Hi Amy! I have exactly the same chronic diseases that you have along with IBS. For me, coughing up blood is more a symptom of a Bronchiectasis exerbation. I experienced that this past December along with increased chest congestion . A two week course of Amoxicillin Clav 875 antibiotic cleared me right up. My understanding is that you need to treat this because while MAC is a slow growing disease that may not need to be treated if asymptomatic; Bronchiectasis is an incurable condition that can cause further damage to your lungs. Also, you will feel much better!! Hope this helps!
Dee