You may be worrying about
it a bit more than needed, but you certainly have good & valid questions which they should be able to answer to your satisfaction. Maybe she was just running the possibilities thru her head and MCTD was one of the things she was considering. Either way, your being perfectly reasonable in wanting to know more!
Sometimes we have to ask the questions because otherwise they assume we are one of the patients who don't read the labs, or don't want to know that level of detail. Once you have an established relationship with the Dr, they get to understand how involved a patient you are, and generally act accordingly.
I've been around Lupus & ANA results a long time, and that is a most unusual way they chose to report it. Generally they'd just say positive 1:40, and leave it at that. It's implied/understood that it's negative at the tire above the one they put on the lab result. Makes me wonder, are you in the US? Sometimes other countries do it differently.
Lynnwood, Lupus & Sjogren's Moderator, Dx: 2000DIAGNOSING LUPUS & HW's LUPUS 101
"Life is far too important to be taken seriously." - Oscar Wilde