Laboratory Test Overuse and Compliance With Minimum Retesting Intervals in a Portuguese Healthcare Network.

Background Laboratory test overuse is a well-recognized challenge in modern healthcare, contributing to unnecessary costs, inefficient resource utilization, and potential patient harm. Inappropriate repeat testing, particularly outside recommended minimum retesting intervals (MRIs), represents a measurable target and actionable strategy to improve laboratory demand management. This study evaluated MRI compliance across multiple clinical settings and quantified the potential impact of MRI-based hard-stop restrictions. Methodology A retrospective observational study was conducted at a regional healthcare network in Northeast Portugal, including three hospitals and 14 primary care centers. All laboratory requests for 77 biomarkers performed between January 2023 and December 2024 were analyzed. Repeat tests were classified as appropriate or inappropriate based on established MRI recommendations. Patterns were compared across primary care, hospital outpatient, and inpatient/emergency settings. Statistical comparisons were performed using chi-square and z-tests for proportions. Potential cost savings were estimated based on reagent costs. Results Among 3,012,396 tests, 21.4% were performed outside recommended MRI thresholds. Inappropriateness rates were significantly different across care settings (p < 0.001): 6.7% in primary care, 15.4% in hospital outpatient care, and 31.4% in hospital inpatient care. Overutilization was particularly pronounced for frequently requested biomarkers, as 10 of the 11 most frequently prescribed biomarkers showed overall inappropriateness rates ranging from 24.4% to 32.5%. The simulated implementation of MRI-based hard-stop rules was projected to reduce laboratory expenditure by 14.2% (€119,281.93 annually). Notably, 38.5% of the estimated savings were attributable to B-type natriuretic peptide alone. Conclusions Substantial non-compliance with MRI recommendations was identified across all levels of care, particularly in the hospital inpatient setting. These findings highlight the need for targeted laboratory demand management strategies, especially in high-intensity clinical environments. MRI-based interventions, including electronic decision-support tools such as hard-stop policies, may represent effective and sustainable approaches to improve test appropriateness, reduce healthcare costs, and minimize patient harm associated with unnecessary diagnostic cascades.