VIP Blood Test Explained: What It Measures and Why It's Ordered

Vasoactive intestinal peptide (VIP) is a 28-amino-acid signalling peptide found in enteric and central neurons and in several peripheral tissues. Because a small group of neuroendocrine tumours secrete it in excess, laboratories offer a quantitative VIP assay as part of the gut hormone work-up. This page summarises what the published literature says the analyte is, how it is measured, the clinical situations in which measurement has been described, and the methodological caveats that researchers have raised. This page is for educational purposes only and is not medical advice; consult a licensed physician about any laboratory result, symptom or treatment decision.

What the analyte is and where it comes from

VIP belongs to the secretin–glucagon peptide superfamily and signals through the VPAC1 and VPAC2 receptors. A 2022 review of VIP/VPAC axis expression in immune-mediated inflammatory disorders described the peptide and its receptors as widely distributed across immune and mucosal tissues, and mapped associated microRNA signatures (PMID 35955723). In the gastrointestinal tract VIP is released from enteric neurons rather than from a single endocrine gland, which is one reason circulating concentrations are low in most people and sensitive to sampling conditions.

A review of the biochemistry of neuroendocrine tumours placed VIP among the gut peptides that can be measured when a functional tumour syndrome is suspected, alongside markers such as chromogranin A and other regulatory peptides (PMID 17382264). That review framed peptide measurement as one component of a staged biochemical and imaging assessment rather than a stand-alone answer.

What the VIP blood test measures

The test quantifies immunoreactive VIP in a blood specimen, usually plasma collected into a chilled tube containing an anticoagulant and often a protease inhibitor, although some laboratories validate serum. Most routine methods are immunoassays — historically radioimmunoassay, more recently enzyme immunoassay and related platforms — which detect antibody-recognised fragments of the peptide rather than directly sequencing it. Because different antibodies recognise different epitopes, numerical results are method-specific.

The review of neuroendocrine tumour biochemistry emphasised that gut peptide assays require careful specimen handling and that results must be read against the issuing laboratory's own method and reference interval (PMID 17382264). This page does not reproduce reference intervals, because those belong to the reporting laboratory and to the clinician who requested the test.

Specimen type matters

VIP has also been measured outside blood. A study of salivary neuropeptides, stress and periodontitis quantified VIP and related neuropeptides in saliva rather than plasma (PMID 28914594). Concentrations measured in one biological fluid cannot be read across to another, and research assays used in such studies are not necessarily the same assays used by clinical laboratories.

Why clinicians request VIP measurement

The dominant indication described in the literature is suspected VIPoma. An overview of VIP-secreting tumours characterised VIPoma as a rare functional neuroendocrine tumour, most often pancreatic, associated with a secretory diarrhoea syndrome and electrolyte disturbance, and described biochemical confirmation together with imaging and histology as part of the diagnostic pathway (PMID 35582098). In that setting the assay is used to support or weaken a clinical hypothesis generated by symptoms, not to screen unselected populations.

A second described context is the broader neuroendocrine tumour panel. The biochemistry review set out how multiple peptide and amine markers are combined when a functional syndrome is suspected, with the choice of analytes driven by the clinical picture (PMID 17382264). Beyond oncology, VIP measurement appears chiefly in research protocols rather than routine care.

What studies report about high VIP values

The most directly relevant recent evidence concerns how well a raised result performs as a predictor. A 2026 study of elevated vasoactive intestinal peptide concentrations reported that raised VIP results predicted VIPoma poorly in the population examined, meaning that most elevated values arose in people who did not have a VIP-secreting tumour (PMID 41498509). Researchers framed this as a positive predictive value problem typical of rare-disease testing: when the condition is uncommon, even a reasonably specific assay generates many results that are not explained by the disease.

The VIPoma overview described the characteristic clinical syndrome — profuse watery diarrhoea with resulting electrolyte and acid–base disturbance — as the context in which a markedly raised concentration carries weight (PMID 35582098). Taken together with the predictive-value finding (PMID 41498509), the published picture is that a number in isolation is far less informative than the same number alongside a compatible clinical syndrome and imaging.

What studies report about VIP in non-tumour settings

Several research groups have measured circulating or tissue VIP in conditions unrelated to neuroendocrine tumours. These studies describe group-level differences and do not establish diagnostic tests.

• Thyroid autoimmunity. A 2020 study reported that the vasoactive intestinal peptide axis was dysfunctional in patients with Graves' disease, examining the peptide and its receptor system rather than using VIP as a diagnostic marker (PMID 32747757).
• Immune-mediated inflammatory disorders. The 2022 VIP/VPAC expression analysis described altered axis expression across several inflammatory conditions and the microRNA signatures associated with it (PMID 35955723).
• Migraine. A 2026 study measured plasma CGRP, VIP and PACAP concentrations in migraine patients before and after treatment with anti-CGRP receptor monoclonal antibodies (PMID 42307444).
• Paediatric research. A 2019 study compared serum substance P and vasoactive intestinal peptide concentrations in infants with acute intussusception (PMID 31006358).
• Oral and periodontal research. The salivary neuropeptide study examined VIP alongside stress measures in periodontitis (PMID 28914594).

