VIP Unit Converter
VIP Unit Converter
Convert vasoactive intestinal peptide between pg/mL, ng/L and pmol/L, with the fasting reference interval — and the two things that decide whether the result is worth anything: when the sample was taken and how fast it was frozen.
VIP converter
Mass ⇄ molarVIP 30 pg/mL, fasting, taken while the diarrhoea was active
The three units
pmol/L = pg/mL × 0.300589
derived from a molecular weight of 3,326.8 Da for the 28-residue mature peptide
- pg/mL = ng/L
- a picogram per millilitre and a nanogram per litre are the same concentration. North American reports print pg/mL; United Kingdom, Australasian and much of European practice prints pmol/L, and this is the conversion between the two
- × 0.300589
- the molar factor, from the mass of the mature 28-residue peptide, 3,326.8 daltons. The useful mental shortcut is that pmol/L is a little under a third of pg/mL, so dividing pg/mL by 3.3 gets close
- the cut-offs look different because the units are different
- Mayo’s <86 pg/mL and Canterbury Health Laboratories' <30 pmol/L fasting are 86 and about 100 pg/mL respectively. Some of the gap is method, but a reader comparing 86 with 30 without converting would conclude the two laboratories disagreed by a factor of three when they do not
- timing is part of the test
- VIP secretion by a VIPoma can be intermittent, so the specimen should be drawn while the diarrhoea is active and after a fast. A VIP taken during a quiescent phase can be normal in a patient who has a tumour
- handling is the other part
- VIP is a small peptide degraded by plasma proteases. Canterbury Health Laboratories requires the EDTA sample on ice, centrifuged at 4 °C, with the plasma frozen within an hour and no repeated freeze–thaw. Current instructions do not call for an aprotinin tube — that requirement belongs to the older radioimmunoassay protocols — but the cold chain is not optional
Worked example
VIP 30 pg/mL, fasting, taken while the diarrhoea was active
30 pg/mL = 30.0 ng/L — the same number in the other mass convention
30 × 0.300589 = 9.02 pmol/L, which is how a United Kingdom or Australasian laboratory would report it
Against the quoted interval, 0–86 pg/mL (0.00–25.85 pmol/L), 30 pg/mL is well inside it
Note what the conversion does to an apparent disagreement between laboratories. Canterbury Health Laboratories' cut-off of 30 pmol/L is about 100 pg/mL; Mayo's is 86 pg/mL, which is 25.85 pmol/L. Set 86 against 30 without converting and the two look threefold apart
Because the sample here was fasting and drawn during active diarrhoea, a normal result is informative — but Mayo states that the absence of an elevated VIP does not rule out malignancy, so it is not an exclusion
The diarrhoea a VIPoma causes, and how it differs
| Feature | VIPoma (secretory) | Osmotic or dietary diarrhoea |
|---|---|---|
| Volume | High — usually more than 700 mL per 24 hours, often several litres | Usually smaller |
| Effect of fasting | Persists; the secretion is driven by the hormone, not by what was eaten | Improves or stops |
| Stool osmotic gap | Low — the fluid is secreted, not drawn in by unabsorbed solute | High |
| Potassium | Hypokalaemia, often severe, from the potassium lost in the stool | Usually preserved |
| Acid–base and other | Metabolic acidosis from bicarbonate loss; achlorhydria; flushing; hypercalcaemia in some | Not typical |
| Plasma VIP | Raised, often several times the upper limit | Normal, or mildly raised for another reason |
Collection and handling, and what a mild elevation usually means
| Requirement or cause | Detail |
|---|---|
| Fasting | Canterbury Health Laboratories quotes its interval for a fasting adult |
| Timing | Draw while the diarrhoea is active — VIP release can be intermittent and a quiescent-phase sample may be normal |
| Tube | EDTA (lavender top). Current instructions at Mayo, Children’s Minnesota and CHL specify plain EDTA; an aprotinin tube is not required, though it was used with the older radioimmunoassays |
| Cold chain | On ice to the laboratory, centrifuged at 4 °C, plasma frozen within an hour, no repeat freeze–thaw |
| Mild elevation — bowel ischaemia | Recognised non-specific cause |
| Mild elevation — renal impairment | Reduced clearance of a small peptide |
| Mild elevation — congestive cardiac failure | Recognised non-specific cause |
| Assay sensitivity | Mayo notes its assay’s sensitivity may be lower than the previous radioimmunoassay, and that results cannot be read as absolute evidence for or against malignancy |
One syndrome, a narrow window, and a cold chain
Vasoactive intestinal peptide is a 28-residue neuropeptide that relaxes smooth muscle and drives intestinal secretion of water and electrolytes. It is measured for one practical reason: suspected VIPoma, a rare pancreatic neuroendocrine tumour that causes the WDHA syndrome of watery diarrhoea, hypokalaemia and achlorhydria. The diarrhoea that justifies the test has a particular character. It is high volume — usually more than 700 millilitres a day and often several litres — it is secretory rather than osmotic, so the stool osmotic gap is low, and crucially it persists while the patient is fasting, because the driver is circulating hormone rather than anything in the lumen. Alongside it sit hypokalaemia, often severe, and a metabolic acidosis from bicarbonate loss.
