Background The optimal treatment of colorectal cancer is surgical resection and primary anastomosis. Anastomotic leak can affect up to 20% of patients and creates significant morbidity and mortality, a leak is based on clinical suspicion and subsequent radiology. Peritoneal biomarkers have shown diagnostic utility in other medical conditions and could be useful in providing earlier diagnosis. This pilot study was designed to assess the practical utility of peritoneal biomarkers after abdominal surgery utilising an automated immunoassay system in routine use for quantifying cytokines. Method Patients undergoing an anterior resection for a rectal cancer diagnosis were recruited. A peritoneal drain was placed in the proximity of the anastomosis during surgery, and peritoneal fluid was collected at day 1 and 2 post-operatively, and analysed using the Siemens IMMULITE platform for IL-1β, IL-6, IL-10, CXCL8, TNF-α and CRP. Results 42 patients were recruited. Anastomotic leak was detected in 4 patients and a further 5 patients had other intra-abdominal complications. The IMMULITE platform was able to provide robust and reliable results from the analysis of the peritoneal fluid. A metric based on the combination of peritoneal IL-6 and CRP levels was able to accurately diagnose three anastomotic leaks, whilst correctly classifying all negative control patients including those with other complications. Conclusion This pilot study has demonstrated that a simple immune signature in surgical drain fluid could accurately diagnose an anastomotic leak at 48 hours post-operatively using instrumentation that is already widely available in diagnostic laboratories.

EL, EJ and RM are employees of Siemens Healthineers. Neither the funders nor Siemens Healthineers had any impact on the study design, data collection, data analysis, decision to publish or preparation of this manuscript.

This research was supported by the European Regional Development Fund via the Welsh Government Accelerate programme, a Wellcome Trust Institutional Translational Partnership Award (ITPA), a Cancer Research Wales Access to Patient Samples for Translational Research Award (ASTRA), and the Wales Data Nation Accelerator (WDNA) scheme.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Recruitment of patients for this study was approved by the Wales Cancer Biobank under reference no. 18/016 and conducted according to the principles expressed in the Declaration of Helsinki. The Wales Cancer Biobank is licensed by the Human Tissue Authority under the UK Human Tissue Act (2004) to store human tissue for research (licence no. 12107) and is approved as a Research Tissue Bank by Wales Research Ethics Committee (REC) 3.

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable.

Yes

All data produced in the present study are available upon reasonable request to the authors.