From metrological comparability to clinical continuity: authorising laboratory result reporting when changing measurement procedures

OBJECTIVES: To develop and apply an operational framework integrating metrological, analytical, clinical and risk evidence to authorise an output-specific reporting rule after a change in measurement procedure. METHODS: Four measurement procedure changes were evaluated: alanine aminotransferase (ALT) procedures with and without pyridoxal-5'-phosphate activation; follicle-stimulating hormone (FSH) reagent replacement; routine vs. short-turnaround-time (STAT) parathyroid hormone (PTH) procedures; and tacrolimus procedure replacement with retention of the previous procedure for contingency use. The pathway integrated metrological comparability and compatibility, operational equivalence, controlled correction to a target reporting scale, independent clinical verification, uncertainty-aware classification, risk assessment and surveillance. RESULTS: The framework produced four qualitatively distinct outcomes: no cross-procedure continuity for ALT; direct continuity for raw FSH results; PTH continuity only through a corrected STAT result; and routine use of the new tacrolimus procedure, with the previous one restricted to contingency testing. FSH showed 100 % pair-level compatibility (95 % CI 91.2-100 %) and nominal percentage of clinically acceptable concordance (PCAC) of 96.6 % (82.2-99.9 %). PTH raw compatibility was assumption-sensitive at 90.0 % (76.3-97.2 %) vs. 87.5 % (73.2-95.8 %); the corrected output increased compatibility to 95.0 % (83.1-99.4 %), with nominal PCAC of 100 % (83.2-100 %). Tacrolimus met the mean-difference criterion but showed excess residual scatter, raw compatibility of 70.0 % (53.5-83.4 %) and nominal PCAC of 65.0 % (40.8-84.6 %); exploratory correction was not authorised. CONCLUSIONS: Changes in measurement procedure should culminate in an authorised reporting rule integrating metrological, analytical, clinical and risk evidence. Regression alone cannot establish continuity or interchangeability.