Those are questions for your doctor, I think. Every practice has a different methodology. For example, my doc wants a minimum of 2, and preferably 3, samples collected over 48 hours, refrigerated and submitted at one time.

At my clinic, which is a larger network, suspect NTM slides are smear-checked in the central lab, then go to the State Dept of Health where it is cultured to rule out TB, even if the smear was negative. (I believe that is because our area is considered high risk for TB.) If the state lab detects TB, the results are reported to the clinic & they decide whether/how to treat.

If the culture shows NTM, our clinic protocol has it sent on to the lab at NJH for sensitivity & colony count. If I had to guess, I would say our protocol is because the chair of our ID department has a working relationship with NJH, and feels it is most accurate. My daughter's clinic is part of our largest metro hospital, and they do their own cultures in-house, with sensitivity testing, but no colony counts. They require 2 samples.

So, your doctor, or the lab they use, can answer the questions about their exact process.
Sue