Urinary 5-HIAA measurement using automated on-line solid-phase extraction–high-performance liquid chromatography–tandem mass spectrometry

Quantification of 5-hydroxyindole-3-acetic acid (5-HIAA) in urine is useful for diagnosis and follow-up of patients with carcinoid tumors and for monitoring serotonin (5-hydroxytryptamine) metabolism in various disorders. We describe an automated method (XLC–MS/MS) that incorporates on-line solid-phase extraction (SPE), high-performance liquid chromatography (HPLC) and tandem mass spectrometric (MS/MS) detection to measure urinary 5-HIAA. Automated pre-purification of urine was carried out with HySphere-Resin GP® SPE cartridges containing strong hydrophobic polystyrene resin. The analyte (5-HIAA) and internal standard (isotope-labelled 5-HIAA-d2) were, after elution from the cartridge, separated by reversed-phase HPLC and detected with tandem MS. Total cycle time was 5 min. 5-HIAA and its deuterated internal standard (5-HIAA-d2) were retained on and eluted from the SPE cartridges in high yields (81.5–98.0%). Absolute recovery was 96.5–99.6%. Intra-assay (n = 20) and inter-assay (n = 20) CVs for the measurement of 5-HIAA in urine in three concentration levels ranged from 0.8 to 1.4% and 1.7 to 4.2%, respectively. For urine samples from patients (n = 78) with known or suspected metastatic carcinoid tumors, results obtained by XLC–MS/MS were highly correlated (R2 = 0.99) with the routinely used fluorometric method. This XLC–MS/MS method demonstrated lower imprecision and time per analysis (high-throughput) than manual solvent extraction methods and higher sensitivity and specificity than non-mass spectrometric detection techniques.