A vasoactive intestinal polypeptide blood test measures VIP levels to help diagnose rare neuroendocrine tumors. Learn who needs it and what the results mean.
A vasoactive intestinal polypeptide (VIP) blood test measures how much VIP hormone is circulating in your bloodstream. It is ordered mainly when a doctor suspects a VIPoma, a rare neuroendocrine tumor that causes the pancreas to overproduce this hormone and triggers severe, watery diarrhea. Results are reported in picograms per milliliter (pg/mL), and most labs flag fasting values above 75 pg/mL as elevated.
What Is Vasoactive Intestinal Polypeptide?
VIP is a 28-amino-acid hormone made by the pancreas, the nerves of the intestinal tract, and the central nervous system. Because of its small polypeptide structure, VIP is cleared from the blood quickly, which is one reason sample handling matters so much for this test.
VIP belongs to the same polypeptide group as secretin and glucagon, hormones that help regulate digestion and blood sugar. Along with pancreatic polypeptide, it is one of the gut hormones an endocrine lab can measure when a neuroendocrine tumor is suspected.
In healthy people, VIP relaxes smooth muscle, widens blood vessels, and signals the intestine to release water and electrolytes. That action supports normal digestion. When a tumor releases large amounts of VIP, the intestine secretes far more fluid than the colon can absorb, producing the hallmark symptoms of a VIPoma.
Why Doctors Order a VIP Blood Test
Most clinicians order this test only after more common causes of chronic diarrhea have been ruled out. Typical reasons include:
- Profuse, watery diarrhea lasting weeks or longer, often more than 1 liter per day
- Low potassium (hypokalemia), low stomach acid (achlorhydria), or metabolic acidosis
- Flushing, low blood pressure, or elevated calcium
- Monitoring a known pancreatic neuroendocrine tumor or checking response to treatment
A VIP blood test is usually part of a broader panel rather than a stand-alone test. Other polypeptide names in that panel include gastrin, glucagon, and somatostatin, and each one points to a different tumor type.
| Test | What it measures | Typical use |
|---|---|---|
| VIP | Vasoactive intestinal polypeptide | Suspected VIPoma; chronic secretory diarrhea |
| Pancreatic polypeptide | PP from pancreatic islet cells | Part of a pancreatic neuroendocrine panel |
| Gastrin | Gastrin from stomach G cells | Zollinger-Ellison syndrome |
| Chromogranin A | General neuroendocrine marker | Supporting marker for many neuroendocrine tumors |
How to Prepare for the Test
Preparation and handling matter more for VIP than for most routine blood draws, because the hormone breaks down fast outside the body. Ask your doctor for specific instructions, but the general steps are:
- Fast for 8 to 12 hours. Water is fine and encouraged.
- Tell your doctor about proton pump inhibitors, octreotide or other somatostatin analogs, laxatives, and any diarrhea medication. Some may need to be paused before the draw.
- Have the sample drawn at a lab that handles chilled, frozen plasma. VIP is destroyed by polypeptide hydrolysis, so blood is collected in a chilled EDTA tube, spun down cold, and frozen quickly.
- Avoid a long tourniquet time and vigorous hand pumping, since hemolysis can distort the result.
If the lab is not familiar with this test, call ahead. A sample left at room temperature for an hour can read falsely low.
What Your Results Mean
Reference ranges vary by lab and assay, so always compare your number to the range printed on your own report. Common cutoffs are:
- Normal: generally under 75 pg/mL, with some labs using under 30 or under 50 pg/mL
- Mildly elevated: 75 to 200 pg/mL
- Markedly elevated: above 200 pg/mL, and often above 500 pg/mL in confirmed VIPomas
A high VIP level alone is not a diagnosis. Mild elevations can come from kidney failure, liver disease, intestinal ischemia, a non-fasting sample, or even chronic constipation. A markedly high fasting value combined with classic symptoms is what pushes doctors toward a full VIPoma workup.
Several other polypeptide examples appear in the same evaluation, including gastrin and glucagon, but each has its own normal range and its own tumor association.
Next Steps If VIP Is Elevated
When a first result is high, the usual next step is a repeat fasting draw to confirm the finding. From there, doctors typically order imaging such as CT, MRI, endoscopic ultrasound, or a Ga-68 DOTATATE PET scan to look for a pancreatic or intestinal tumor.
Treatment depends on what is found. Surgery can cure a localized VIPoma. When surgery is not an option, somatostatin analogs like octreotide reduce hormone output and diarrhea, while IV fluids and potassium replace what the body loses.
Anyone with these symptoms should work with an endocrinologist or a neuroendocrine tumor specialist rather than trying to interpret a single lab value on their own.
Limitations and Safety Notes
The VIP blood test is a specialized tool, not a screening test. It should not be ordered for occasional bloating, irritable bowel symptoms, or general fatigue, because false positives can lead to unnecessary imaging and anxiety.
No lab result replaces a clinical evaluation. If you have persistent watery diarrhea, dehydration, or unexplained weight loss, talk to a healthcare professional promptly. Severe electrolyte loss can become dangerous within days, and electrolyte replacement is often the first priority.
Frequently Asked Questions
What is a normal vasoactive intestinal polypeptide level?
Most labs consider a fasting VIP level under 75 pg/mL normal, though some use a cutoff of 30 or 50 pg/mL. Values are reported in picograms per milliliter, and reference ranges vary by assay. Always compare your result to the range printed on your own lab report.
Do I need to fast for a VIP blood test?
Yes. Fasting for 8 to 12 hours is standard, and water is allowed. Some medications, including proton pump inhibitors and somatostatin analogs like octreotide, may need to be held beforehand, so confirm the plan with your doctor.
Can a VIP blood test diagnose a VIPoma by itself?
No. An elevated VIP level supports the diagnosis, but doctors usually confirm it with a repeat fasting test, imaging, and often a tissue biopsy. Symptoms such as profuse watery diarrhea, low potassium, and low stomach acid are part of the overall picture.
This page provides educational research information and does not replace medical advice, diagnosis, or treatment.