Endocrine Abstracts

Introduction: Chromogranin-A (CgA) is a 49 kDa protein of the granin/secretogranin family originating from dense-core secretory granules within cells of the diffuse endocrine system. CgA is currently the best available diagnostic biomarker for neuroendocrine tumours (NETs) with recent clinical guidelines advocating the measurement of CgA as part of the baseline biochemical profile in patients presenting with symptoms suspicious of a gastroenteropancreatic NET.

5-Hydroxyindole acetic acid (5-HIAA) is also utilised as a marker for patients with serotonin-secreting NETs. Most laboratories currently measure 24 h 5-HIAA excretion in urine samples. However, urine collections are cumbersome and may often lead to inaccurate assessment of 24 h 5-HIAA excretion. More recently, LC–MS/MS measurement of 5-HIAA in plasma and serum matrices has become available.

Method: The aim of this study was to compare serum CgA measurement to both serum and 24 h urine 5-HIAA measurement. We measured serum CgA, 24 h urine 5-HIAA excretion and serum 5-HIAA in paired samples from 20 patients with known 5-HIAA secreting neuroendocrine tumours. Patients receiving PPI therapy were excluded from the study.

Results: All results were expressed as a percentage of the reference range. Linear regression analysis of CgA and 24 h urine 5-HIAA gave a correlation coefficient of 0.92 with a corresponding Passing-Bablok regression equation of (urine 5HIAA)=1.41×(CgA)−0.31. Linear regression analysis of CgA and serum 5-HIAA gave a correlation coefficient of 0.63 with a corresponding Passing-Bablok regression equation of (plasma 5HIAA)=1.74×(CgA)−0.49.

Conclusion: We have demonstrated a strong correlation between 5-HIAA measurement in both 24 h urine samples and serum samples when compared to the current best available general NET marker CgA. Furthermore, in contrast to CgA measurement by immunoassay, 5HIAA measurement by LC–MS/MS is not susceptible to anti-reagent antibody interference, or the high dose hook effect and therefore offers greater analytical robustness.