Effect of Patient-Specific Preanalytic Variables on CSF Aβ1-42 Concentrations Measured on an Automated Chemiluminescent Platform

Assessment of Preanalytical Cerebrospinal Fluid Handling and Storage Factors on Measurement of Aβ1-42, Aβ1-40, and pTau181 Using an Automated Chemiluminescent Platform

BACKGROUND

Standardizing cerebrospinal fluid (CSF) laboratory protocols will improve the reliability and availability of clinical biomarker testing required for prescription of novel Alzheimer disease (AD) therapies. This study evaluated several preanalytical handling and storage factors common to β-amyloid1-42 (Aβ1-42), β-amyloid1-40 (Aβ1-40), and phosphorylated tau (pTau181) concentrations including storage at different temperatures, extended cap contact, various mixing methods, and multiple freeze-thaw cycles.

METHODS

Aβ1-42, Aβ1-40, and pTau181 concentrations were measured using LUMIPULSE G1200 automated assays. Samples were collected in polypropylene tubes of various volumes. Sample cap-contact was evaluated by storing samples in upright and inverted positions at either 4°C for 1 week or -80°C for 1 month. To assess mixing methods, samples were freeze-thawed and mixed by inversion, vortex, horizontal roller, or unmixed prior to assay sampling. The impact of successive freeze-thaw cycles was assessed through freezing, thawing, and analyzing CSF samples.

RESULTS

Short-term storage at 4°C did not affect Aβ1-42, Aβ1-40, or pTau181 measurements in any tube type. Tube cap contact affected Aβ1-42 in 2.5 mL tubes and pTau181 levels in 10 mL tubes. No difference was observed between mixing methods. After 4 freeze-thaw cycles, Aβ1-42 significantly decreased but Aβ1-40 remained unchanged. Utilizing the Aβ1-42/Aβ1-40 ratio, Aβ1-42 values normalized, maintaining ratio values within ±5% of baseline measurements.

CONCLUSIONS

Storage of CSF at 4°C for 1 week or -80°C for 1 month did not significantly affect Aβ1-42, Aβ1-40, pTau181, or associated ratio measurements. Tube cap-contact impacted pTau181 and pTau181/Aβ1-42 values in larger tubes. Mixing methods are equivalent. The Aβ1-42/Aβ1-40 ratio compensates for freeze-thaw variability up to 4 cycles.

Cerebrospinal Fluid Biomarkers Predict Gait Outcomes in Idiopathic Normal Pressure Hydrocephalus

Background and Objectives

The assessment of biomarkers in selecting patients with idiopathic normal pressure hydrocephalus (iNPH) for shunt surgery has been limited to small cohort studies and those with limited follow-up. We assessed the potential for CSF biomarkers in predicting immediate response to CSF tap test (TT) and long-term response after shunt surgery.

Methods

CSF was obtained from patients with iNPH referred for CSF TT after baseline assessment of cognition and gait. CSF neurofilament light (NfL), β-amyloid 42 (Aβ_1–42), β-amyloid 40 (Aβ_1–40), total tau (tTau), and phosphorylated tau 181 (pTau181) and leucine-rich alpha-2-glycoprotein-1 (LRG1) were measured by ELISA. The ability of these measures to predict immediate improvement following CSF TT and long-term improvement following shunt surgery was compared by univariate and adjusted multivariate regression.

Results

Lower NfL, pTau181, tTau, and Aβ_1–40 were individually predictive of long-term improvement in gait outcomes after shunt surgery. A multivariate model of these biomarkers and MRI Evans index, adjusted for age, improved prediction (area under the receiver operating curve 0.76, 95% confidence interval 0.66–0.86). tTau, pTau181, and Aβ_1–40 levels were statistically different in those whose gait improved after CSF TT compared with those who did not. Using a multivariate model, combining these markers with Evans index and transependymal flow did not significantly improve prediction of an immediate response to CSF TT.

Discussion

A combination of CSF biomarkers can predict improvement following shunt surgery for iNPH. However, these measures only modestly discriminate responders from nonresponders following CSF TT. The findings further suggest that abnormal CSF biomarkers in nonresponders may represent comorbid neurodegenerative pathology or a predegenerative phase that presents with an iNPH phenotype.

Core Alzheimer's disease cerebrospinal fluid biomarker assays are not affected by aspiration or gravity drip extraction methods

BACKGROUND

CSF biomarkers are well-established for routine clinical use, yet a paucity of comparative assessment exists regarding CSF extraction methods during lumbar puncture. Here, we compare in detail biomarker profiles in CSF extracted using either gravity drip or aspiration.

METHODS

Biomarkers for β-amyloidopathy (Aβ1-42, Aβ1-40), tauopathy (total tau), or synapse pathology (BACE1, Neurogranin Trunc-p75, α-synuclein) were assessed between gravity or aspiration extraction methods in a sub-population of the Australian Imaging, Biomarkers and Lifestyle (AIBL) study (cognitively normal, N = 36; mild cognitive impairment, N = 8; Alzheimer's disease, N = 6).

RESULTS

High biomarker concordance between extraction methods was seen (concordance correlation > 0.85). Passing Bablock regression defined low beta coefficients indicating high scalability.

CONCLUSIONS

Levels of these commonly assessed CSF biomarkers are not influenced by extraction method. Results of this study should be incorporated into new consensus guidelines for CSF collection, storage, and analysis of biomarkers.