DIAGNOSTIC-VALUE OF FASTING PLASMA PEPTIDE CONCENTRATIONS IN PATIENTSWITH CHRONIC DIARRHEA

To evaluate the utility of screening for multiple gastrointestinal pep tides in the evaluation of patients with chronic diarrhea, we studied 193 patients referred for evaluation of chronic diarrhea and eight pat ients with known peptide-secreting tumors as a reference group. Eastin g plasma samples were assayed for motilin, neurotensin, pancreatic pol ypeptide, somatostatin, substance P, vasoactive intestinal polypeptide , gastrin-releasing peptide, and calcitonin during a protocol evaluati on for causes of chronic diarrhea. Although none of the referred patie nts were found to have tumors, abnormal levels of one or more peptides were found in 86 of 193 patients (45%). Abnormal plasma peptide level s were sometimes as high in these patients as in patients with known p eptide-secreting tumors and would have led to mistaken diagnoses of tu mors much more often than they would have led to correct diagnoses. Th e positive predictive value of elevation of any assayed peptide was <2 % at realistic prevalence rates for peptide-secreting tumors; the nega tive 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 pepti de assays in an effort to detect tumors; instead, peptide levels shoul d be ordered selectively. Elevated fasting concentrations of the plasm a peptides measured in this study are most likely epiphenomena due to diarrhea and should not be the sole basis for invasive diagnostic or s urgical management of these patients.