Two pre-analytical points decide whether the result means anything. The first is timing: secretion by a VIPoma can be intermittent, so the specimen should be drawn fasting and while the diarrhoea is active. A VIP taken during a quiescent phase can be entirely normal in a patient who has the tumour, and Mayo Clinic Laboratories states plainly that the absence of an elevated VIP does not rule out malignancy. The second is the cold chain. VIP is a small peptide and plasma proteases degrade it: Canterbury Health Laboratories requires the EDTA specimen on ice, centrifuged at 4 °C, with the plasma frozen within an hour and no repeated freeze–thaw cycles. An aprotinin-containing tube, often quoted for this analyte, is not called for by the current instructions at Mayo, Children’s Minnesota or Canterbury; that requirement belongs to the older extraction radioimmunoassays. Plain EDTA, kept cold and frozen quickly, is what the contemporary assays ask for.
Interpretation is asymmetric in the same way it is for glucagon on the sibling page. A VIPoma characteristically produces a VIP several times the upper limit of normal in a patient with the full syndrome. Mild elevations are common and largely non-specific: bowel ischaemia, renal impairment — VIP is a small peptide and renally cleared — and congestive cardiac failure all raise it. A VIP sitting just above the reference interval in someone without high-volume secretory diarrhoea is therefore weak evidence of anything, and the sensible next step is to look at the stool volume, the potassium and the response to fasting rather than to proceed straight to imaging.
The units repay a moment’s care because the two conventions in use differ by a factor of about three. Picograms per millilitre and nanograms per litre are the same number; picomoles per litre, which United Kingdom and Australasian laboratories report, is that number multiplied by 0.300589. Mayo’s cut-off of 86 pg/mL and Canterbury’s of 30 pmol/L are 25.85 pmol/L and roughly 100 pg/mL respectively — close to each other once converted, and apparently threefold apart if they are not.
Frequently asked questions
How do I convert VIP from pg/mL to pmol/L?
Multiply by 0.300589, from a molecular weight of 3,326.8 daltons for the 28-residue mature peptide. A VIP of 30 pg/mL is 9.02 pmol/L. Picograms per millilitre and nanograms per litre are the same number, and dividing pg/mL by about 3.3 is a serviceable mental approximation.
When should the VIP sample be taken?
Fasting, and while the diarrhoea is active. VIP release by a VIPoma can be intermittent, so a specimen drawn during a quiescent phase may be normal in a patient who has the tumour. Canterbury Health Laboratories quotes its fasting interval and recommends collection during a symptomatic episode.
Does a VIP sample need an aprotinin tube?
Not according to current instructions. Mayo Clinic Laboratories, Children’s Minnesota and Canterbury Health Laboratories all specify a plain EDTA tube; aprotinin belongs to the older radioimmunoassay protocols. What is required is the cold chain — on ice, centrifuged at 4 °C, plasma frozen within about an hour and not repeatedly thawed.
What VIP level suggests a VIPoma?
Not a mildly raised one. A VIPoma typically gives a value several times the upper limit — 86 pg/mL on the Mayo assay, about 100 pg/mL equivalent at Canterbury — in a patient with high-volume secretory diarrhoea and hypokalaemia. A stool volume below about 700 mL per 24 hours makes a VIPoma unlikely whatever the VIP shows.
What else raises VIP?
Bowel ischaemia, renal impairment and congestive cardiac failure are the recognised non-specific causes, which is why a marginal elevation without the clinical syndrome means little. Mayo also cautions that its assay’s sensitivity may be lower than the previous radioimmunoassay and that the result cannot be taken as absolute evidence for or against malignant disease.
Related calculators
References
- Mayo Clinic Laboratories. Test VIP: Vasoactive Intestinal Polypeptide, Plasma — reference value <86 pg/mL; EDTA plasma frozen immediately; VIPomas rarely associated with 24-hour stool volume <700 mL; absence of elevated VIP does not rule out malignancy. Accessed 2026.
- Canterbury Health Laboratories. Vasoactive Intestinal Peptide, Plasma — reference interval <30 pmol/L (adult fasting); EDTA on ice, centrifuge at 4 °C and freeze plasma within 1 hour; collect during a symptomatic episode. Accessed 2026.
- de Herder WW, Hofland J. Vasoactive intestinal peptide-secreting tumor (VIPoma). In: Feingold KR, et al., eds. Endotext. South Dartmouth, MA: MDText.com; updated 2023 — moderately elevated VIP in gastrointestinal ischaemia, renal insufficiency and congestive heart failure.
- Ghaferi AA, Chojnacki KA, Long WD, Cameron JL, Yeo CJ. Pancreatic VIPomas: subject review and one institutional experience. J Gastrointest Surg. 2008;12(2):382–393.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.