A single fasting plasma 5-HIAA value correlates with 24-hour urinary 5-HIAA values and other biomarkers in midgut neuroendocrine tumors (NETs).

OBJECTIVES 5-Hydroxyindoleacetic acid (5-HIAA) is used for the evaluation of neuroendocrine tumors (NETs) but currently requires a 24-hour urine collection. METHODS We developed a gas chromatography mass spectroscopy-based plasma 5-HIAA assay. We compared 24-hour urine 5-HIAA values against plasma 5-HIAA values in 115 mixed-variety patients with NETs and in a subset of 72 patients with only small bowel NETs. We also compared the information gained from urinary and plasma 5-HIAA values with other biomarkers of midgut NET activity to determine the plasma assay's clinical implications. RESULTS In a group of 115 patients with all types of NETS, in a subset of patients with midgut NET and in a subgroup of midgut NETS with liver metastasis, the correlation between the urine and fasting plasma 5-HIAA values were statistically significant (P ≤ 0.0001). Comparison of the proportion of normal or abnormal urinary and plasma 5-HIAA values to the proportion of chromogranin, serotonin, neurokinin, or pancreastatin values that were in the normal or abnormal range yielded essentially identical information. CONCLUSIONS Plasma fasting 5-HIAA values are proportional to urinary 5-HIAA values and yielded identical clinical correlation with other biomarkers.