Diagnostic value of fasting plasma peptide concentrations in patients with chronic diarrhea

Abstract

To evaluate the utility of screening for multiple gastrointestinal peptides in the evaluation of patients with chronic diarrhea, we studied 193 patients referred for evaluation of chronic diarrhea and eight patients with known peptide-secreting tumors as a reference group. Fasting plasma samples were assayed for motilin, neurotensin, pancreatic polypeptide, somatostatin, substance P, vasoactive intestinal polypeptide, gastrin-releasing peptide, and calcitonin during a protocol evaluation for causes of chronic diarrhea. Although none of the referred patients were found to have tumors, abnormal levels of one or more peptides were found in 86 of 193 patients (45%). Abnormal plasma peptide levels were sometimes as high in these patients as in patients with known peptide-secreting tumors and would have led to mistaken diagnoses of tumors much more often than they would have led to correct diagnoses. The positive predictive value of elevation of any assayed peptide was < 2% at realistic prevalence rates for peptide-secreting tumors; the negative predictive value of a series of normal results was > 99%, but much of this was due to the rarity of these tumors. Patients with chronic diarrhea should not be screened routinely with a panel of plasma peptide assays in an effort to detect tumors; instead, peptide levels should be ordered selectively. Elevated fasting concentrations of the plasma peptides measured in this study are most likely epiphenomena due to diarrhea and should not be the sole basis for invasive diagnostic or surgical management of these patients.

Pathophysiology, Evaluation, and Management of Chronic Watery Diarrhea

“…However, due to the rarity of these tumors and low pretest probability, many positive results from these tests (especially borderline results) turn out to be false positives. 159 These tests should therefore almost never be considered early in the course of an evaluation.…”

Exposure to either gamma or a mixed neutron/gamma field irradiation modifies vasoactive intestinal peptide receptor characteristics in membranes isolated from pig jejunum

“…Th is n europeptide is often im plicated in certain gastrointestin al path ologies (K rejs 1987(K rejs , Koch et al 1991) and is considered as a diarrhetic agent. Furth erm ore elevated plasm a levels of V IP h ave been reported in cases of late radiation enteritis (Sch iller et al 1994).…”

Secretory diarrhea

“…An emp iri c tr ial of a b ile aci d-seq uesteri ng resin (eg, cholestyramine) may be more germane than direct measurement of bile acid absorption, which is often abnormal in patients with chronic diarrhea, because such measurements do not predict responsiveness to these agents [38,39]. Testing for secretagogue-induced diarrhea should be selective, based on findings of a tumor on CT scanning or presentation with a typical tumor syndrome because the pretest probability of tumor-associated diarrhea is very low [25]. Measurement of plasma peptide concentrations should be limited to those peptides with well-described tumor syndromes, gastrin, calcitonin, vasoactive intestinal polypeptide, and somatostatin.…”

“…Estimates of prevalence range from one per 1000 to one per 10,000 patients with chronic diarrhea. Thus, the chance of finding any of these tumors is very low in evaluation of a given patient [25].…”