Designing a Prospective Human Study of Qualitative Fibrinogen Phenotypes: A proposed protocol framework integrating longitudinal sampling and ex vivo mechanistic studies

This methodological article proposes a framework for developing a prospective observational study of qualitative fibrinogen phenotypes, integrating longitudinal blood sampling with nested ex vivo mechanistic experiments. The intended main-study comparison concerns baseline clot half-lysis time in clinically defined persistent and reference groups, using purified fibrinogen at a standardized final concentration. An acute comparator is optional and requires a disease-specific justification. The framework separates an initial analytical and operational feasibility phase from a subsequently specified confirmatory study. The article addresses eligibility independent of laboratory results, recruitment, visit scheduling, specimen traceability, preparation quality, blinded assessment, and control of copurified components. It distinguishes invalid lysis curves from valid curves without an observed half-lysis time and explains why their indiscriminate exclusion can bias the primary comparison. Statistical planning separates participants from technical replicates, conditional from marginal group contrasts, baseline assay loss from longitudinal attrition, and exploratory analyses from confirmation. Illustrative sample-size calculations are presented with explicit assumptions and are not proposed as final recruitment targets. Nested laboratory modules include transfer to a defined recipient, orthogonal purification, depletion–reconstitution, and exposure of a common fibrinogen substrate to plasma. Activity-based budgeting and dependency-based scheduling connect these experiments to material requirements and operational capacity. Four tables summarize the protocol architecture, visit schedule, laboratory controls, and readiness gates. Two appendices provide records for protocol specification and submission readiness. Participant protection, consent, sample use, data governance, and the Brazilian ethics framework are also discussed. No participants have been recruited, no original results are reported, and no study approval is claimed. The disease population, institutions, laboratory procedures, collection volumes, financing, and final statistical plan must be specified before this framework becomes an executable protocol.