Good question, as niether the medical community nor patients agree on what remission means. The CDAI is getting a lot of criticism and justly so, from docs.
Clinical trials like the LDN trial did use the CDAI, but it also used indicators like CRP, ESR (sed rate), and colonoscopy to check for mucosal healing. Right now there is some debate over whether mucosal healing (meaning a clean intestine, corroborated visually) should be one of the end goals of remission. Some doctors and patients use no symptoms as the definition for remission. Other docs, like Dr. Lutz, look at iron levels as yet another sign of remission - they tend to rise as Crohn's patients heal.
In my opinion, the definition of remission should mean a cessation of disease activity and include at a minimum: 1) no symptoms, 2) healthy HGB (hemoglobin, CRP, ESR and other lab markers, 3) a clean colonoscopy.
You can have no symptoms, like my daughter, but the disease is quietly festering, causing ulcers and strictures in the intestine, so that is not remission. You can also have healthy blood markers, but symptoms, so that is not remission. Similarly, if like outpatient, if you have a clean colonoscopy but you have symptoms, then that is not remission.