Elevated vasoactive intestinal peptide concentrations poorly predict VIPoma

VIPoma is a rare neuroendocrine tumor (NET) that is challenging to diagnose. While VIP concentrations are elevated in VIPoma, the optimal threshold for diagnostic purposes is not well defined. We aimed to study this in a single-institution population. We obtained results from vasoactive intestinal peptide (VIP) tests from 2011 to 2023 and reviewed the medical record of patients who had concentrations greater than our established assay-specific reference limit of 75 pg/mL. We compared plasma VIP concentrations between patient cohorts with and without VIPoma and determined the optimal threshold for VIP concentrations to predict a VIPoma in this population. Seventy-six patients met the selection criteria. Of these, nine cases of VIPoma were diagnosed. All patients had chronic diarrhea, and five patients had a previous diagnosis of a pancreatic neuroendocrine tumor (PNET). VIP concentrations drawn for acute/episodic diarrhea or flushing/diaphoresis did not lead to a diagnosis of a VIPoma. Mean VIP concentration was increased in patients with a VIPoma relative to those without, but the difference was not statistically significant (508 pg/mL vs 223 pg/mL, P = 0.31). Using the threshold of 75 pg/mL, the positive predictive value for a VIPoma was 12%. The optimal VIP threshold was 442 pg/mL (OR: 11.96, 95% CI: 2.00-79.69, P = 0.01), with statistically significant odds ratios starting at 200 pg/mL. Our findings suggest that elevated VIP concentrations are not predictive for a VIPoma and most patients with elevated VIP do not have a VIPoma. We recommend that VIP only be drawn in certain clinical scenarios to avoid unnecessary medical investigations.