This test is used to help detect tumours producing vasoactive intestinal polypeptide (VIP) in individuals with chronic diarrheal diseases.
VIP is a hormone produced by a number of body tissues and is found mainly in the digestive system, where it stimulates the secretion of water, electrolytes (sodium, etc.), and digestive hormones by the pancreas. Tumours that produce VIP (VIPoma or Verner-Morrison syndrome) are very rare, and 90 % of them are located in the pancreas. The presence of a VIPoma causes very watery diarrhea (over 700 millilitres a day), a low blood potassium level (hypokalemia), and the absence, or a very large drop in the level, of hydrochloric acid secretion in the stomach (achlorhydria). VIP testing is used to investigate chronic diarrhea when other possible causes have been eliminated (infectious or inflammatory diseases, lactose intolerance, use of medications, etc.), and particularly when very watery diarrhea is accompanied by hypokalemia and achlorhydria.