Overuse of laboratory testing in hospitalized patients is a common form of low-value care and may contribute to patient discomfort, unnecessary downstream testing, inefficient use of healthcare resources, and increased costs. Although diagnostic stewardship interventions have reduced unnecessary laboratory testing in several high-income settings, evidence from Latin America remains limited, particularly regarding implementation processes and sustainability.

OPTIMIZAR is a multicenter, effectiveness-implementation hybrid type 2 study evaluating a multicomponent diagnostic stewardship intervention in internal medicine wards and intensive care units across public and private tertiary hospitals in Argentina. The intervention targets laboratory ordering practices through workflow redesign, operational support, clinician education, and audit and feedback, with local leadership teams supporting implementation at each site.

Effectiveness will be evaluated using an interrupted time series design with aggregated unit-level data collected before and after implementation. The primary outcome is monthly laboratory testing intensity, measured as Argentine Standardized Biochemical Units per occupied bed-day. Secondary outcomes include in-hospital mortality and hospital length of stay. Implementation outcomes will be assessed descriptively using the Reach, Effectiveness, Adoption, Implementation, and Maintenance framework.

The overuse of diagnostic laboratory testing in hospitalized patients is a well-recognized source of low-value care. Unnecessary testing may contribute to patient discomfort, iatrogenic anemia, false-positive findings, diagnostic cascades, prolonged hospitalization, increased workload for clinical teams, and inefficient use of healthcare resources. Diagnostic stewardship strategies have been proposed to improve the appropriateness of test ordering while maintaining patient safety. However, most available evidence comes from high-income healthcare systems, and there is limited evidence regarding the effectiveness, implementation, and sustainability of these interventions in Latin American hospitals.

OPTIMIZAR is a multicenter, effectiveness-implementation hybrid type 2 study designed to evaluate both the effectiveness and implementation of a multicomponent diagnostic stewardship intervention. The study will be conducted in internal medicine wards and intensive care units across public and private tertiary hospitals in Argentina. The intervention is implemented at the hospital unit level and is integrated into routine clinical practice.

The intervention consists of a multifaceted diagnostic stewardship bundle targeting laboratory ordering practices. Its components include: workflow redesign to define clear responsibility for daily laboratory ordering; operational support strategies such as sample reutilization for add-on testing and remote electronic order modification; structured educational sessions focused on diagnostic stewardship principles, healthcare costs, and the clinical utility of commonly ordered laboratory tests; and audit and feedback with periodic review of laboratory ordering patterns and structured feedback to clinical teams. Each participating site will establish a local leadership team responsible for contextual adaptation, stakeholder engagement, and implementation support.

Effectiveness will be assessed using an interrupted time series design with aggregated unit-level data collected during a baseline usual-care period and after implementation. The primary outcome is monthly laboratory testing intensity, measured as Argentine Standardized Biochemical Units per occupied bed-day. This metric is based on the Argentine laboratory billing and weighting system, which assigns standardized biochemical units according to the technical complexity and resource utilization of each laboratory test. The outcome will be calculated monthly for each participating unit as the total number of standardized biochemical units divided by the total number of occupied bed-days.

Secondary effectiveness outcomes include monthly in-hospital mortality and hospital length of stay. These outcomes will be evaluated to assess whether reductions in laboratory testing are achieved without evidence of patient harm. Interrupted time series models will be used to estimate baseline trends, immediate changes after implementation, and post-intervention changes in trend.

Implementation outcomes will be assessed using the Reach, Effectiveness, Adoption, Implementation, and Maintenance framework. These indicators will include the extent to which participating units and clinicians are exposed to the intervention, adoption of intervention components, fidelity to the planned implementation strategy, barriers and facilitators to implementation, and maintenance of the intervention over time. This study aims to generate evidence on whether a locally adapted diagnostic stewardship strategy can safely reduce low-value laboratory testing and be implemented sustainably in Argentine hospital settings.

Inclusion Criteria:

• Adult patients (≥18 years) hospitalized in participating internal medicine wards or intensive care units during the study period.

Exclusion Criteria:

• None at the individual level. The intervention is implemented at the unit level and applies to all admitted adult patients during the study period.

Individual participant data will not be shared. The study uses aggregated, anonymized unit-level data extracted from institutional systems.