ANNALS EXPRESS: Serum and plasma 5-HIAA as an alternative to 24-hour urine 5-HIAA measurement.

Abstract

BackgroundNeuroendocrine tumours (NETs) are slow growing tumours known to secrete a variety of vasoactive peptides which give rise to symptoms of the carcinoid syndrome. The diagnosis and monitoring of patients with NETs is undertaken in many centres using 24h urinary measurement of 5-hydroxyindoleacetic acid (5-HIAA). However, 5-HIAA can also be quantified in plasma and serum.MethodsWe measured 5-HIAA concentration in 134 paired EDTA plasma and urine samples from 108 patients with known NETs and 26 healthy volunteers. We also compared 5-HIAA concentrations in paired serum and plasma samples (n=63), then analysed paired urine and serum samples (n=97). Furthermore, we examined the impact of renal impairment on serum 5-HIAA by analysing 5-HIAA in patients without NETs in different stages of chronic kidney disease, as indicated by the estimated glomerular filtration rate (eGFR).ResultsPlasma and urine 5-HIAA had very similar diagnostic sensitivities and specificities, with areas under the curve (AUC) on ROC analysis of 0.917 and 0.920 respectively. Serum and plasma 5-HIAA values showed good correlation but serum results demonstrated a positive bias, indicating the necessity for different serum and plasma reference intervals. There was an inverse correlation between eGFR and serum 5-HIAA concentration, with 5-HIAA increasing once the eGFR falls below 60 mL/min/1.73m(2).ConclusionThe measurement of both serum and plasma 5-HIAA can be used for the diagnosis and monitoring of patients with NETs. Provided renal function is taken into consideration, either of these tests should be incorporated into standard practice as an alternative assay to urinary 5-HIAA.