Blood and Other Tests 
• Diagnosis can be confirmed with specific hormonal assays measuring the levels of gastrin, glucagon, insulin, 
  VIP, somatostatin or other hormones .
• An elevated serum gastrin level (often 10 times normal) and an elevated stomach basal acid output for those 
  who have not had surgery should raise suspicions of the Zollinger-Ellison syndrome and its associated 
  gastrinoma.
• Measurement of plasma proinsulin may be helpful for diagnosing an insulinoma.
• Low serum potassium levels caused by secretory diarrhea may indicate a VIPoma. $ Elevated levels of serum 
  somatostatin and diabetes with severe malabsorption should suggest a somatostatin-producing tumor .

Imaging 
• Chest x-ray.
• Abdominal CT and MRI scans. 
• Ultrasonography. This may be performed with a probe on the skin (transcutaneous), within the lumen of the 
  stomach (endoscopic) or directly on the pancreas during surgery (intraoperative).
• Pancreatic arteriography can diagnose about 50 percent of cases, for some tumors—insulinoma, for example—
  are rich in blood vessels and have a tumor "blush." This method is rarely used since the advent of ultrasound 
  and CT.