Discriminating capacity of indole markers in the diagnosis of carcinoid tumors

Background: We evaluated the discriminating capacity of the indole markers urinary 5-hydroxyindoleacetic acid (5-HIAA), urinary serotonin, and platele t serotonin in the diagnosis of carcinoid tumors. Methods: Indole markers were measured in 688 patients with suspect-ed carci noid disease. The initial values of indole markers from patients in whom. a carcinoid tumor was confirmed during follow-up (n = 98) were used for ROC analysis. Two groups served as reference populations. The first consisted o f 45 healthy individuals ("healthy controls"). The second was a random samp le of 40 patients, drawn from the 590 (688 minus 98) patients with carcinoi d-like symptoms but without a carcinoid tumor ("clinically suspected patien ts"). Results: ROC curve analysis showed platelet-serotonin to have the highest d iscriminating capacity, especially in foregut carcinoids. Cutoff values for platelet serotonin obtained from ROC analysis. with healthy controls as re ference group (5.4 nmol/10(9) platelets) gave a sensitivity of 74%, specifi city of 91%, positive predictive value of 63%, and negative predictive valu e of 95% when applied to the initial 688 patients. Using the cutoff value w ith the clinically suspected patients as the reference group (9.3 nmol/10(9 ) platelets) gave a sensitivity of 63%, specificity of 99%, positive predic tive value of 89%, and negative predictive value of 93%. Indole markers wer e increased in 169 (25%) of 688 patients. In 76 (45%) of these 169 patients , a carcinoid tumor was present. Slight increases of markers were associate d with non-carcinoid neuroendocrine tumors, non-neuroendocrine tumors, and disturbed bowel motility. Conclusions: ROC curve analysis shows that platelet serotonin is the most d iscriminating indole marker for the diagnosis of carcinoid tumors. Platelet serotonin especially improves the diagnosis of carcinoids producing small amounts of serotonin. (C) 2000 American Association for Clinical Chemistry.