| 1 | Define the biological question before sourcing | Amyloid pathology: CSF amyloid-beta 42/40 ratio, CSF amyloid-beta 42, amyloid positron emission tomography, or validated plasma amyloid measures. | Record disease stage, cognitive status, medication exposure, fasting status where applicable, collection time, and the interval between collection and processing. | Confirm that the assay measures the intended pathology and is supported by analytical sensitivity, precision, linearity, interference, and matrix-comparison studies. | Amyloid biomarkers help identify Alzheimer-type amyloid pathology and support biologically defined research cohorts, but results should be interpreted with clinical and cognitive information. | Write inclusion criteria around the intended use: discovery, diagnostic support, prognosis, treatment response, or enrollment enrichment. Do not combine specimens collected for different purposes without harmonization. |
| 2 | Prioritize pre-analytical traceability | CSF, plasma, serum, and brain tissue with complete chain-of-custody documentation. | Capture tube type, collection method, processing delay, centrifugation conditions, aliquot volume, freeze-thaw count, storage temperature, and shipment conditions. CSF should be handled using low-binding collection materials when required by the validated protocol. | Require a documented standard operating procedure and acceptance limits for hemolysis, lipemia, sample volume, temperature excursions, and missing metadata. | Pre-analytical variation can materially affect low-abundance plasma biomarkers and can create apparent differences between countries or collection centers. | Use a common sample manifest and barcode-based tracking system. Require each collection site to submit representative process records and temperature-monitoring evidence before study activation. |
| 3 | Match the specimen to the biomarker’s biological concentration | Phosphorylated tau: CSF p-tau181 or p-tau217; plasma p-tau181, p-tau217, or p-tau231.
Neurodegeneration: CSF or plasma neurofilament light chain and total tau. | Plasma assays require strict control of hemolysis, platelet contamination, anticoagulant choice, and dilution effects because target concentrations may be low. | Evaluate limit of detection, limit of quantification, between-run precision, dilutional linearity, recovery, lot-to-lot consistency, and agreement with an orthogonal reference method or clinical comparator. | P-tau is associated with Alzheimer-type tau pathology, while neurofilament light chain is a broader marker of neuronal injury and is not specific to Alzheimer disease. | Use CSF when direct central nervous system measurement is essential; use plasma for scalable screening and longitudinal monitoring only after confirming assay performance in the intended population. |
| 4 | Require orthogonal and clinical validation | Pair fluid biomarkers with an independent comparator such as amyloid or tau imaging, cerebrospinal fluid reference measures, neuropathology when available, or longitudinal clinical assessment. | Use samples collected near the comparator assessment and document the time interval between biomarker collection, imaging, diagnosis, and cognitive testing. | Assess sensitivity, specificity, area under the receiver operating characteristic curve, calibration, reproducibility, and performance across disease stages and relevant subgroups. | Clinical validity is stronger when a biomarker consistently reflects a defined pathology or predicts a clinically meaningful outcome rather than merely separating small case-control groups. | Request validation datasets containing cognitively unimpaired individuals, mild cognitive impairment, Alzheimer disease dementia, non-Alzheimer neurodegenerative diseases, and age-matched controls. |
| 5 | Control population and geographic confounding | All major biomarker classes, including amyloid, p-tau, neurofilament light chain, and inflammatory markers. | Record age, sex, education, ancestry or genetic background where ethically permitted, kidney function, body mass index, vascular disease, diabetes, and current medications. | Test for site effects, batch effects, population-specific reference intervals, and covariate interactions. Predefine adjustment methods and avoid post hoc subgroup selection. | Plasma concentrations can be influenced by renal function, age, comorbidities, and assay platform. A threshold derived in one population may not transfer directly to another. | Build a geographically diverse cohort with harmonized clinical definitions. Include enough participants per region to evaluate transportability rather than treating location as an unexamined nuisance variable. |
| 6 | Use reference materials and proficiency testing | Quantitative assays for CSF or plasma amyloid-beta, p-tau, total tau, and neurofilament light chain. | Include blinded quality-control samples, duplicate specimens, pooled matrix controls, and repeat measurements across runs and sites. | Prefer methods linked to internationally recognized reference procedures or certified reference materials where available. Monitor coefficient of variation, drift, missingness, and inter-laboratory agreement. | Standardization improves comparability across studies and reduces the risk that an apparent biological signal is caused by analytical calibration differences. | Distribute a common quality-control panel to participating laboratories, establish predefined rejection rules, and conduct periodic blinded proficiency assessments throughout the project. |
| 7 | Assess regulatory, ethical, and operational feasibility | Human biospecimens and linked clinical data intended for discovery, validation, or clinical development. | Confirm informed consent scope, de-identification, permitted future use, export or transfer restrictions, biosafety procedures, storage duration, and data-quality completeness. | Document assay version, reagent or calibration changes, laboratory accreditation status, analytical validation reports, and procedures for handling amended protocols. | A biomarker is more clinically useful when it can be measured consistently, transferred legally, reproduced across laboratories, and integrated into a realistic care or trial workflow. | Complete country-specific ethics and material-transfer review early. Select sites based on documented sample quality, validated processes, clinical follow-up, and sustainable cold-chain capability rather than sample volume alone. |