None of these reports positioned VIP as a stand-alone clinical test for the condition studied; each measured the peptide as a research variable within a defined cohort (PMID 35955723, PMID 32747757).

Contexts in which VIP has been measured

Symptoms Associated with VIP-Secreting Tumours: What Studies Report

The VIPoma overview described the syndrome associated with pathological VIP hypersecretion as large-volume watery diarrhoea with consequent potassium loss and acid–base disturbance, and discussed the tumour's rarity, typical pancreatic origin and management considerations (PMID 35582098). The neuroendocrine biochemistry review similarly linked functional gut peptide syndromes to characteristic secretory presentations that prompt targeted hormone measurement (PMID 17382264). These are descriptions of a tumour syndrome in the published literature; they are not a checklist for self-assessment, and any symptom concern belongs with a clinician.

Assay and interpretation caveats researchers have raised

1. Rare-disease arithmetic

The 2026 predictive-value study reported that elevated concentrations performed poorly as a predictor of VIPoma, which researchers attributed to the low prevalence of the tumour relative to the frequency of raised results (PMID 41498509).

2. Method-to-method variation

Discordance between laboratory methods is a general analytical problem, not unique to VIP. A 2023 systematic review of between-assay consistency among laboratory testing methods for neurosyphilis documented how different platforms measuring the same clinical question can disagree (PMID 37438105). The same principle explains why a VIP result from one laboratory should not be compared numerically with a result from another.

3. Diagnostic accuracy is a property of a population, not a number

Biomarker evaluation literature illustrates this well: a 2023 analysis of diagnostic serum biomarkers associated with ankylosing spondylitis assessed candidate markers in terms of discriminative performance rather than presenting raw concentrations as diagnoses (PMID 36459277), and a meta-analysis of circulating microRNAs for osteosarcoma in Asian populations pooled sensitivity and specificity estimates across studies to describe how well the markers separated cases from controls (PMID 27106278).

4. Physiological and analytical context

Interpretation of any circulating analyte depends on the estimating framework used; researchers evaluating novel metabolites to improve glomerular filtration rate estimation reported that the choice of measured markers changed the resulting estimate (PMID 37037191). For peptide hormones, pre-analytical variables such as fasting state, specimen chilling, time to centrifugation and concurrent medication are standard considerations raised in the neuroendocrine biochemistry literature (PMID 17382264).

What the published literature does not settle

The verified literature summarised here does not define a universal cut-off, does not support VIP as a general screening test, and does not establish the peptide as a diagnostic marker for the non-tumour conditions in which it has been measured (PMID 41498509, PMID 35955723). It also does not address the use of VIP or VIP-related peptides as administered compounds; the studies cited here measured endogenous peptide concentrations.

Interpretation of an individual result — including whether a value is raised, what might explain it, and what, if anything, should follow — rests with the clinician who requested the test and who has access to the symptoms, medications, specimen details and laboratory method behind the number. Again: this page is educational only and is not medical advice.

References

• Biochemistry of neuroendocrine tumours (Best Practice & Research Clinical Endocrinology & Metabolism, 2007)
• Vasoactive intestinal peptide secreting tumour: An overview (World Journal of Gastrointestinal Oncology, 2022)
• Elevated vasoactive intestinal peptide concentrations poorly predict VIPoma (Endocrine-Related Cancer, 2026)
• VIP/VPAC Axis Expression in Immune-Mediated Inflammatory Disorders: Associated miRNA Signatures (International Journal of Molecular Sciences, 2022)
• Vasoactive intestinal peptide axis is dysfunctional in patients with Graves' disease (Scientific Reports, 2020)
• CGRP, VIP and PACAP plasmatic levels in migraine patients before and after anti-CGRP(R) monoclonal antibodies treatment (Cephalalgia, 2026)
• Serum substance P and vasoactive intestinal peptide levels in infants with acute intussusception (Journal of International Medical Research, 2019)
• Salivary neuropeptides, stress, and periodontitis (Journal of Periodontology, 2018)
• Evaluation of between-assay consistency among laboratory testing methods for neurosyphilis: a systematic review (Sexual Health, 2023)
• Diagnostic serum biomarkers associated with ankylosing spondylitis (Clinical and Experimental Medicine, 2023)
• Diagnostic value of circulating microRNAs for osteosarcoma in Asian populations: a meta-analysis (Clinical and Experimental Medicine, 2017)
• Novel Metabolites to Improve Glomerular Filtration Rate Estimation (Kidney & Blood Pressure Research, 2023)