Micro- and nanoplastics as emerging clinical analytes: analytical validation, interpretive uncertainty, and laboratory actionability in human specimens.

Human exposure to micro- and nanoplastics (MNPs) is increasingly relevant to clinical toxicology, but the field is not yet ready for routine patient-level testing. This narrative review evaluates MNPs as emerging clinical analytes from the perspective of diagnostic laboratory medicine. The central question is how laboratories can measure, interpret and act on toxicological information in human specimens without overstating immature evidence. Current studies have reported MNP-related signals in blood, urine, placenta, breast milk, lung tissue, vascular plaques and other tissues, yet comparisons are constrained by inconsistent definitions, heterogeneous matrices, variable sample preparation, incomplete contamination control, method-dependent reporting units and limited outcome-linked data. Particle-based methods such as micro-Fourier-transform infrared and Raman spectroscopy preserve size and morphology information but have practical detection limits and throughput constraints. Mass-based approaches such as pyrolysis-gas chromatography/mass spectrometry quantify polymer mass but can lose particle-level information and may be vulnerable to matrix interferences. Clinical laboratories should therefore treat MNP measurement as a high-complexity analytical problem requiring matrix-matched validation, procedural and field blanks, uncertainty estimates, orthogonal confirmation for consequential claims, and conservative interpretive comments. At present, MNP testing is best suited to research biomonitoring, occupational and public-health surveillance, exposure-source investigations and translational cohorts linking particle measurements to validated effect biomarkers. The review proposes reporting tiers, readiness levels and a laboratory roadmap to convert uncertain exposure signals into reproducible, interpretable and clinically responsible toxicological information.