One high vip blood test one normal. was told vip can fluctuate & retested when symptomatic. is this the only way they can officially diagnose vipoma?

VIPoma: Presumably you have the cardinal symptoms and signs: watery diarrhea and low K. Yes, plasma VIP should be measured during symptoms, and it should be high. If this is a VIPoma or other neuroendocrine tumor, then it becomes important to localize it. CT/MRI/somatostatin receptor imaging. Most important: go to a center that specializes in this. These are rare, and average doc doesn't see much.