Preoperative Laboratory, Imaging, and Risk Assessment Before Elective Colorectal Cancer Resection: What the Clinician Must Remember

Colorectal cancer (CRC) remains one of the most frequently diagnosed malignancies worldwide and a leading indication for major abdominal surgery, with a rising incidence among younger adults. Because CRC resection is a physiologically demanding procedure performed in a frequently comorbid, often anemic and malnourished population, the preoperative period represents a decisive window in which laboratory and diagnostic testing shapes staging, risk stratification, and optimization. This narrative review is deliberately confined to the preoperative window—from histological diagnosis to the day of elective, curative-intent colon or rectal resection—and synthesizes evidence retrieved from PubMed/MEDLINE, Scopus, and ScienceDirect together with current society guidelines. It is organized around four themes: (i) the core laboratory workup, including the complete blood count and preoperative anemia, iron studies, metabolic and hepatic panels, coagulation testing, and carcinoembryonic antigen (CEA); (ii) the diagnostic and staging workup, encompassing complete colonic evaluation, contrast-enhanced computed tomography, pelvic magnetic resonance imaging for rectal cancer, and the selective role of positron emission tomography; (iii) risk stratification and preoperative optimization, spanning patient blood management, nutritional assessment and albumin, computed-tomography-defined low skeletal muscle mass, frailty, functional capacity, prehabilitation, and glycemic control; and (iv) molecular characterization, distinguishing mismatch-repair/microsatellite-instability (MMR/MSI) testing—an established, widely recommended component of CRC evaluation—from genuinely emerging biomarkers such as circulating tumor DNA (ctDNA) and systemic inflammatory and prognostic nutritional indices. Differences between colon and rectal cancer, elective and emergency presentation, and upfront versus post-neoadjuvant surgery are signposted throughout. We further integrate these elements within contemporary guideline and Enhanced Recovery After Surgery (ERAS) frameworks, including the 2025 ERAS Society recommendations for elective colorectal surgery, and distill them into a practical, evidence-based preoperative checklist specifying thresholds, timing, interventions, and strength of supporting evidence. We emphasize that the prognostic power of postoperative ctDNA does not yet translate into ctDNA-guided treatment decisions outside clinical trials. The central message is that preoperative testing in CRC should be purposeful and stage- and risk-adapted rather than reflexive: each investigation should refine staging, modify perioperative management, or enable measurable optimization. Each risk domain is paired with the intervention it should trigger, the criteria identifying candidates for extended thromboprophylaxis are specified, and the systemic inflammatory indices are framed as a trigger for optimization rather than as prognostic commentary.