What does a result of occult blood 3+ mean. the sample was taken during an attack of diverticulitis?

It just means there was a small amount of blood found in the stool. That fact that it is "Occult" means that it would not be visible to the human eye. It should be reevaluated in the future with your doctors to ensure it has stopped after your diverticulitis heals.

It means you need to see a doctor for further evaluation. Usually diverticulitis does not cause a positive occult blood. It is a screening test for abnormalities throughout the digestive tract and needs further testing to determine the cause. See your PCP or a gastroenterologist.