increased gastrin level

My 14 yr old has had abdominal pain for  6 wks.  They scoped her and everything was fine.  We know she has some level of reflux she is on prilosec.  She is not a milk drinker so has been on tums 1000 for most of her life.  We stopped them about 8 wks ago.  Her gasrtin blood levels came back at 400.  they want to do a nuclear test.  I am wondering about a ct scan.  I actually think stomach pain may be stress but I feel her odds of having a rare tumor are remote. Any advice?