Discontinuation of proton pump inhibitors during assessment of chromogranin A levels in patients with neuroendocrine tumours

BACKGROUND: The aim of this prospective study was to examine whether discontinuation of proton pump inhibitors (PPIs) or replacement by H(2)-receptor antagonists (H2RA) resulted in a decrease of chromogranin A (CgA) levels in 196 patients with well-differentiated neuroendocrine tumours (NETs). METHODS: Patients with an unexpectedly high CgA level not connected with NET disease discontinued PPIs, or used H2RA instead; 2 weeks later CgA level was measured again. RESULTS: In all, 19 out of 196 (10%) patients showed unexpected elevated CgA levels, they all used PPI. In 11 out of 19 patients with no evidence of the disease, median CgA decreased from 390 μg l(−1) during PPI treatment to 56 μg l(−1) after discontinuation (P=0.003). In 8 out of 19 patients with stable disease, median CgA decreased from 618 to 318 μg l(–1) (P=0.012). In 12 out of 19 patients who ceased all acid inhibition, CgA levels decreased by 82%, while in the seven patients who replaced PPI by H2RA, CgA decreased by 77% (P=0.967). CONCLUSION: Proton pump inhibitor use causes falsely elevated CgA levels in patients with NET. We recommend to stop, or replace PPI by H2RA, to obtain a reliable CgA value.