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Background and Aims: Reliable noninvasive biomarkers are an unmet clinical need for the diagnosis of NASH. This study investigates the diagnostic accuracy of the circulating triggering receptor expressed on myeloid cells 2 (plasma TREM2) as a biomarker for NASH in patients with NAFLD and elevated liver stiffness. Approach and Results: We collected cross‐sectional, clinical data including liver biopsies from a derivation (n = 48) and a validation cohort (n = 170) of patients with elevated liver stiffness measurement (LSM ≥ 8.0 kPa). Patients with NAFLD activity scores (NAS) ≥4 were defined as having NASH. Plasma TREM2 levels were significantly elevated in patients with NASH of the derivation cohort, with an area under the receiver operating characteristics curve (AUROC) of 0.92 (95% confidence interval [CI], 0.84–0.99). In the validation cohort, plasma TREM2 level increased approximately two‐fold in patients with NASH, and a strong diagnostic accuracy was confirmed (AUROC, 0.83; 95% CI, 0.77–0.89; p < 0.0001). Plasma TREM2 levels were associated with the individual histologic features of NAS: steatosis, lobular inflammation, and ballooning (p < 0.0001), but only weakly with fibrosis stages. Dual cutoffs for rule‐in and rule‐out were explored: a plasma TREM2 level of ≤38 ng/ml was found to be an optimal NASH rule‐out cutoff (sensitivity 90%; specificity 52%), whereas a plasma TREM2 level of ≥65 ng/ml was an optimal NASH rule‐in cutoff (specificity 89%; sensitivity 54%). Conclusions: Plasma TREM2 is a plausible individual biomarker that can rule‐in or rule‐out the presence of NASH with high accuracy and thus has the potential to reduce the need for liver biopsies and to identify patients who are eligible for clinical trials in NASH.

Introduction:The chemical composition of feces plays an important role in human metabolism. Metabolomics and lipidomics are valuable tools for screening the metabolite composition in feces. Here we set out to describe fecal metabolite composition in healthy participants in frozen stools.Methods: Frozen stool samples were collected from 10 healthy volunteers and cryogenically drilled in four areas along the specimen. Polar metabolites were analyzed using derivatization followed by two-dimensional gas chromatography and time of flight mass spectrometry. Lipids were detected using ultra highperformance liquid chromatography coupled with quadruple time-of-flight mass spectrometry. The technical variation threshold was set to 30% in pooled quality control samples and metabolite variation was then assessed in four areas per specimen. A data-generated network using metabolites found in all areas was computed for healthy participants.Results: 2326 metabolic features were detected. Out of a total of 298 metabolites that were annotated we report here 185 that showed a technical variation of x< 30%. These metabolites included amino acids, fatty acid derivatives, carboxylic acids and phenolic compounds. Lipids predominantly belonged to the groups of diacylglycerols, triacylglycerols and ceramides. Metabolites varied between sampling areas (14%-80%). A network using metabolites present in all areas showed two main clusters, DAG lipids and phenyllactic acid. Conclusions:In feces from healthy participants, the main groups detected were phenolic compounds, ceramides, diacylglycerols and triacylglycerols. Metabolite levels differed considerably depending on the sampling area.