My husband Bruce's ID/Pulmonologist at Johns Hopkins in Bayview, Maryland (east of Baltimore) has requested multiple sputum cultures for different reasons. He does a monthly submission to our local Quest lab which involves two tests; one for non-MAC bacteria which takes about 2 weeks for results, and one for MAC which takes 6 weeks. He has also provided sputum for pseudomonas testing and for various fungi.
His doctor told him at the start of his MAC treatment in September 2021 that regular sputum cultures were part of the Hopkins' MAC protocol.
Earlier in the year Bruce's immunologist, also at Hopkins, added to the mix by having him submit sputum cultures and bloodwork through Quest for testing at a specialized lab in Utah.
All of the results to date have given the doctors, and us, a pretty good indication of whether the treatment is working or not. A lot of changes have been made along the way with substituting and adding antibiotics both to deal with negative side effects or new infection issues.
It seems from the discussions among this group that what we are experiencing - all of the cultures and testing - is pretty much the norm.
Perhaps your suggestion that smaller labs or additional costs are a factor. It seems curious especially since MAC, Pseudomonas, Bronchiectasis and other types of lung diseases and infections are becoming more prevalent.