P-tau(181P)) in cerebrospinal fluid (CSF) reduces the uncertainty associated with clinical dementia diagnosis. The present study evaluated the diagnostic accuracy of the CSF biomarker concentrations obtained with a multi-analyte Luminex assay (INNO-BIA AlzBio3) in comparison to single-analyte ELISA tests (INNOTEST). Data from 66 pathologically-confirmed dementia patients (51 AD and 15 non-AD) and 95 controls were included. Cut-off values were determined for each individual biomarker determined using both methods for different diagnostic challenges (dementia-controls; AD-controls; AD-non-AD). Comparing the diagnostic accuracy of individual cut-off values between INNO-BIA and INNOTEST, no relevant differences could be identified. Logistic regression was used in addition to identify the best combination of predictor variables (biomarkers). Discrimination of dementia patients from controls using Aβ(1-42) and T-tau yielded a diagnostic accuracy of 0.87 and 0.90 for INNO-BIA and INNOTEST, respectively. Discriminating AD patients from controls, the diagnostic accuracy was 0.90 and 0.93 for INNO-BIA and INNOTEST, respectively. Optimal discrimination of AD and non-AD patients was achieved by combining Aβ(1-42) and P-tau(181P) (diagnostic accuracy = 0.86). In conclusion, which AD biomarkers or combination thereof are most informative is dependent on the differential diagnosis, but the clinical value of these markers in each of the differential diagnoses is independent of the method by which concentrations are determined. Since the clinical value of the ELISA (INNOTEST) and Luminex (INNO-BIA) tests is comparable, further research to select the most suitable analytical platform for routine CSF biomarker measurements is needed.

Increased CSF α-synuclein levels in Alzheimer's disease: Correlation with tau levels

Given the difficult clinical differential diagnosis between Alzheimers disease (AD) and dementia with Lewy bodies (DLB), growing interest resulted in research on α‐synuclein as a potential cerebrospinal fluid biomarker (CSF) for synucleinopathies.