Selecting Human Cohorts for Causal Testing of Qualitative Fibrinogen States: A methodological framework and decision worksheet for an open protocol program

This methodological article complements the five-study open protocol program for investigating acquired qualitative fibrinogen states. It addresses how to select the first human cohort so that positive and negative findings can distinguish a proposed mechanism from competing explanations.

The framework prioritizes the disease–question pair rather than the diagnostic label alone. Different populations may be appropriate for molecular state identification, concentration-standardized transfer, necessity or sufficiency testing, generator mapping, and investigation of regeneration after trigger withdrawal.

The document provides noncompensable feasibility and analytical requirements, a twelve-domain cohort comparison worksheet, and a GO / MODIFY / NO-GO decision record. Selection criteria include prior molecular evidence, measurable upstream exposure, functional endpoints, serial sampling, concentration–quality separation, treatment and comorbidity management, and the interpretability of negative results.

Chronic kidney disease and type 2 diabetes illustrate opportunities for carbamylation-related generator studies and longitudinal glycation assessment. These examples are not presented as a validated disease ranking or as evidence of autonomous feedback. The article also addresses selection bias, overadjustment, assay preservation, biological replication, and the limits of interpreting longitudinal normalization as causal reversal.

This work reports no original participant data. The selection framework and decision tools are proposed, unvalidated methodological resources intended to support transparent planning before recruitment and experimental implementation. They do not replace study-specific protocols, ethics approval, or subsequent validation in representative populations.

Version 2 expands this methodological companion to the qualitative fibrinogen open protocol program by integrating disease selection with human cohort design. The revised title is Selecting and Designing Human Cohorts for Causal Testing of Qualitative Fibrinogen States.

The framework addresses two linked decisions: which disease–question pair offers an interpretable mechanistic test, and how participants should be selected, compared, followed, and analyzed. Chronic kidney disease and type 2 diabetes illustrate complementary opportunities for generator mapping and longitudinal investigation, without establishing a universal disease ranking.

Major additions include:

• Prespecified estimands distinguishing molecular group differences, exposure–state associations, concentration-standardized function, and within-person change.
• Comparator selection, matching, stratification, exposure-based enrichment, and two-phase sampling.
• Explicit consideration of overmatching, collider bias, regression to the mean, and informative loss to follow-up.
• Donor-level replication, nested technical measurements, illustrative pilot sizes, and confirmatory sample-size planning.
• Balanced analytical batches, blinded evaluation, specimen traceability, and independent validation.
• GO/MODIFY/NO-GO criteria separating technical failure, inconclusive evidence, and results that challenge a bounded biological hypothesis.

The document includes four tables and three operational appendices covering candidate comparison, progression decisions, and cohort-design specifications.

This contribution reports no original participant data. The selection worksheet and progression framework are proposed tools and have not been validated. Illustrative sample sizes are not substitutes for study-specific calculations. Observational associations and longitudinal changes are distinguished from the stronger attribution questions addressed by purified transfer, selective perturbation, rescue, and phenocopy experiments.