LAUSR

We read with interest the multiomic studies by Kong et al and Chen et al examining gut microbiome–metabolome interactions and potential diagnostic and classification biomarkers in colorectal cancer. 2 Largescale, multicentre, multisample, longitudinal studies are imperative to understand complex relationships between the metabolome and digestive diseases. Analysis of matched blood and stool can advance biomarker development and aid mechanistic exploration, providing samples are collected and stored appropriately. Buffered kits are commercially available for stable transfer of stool samples to storage. However, stabilisation of metabolites from blood requires freezing that may be confounded by transport and storage variables including time to whole blood centrifugation, time to freezing and freezing temperature. The gold standard of immediate sample separation and freezing 5 must be carefully balanced with pragmatic protocols, needed to facilitate standardised, costeffective collection by busy clinical research facilities across multiple recruiting sites. In preparation for the CDmetaRESPONSE precision medicine multicentre study (www.ibd-response.co.uk), we undertook this research to assess the impact of sample collection, shipping and storage on circulating metabolites. We collected whole blood in lithium heparin tubes from five nonfasting adult participants. Ten conditions were tested to model varying storage times of whole blood at 4°C from collection to central lab centrifugation, subsequent storage time of plasma at 4°C before freezing and the impact of long-­term­storage­at­−20°C­or­−80°C.­We­ performed metabolomics using both liquid chromatography–mass spectrometry (LCMS) and nuclear magnetic resonance Letter