S3032 Use of Bile Acid Malabsorption Panel or Single Serum 7αC4 and Single Stool Primary Bile Acid Content in Patients With Treated Neuroendocrine Tumors

Introduction: Patients with neuroendocrine tumor (NET) can experience diarrhea due to bioactive products of NET such as serotonin, bile acid malabsorption (BAM), short gut, or steatorrhea. Previous studies using 48h fecal collections showed the presence of BAM in 48/52 (92%) patients with NET (Dig Dis Sci 2022; 67: 2517-25). More recently validated, the BAM panel (BAMP) uses a combination of single stool primary BA (SSPBA) and serum C4 as an easily accessible test to diagnose BAM (Gastroenterology 2020; 159: 1952-4). Aims: 1) To audit the diagnosis of BAM using BAMP in patients with NET. 2) To compare the levels of serum C4 and SSPBA in patients with NET to those of patients with functional diarrhea (FD) with no alternative clinical diagnosis at the same institution. Methods: BAM was defined based on BAMP criteria: C4 >52.5 ng/mL, SSPBA >10%. We identified 23 patients diagnosed with NET who developed diarrhea and underwent BAMP test. Our comparator group consisted of 232 patients with FD and BAMP measured. Fasting serum C4 was measured by liquid chromatography (LC) method (Clin Biochem 2018; 52: 106-11), and fecal primary BA by LC-mass spectrometry method (Clin Gastroenterol Hepatol 2012; 10: 1009-15.e3). Three SSPBA results were excluded due to patient treatment with bile acid sequestrant. We used Mann-Whitney test to compare the values between patients with NET diagnosed with BAM vs no BAM and to compare NET with FD. Results: Patient characteristics are summarized, including location of primary tumor, history of cholecystectomy, pancreatectomy, median length of ileal resection, and presence of liver metastases. BAM was identified in 14/23 (61%) patients with NET based on combination of C4 and SSPBA; 2 of the remaining 9 patients had high serum C4 alone. Patients with NET had median [IQR] serum C4 level of 95 [37, 149] ng/mL compared to 51 [24, 85] ng/mL in patients with FD (P = 0.002). Moreover, patients with NET had SSPBA level of 85 [17, 98] % compared to patients with FD who had a level of 31 [14, 54] % (P = 0.011). Patients with NET were older than the FD control group (P = < 0.001). Conclusion: BAMP is a feasible tool for diagnosing BAM in patients with NET and diarrhea. Though a head-to-head comparison with 48h fecal BA excretion was not performed, the BAMP identified BAM in 61% of patients with NET, showing feasibility of this convenient test to positively diagnose BAM which can help optimize control of diarrhea.