Analytical and preanalytical validation of a new mass spectrometric serum 5-hydroxyindoleacetic acid assay as neuroendocrine tumor Marker

Background: Serum 5-hydroxyindoleacetic acid (5-HIAA) could replace the determination of 24-h urinary 5-HIAA for diagnosis and follow-up of neuroendocrine tumors (NETs). We developed and validated a straightforward liquid chromatography tandem mass spectrometry (LC-MS/MS) assay for serum 5-HIAA. Methods: We used serum samples from healthy volunteers (n = 136) and patients suspected or followed for NET (n = 129). Samples were spiked with 5-HIAA-D-2, extracted and quantified by LC-MS/MS. We studied the effects of sample storage, sample device, a meal and diurnal variation on serum 5-HIAA. Furthermore, we established a reference range for serum 5-HIAA and compared our assay with a urinary 5-HIAA HPLC assay and a commercial plasma chromogranin A (CgA) immunoassay. Results: Our LC-MS/MS assay is sensitive (LOQ 5 nmol/L), has a wide assay range (5-10,000 nmol/L) and short analysis time (7 mm). 5-HIAA in serum is stable for several days in various temperatures and during five freeze-thaw cycles. We found no diurnal variation (p >= 0.20) and a meal had no effect on serum 5-HIAA (p = 0.89). We suggest an upper reference limit of 123 nmol/L for serum 5-HIAA. The area under curve (AUC) in receiver operator characteristics (ROC) analysis was 0.83 for urinary 5-HIAA, 0.81 for serum 5-HIAA and 0.76 for CgA, respectively. Conclusions: The LC-MS/MS assay for serum 5-HIAA discriminates between healthy individuals and patients with NET and is well suited for the diagnosis and follow-up of NETs. (C) 2013 Elsevier B.V. All rights reserved.