High Gastrin Level and Parathyroid Adenomia

Hi,  I was recently diagnosed with a parathyroid andenoma.   My most recent calcium test only came back as 10.2 which is only borderline but earlier ones were in the high  11's.  PTH is 80, Prolactin is 23.3 (borderline), vitamin D was (high).  My doctor also ordered a gastrin level which came back at 837.  I was immediately sent for an abdominal CT scan which showed no tumers.  I'm going to see my GI doctor this week and pursuing surgeon for parathyroid surgery.  GI doctor is concerned that I might have a neuro endoctrine tumor because I have a sister who had one in her mid-50's. I  am 47.  Can you treat such a tumor?  I have had stomach problems for the past 10 years and have  taken Nexium and Zantac. I went thru times where I didn't take them but in the past few months have been taking both.  I'm off both now and doctor is going to re-do the blood in a couple of weeks.  I'm a little upset that my GI doctor didn't take a gastrin level earlier.  As soon as my sister was diagnosed, I had an endoscopy and colonoscopy ( 3 years ago) that came back clean.  I was trying to be pro-active.  Also, has anyone anyone every heard of having such elevated gastrin levels due to high calcium level?   What else can raise gastrin levels?   I read something about stress?  I believe they have  ruled out MEN 1 .  Any feedback would be appreciated.  I'm really nervous.  Thanks in advance.