Background: There is a need to use noninvasive markers in refining the management of ulcerative colitis to reduce the number of unnecessary colonoscopies, which facilitates the follow-up of activity and the response to treatment. Aim: Postulation of a sensitive, specific, simple and noninvasive score to monitor disease activity in ulcerative colitis. Methods: A case-control study was conducted: 168 patients with ulcerative colitis, 40 healthy individuals, and 60 patients for validation. Patients were divided into new diagnosis (n = 50), clinical remission (n = 60), and relapse (n = 58). The main outcome measures if the score correlates with clinical, endoscopic and histopathological characteristics and if it correlates with deep remission. Results: A scoring system was established composed of lactoferrin at a cutoff of 148.5 μg/mL, neutrophil lymphocyte ratio at a cutoff of 2.35, erythrocyte sedimentation rate at the first hour at a cutoff of 29.5 mm/h, C-reactive protein at a cutoff of 3.85 mg/L, mean platelet volume at a cutoff of 8.8 fL, fecal white blood cells at a cutoff of 9 cells/HPF, and fecal red blood cells at a cutoff of 6 cells/HPF. A score ≥5 can detect 94% of cases of UC as determined by the receiver operating characteristic curve with a sensitivity of 94% and a specificity 100%, AUC 0.92, SE 0.05, p = 0.001, 95% CI 0.82–1.1. In the validation group, it identified severely affected patients with a sensitivity of 95% and a specificity of 85.7%. Conclusions: This easily applied and reproducible noninvasive activity score showed high performance in predicting disease activity and deep remission in ulcerative colitis.