Introduction:Computed tomography (CT) with intravenous (IV) contrast is the method of choice for diagnosing and selecting treatments for surgical pathologies in patients visiting the emergency room (ER) for acute, nontraumatic abdominal pain.However, there are risks, high costs, and delays in medical attention associated with this modality.Studies have suggested performance of CT without venous contrast for diagnosing appendicitis.Nevertheless, no methodologically rigorous studies have evaluated CT without IV contrast performance when used as the main diagnostic tool for patients with acute abdominal pain.Objective: This study aims to evaluate the diagnostic performance of noncontrast abdominal CT and compare it with a reference standard (surgery/pathology or clinical follow-up) to detect surgical diseases in patients with acute abdominal pain.Design: This is a cross-sectional, diagnostic test study.Place: Hospital Universitario San Vicente Foundation (Medellín, Colombia).Materials and methods: This is a cross-sectional convenience sample diagnostic test study of consecutively selected patients who underwent noncontrast CT of the abdomen.All patients were those who presented to the ER with abdominal complaints.All patients who consented underwent a noncontrast and IV contrast CT scans.Two radiologists with different levels of expertise independently evaluated the noncontrast tomography images to specify the diagnostic findings.Final diagnoses were collected independently from the patients' clinical histories.Patients who did not undergo surgery, their clinical histories were reviewed during hospitalization.Those who were not hospitalized had their clinical course obtained by telephone 2 weeks after being discharged.Results: Of the 157 included patients, 19.1% underwent surgery because of an acute pathology.For noncontrast abdominal contrast tomography, values of 93.3% sensitivity (95% CI 82.7-100), 96.8% specificity (95% CI 93.4-100), 87.5% PPV (95% CI 74.4-100), 98.4% NPV (95% CI 95.8-100), 29.6 LR+ (95% CI 11.24-78.1),0.07 LR-(95% CI 0.02-0.26),and 97.4% diagnostic accuracy were obtained.The interobserver concordance had a kappa value of 0.88.Conclusion: Noncontrast abdominal CT performs well in differentiating medical vs surgical diseases in patients with acute abdominal pain.