This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Inflammatory Bowel Disease, Subject name: Medicine
Best screening test for Crohn's disease is: 
Select and explain. 
A. A.S.C.A., B. P-ANCA, C. Fecal alpha 1 anti -trypsin, D. Fecal calprotectin
A: A.S.C.A.
Answer: A: A.S.C.A. 
Explanation: ASCA-positive (anti-saccharomyces cerevisae antibody) seen with 70% of CD and 15% of UC patients. p-ANCA positivity is found in about 60-70% of UC patients and 5-10% of CD patients Fecal calprotectin levels correlate well with histologic inflammation, predict relapses, and detect pouchitis