Circulating Microplastics in Routine Peripheral Blood: Bedside-Accessible Raman Screening in Myocardial Infarction and Controls

Circulating micro- and nanoplastics (MNPs) have been linked to ischaemic heart disease, but the clinical evidence rests on bulk, mass-based assays applied to predefined polymer panels in blood obtained during invasive coronary procedures. Whether the same phenomenon can be captured from a routine bedside venipuncture, and what quality control that requires, has not been established. We applied a digestion-filtration protocol coupled to untargeted single-particle confocal Raman microspectroscopy to pre-procedural peripheral venous blood (8.0–10.0 mL per venipuncture) from eight healthy controls and six patients with acute myocardial infarction (AMI). Particles were assigned against the Open Specy reference library at a Pearson correlation threshold of 0.80. After blank subtraction, nine particles were recovered from 147.0 mL of blood: polyethylene (n = 4), polystyrene (n = 3), ethylene–vinyl acetate (EVA, n = 1) and polyurethane (PU, n = 1). Microplastics were detected in four of six AMI patients (66.7%) and two of eight controls (25.0%) (OR 6.00, p = 0.277), with particle densities of 0.093 and 0.043 particles/mL (p = 0.152). Control prevalence closely matched the 31.8% reported for coronary sampling in the reference clinical series, indicating that peripheral blood is not an empty compartment for this measurement. Sub-threshold assignments were characterised point by point across all thirteen samples with complete spectral output: of 126 points returning a polymer below 0.80, 28 also returned a graphite reference, and on every one of those 28, the graphite match ranked higher than the polymer, without exception. We characterise this as carbonaceous procedural background, and it forms the empirical basis of the assignment threshold. No contrast reached significance with the subject as the unit of analysis, and no inference about causality or clinical risk can be drawn from a cohort of this size. The contribution of this work is methodological: it shows that circulating microplastics can be recovered and chemically identified from routine peripheral venous blood drawn before any intervention, that untargeted assignment returns polymers absent from the panels used by current clinical assays, and that single-particle spectroscopy permits blank attribution and background characterisation that mass-based methods cannot provide.